View Full Version : 1997 Prostar high engine idle after start

07-16-2008, 05:58 PM
I have spoke with the local mc dealer many times asking about a new download for my ECM without any luck. I thought I would try here to see if anyone else was having the same problem as I was having.

I have a 1997 prostar with ther 350 EFI throttle body set-up 275hp.

Since day one it will idle high after you start the engine and take 5-10 seconds to reach an idle at which it is safe to shift into gear.....very frustrating at times. I have replaced the Idle Control Screw thingy a year or so ago to see if it would help with no luck. I think the ECM program thinks the engine is cold all of the time and tries to "choke" it....who knows.

This happens cold or hot.

Any ideas???

Thanks in advance.

07-16-2008, 06:45 PM
I would find out what the spec is for the idle screw "thingy", which is set by Rochester to the correct throttle plate gap. It's not like a carb- the idle speed isn't set using that, it uses the IAC for that.

Look at the MAP sensor. It has a three-wire harness with a blue, a black and a gray wire. There's a vinyl tube connecting it to the rear of the throttle body. If that's cracked, loose or has any kind of leak, it will need repair. It's possible that the PCV valve is old/bad, or the hose leaks. Does the check engine light ever go on?

Do all of the troubleshooting before you haul off and do a recal. If it didn't run right from day one, assuming you bought it new, it should have been fixed by the dealer under warranty.

07-16-2008, 07:06 PM
It could also be a vacuum leak at the gasket where the TBI bolts to the manifold.

07-16-2008, 10:43 PM
It could be that but I haven't seen it happen from day 1. Still,....

Any vacuum leak will cause this but I would look at the common ones first- MAP sensor, IAC sticking or needing to be re-parked (which a dealer can do by connecting to their diagnostic computer, which I would do anyway since it could cut the diagnostic time, considerably).

If this issue was there from day 1, it should have gone back to the dealer and this is probably something that would be very easy to repair if the right things are looked at. OTOH, being hundreds of miles away makes it a slower process, not that the location is shown in the profile.

07-16-2008, 10:48 PM
I am not sure that his day 1 is when the boat was brand new, that was 11 years ago. I thinking the boat was pre owned but, I could be wrong. He could spray some WD 40 around the base of the TBI while it is running and is this affects the was the engine is running he has found at least one problem.

07-17-2008, 03:57 PM
Day one was when when I bought the boat. It was in 1997. it had 18 hours on it. I have spoke with the mastercraft dealership and they said they all do it, and that it was a problem for that year with that motor. They have had it hooked up and they have downloaded the latest program.

I am not too impressed with any of the dealers around here..

We (meaning our group) have #1 of 25 of the 1993 limited editions, another 1993 limited for sale, 1993 stars and tripes, 1997 sammy open bow, '05 197, 1995 pro tour boat. Mine is actually a 1997, T-bar, tandem trailer, polished undergear mint condition boat. I have aluminum heads on it is running up there with the 310hps' now, or faster. Not the problem......general ideas of mastercraft is also not the problem. We also have a certifed M/C mechanic in our group, but does not have access to the necessary programs to deal with downloads anymore.....since the buyout.

My question really is this.....is the dealership full of crap as usual by telling me "they all do it" or is there, could there be or is it possible that there is a ECM hack of somesort so that I can fix it myself.

I have a Powercommander that we use on the Harleys. It eliminates the onboard ECM and you can adjust fuel/air ratios, idles settings etc. by using a laptop. It is a shame that no one has come up with something for the comp boats etc.

I will check some of the other ideas that you have spoke of to see if I can come up with a resolution. Maybe one of the connections, hoses or wiring had been overlooked since "day 1".

I will keep you posted.

07-17-2008, 04:34 PM
When you post "around here" but don't say where "here" is, it makes doing something about the problem, difficult.

"but does not have access to the necessary programs to deal with downloads anymore.....since the buyout."

What buyout? MC? If he works for a dealer, he should be able to work a deal. If he no longer works for an MC dealer, they're not just going to provide him with resources that are only for dealers, certified or not.

There are ways to go into the ECM and the program is somewhat proprietary but it's still possible. They don't provide this info to customers because of liability issues and because not that many actually know what to change, and by how much. Making changes without seeing the results (using only "seat of the pants as the basis for thumbs up or down) isn't usually the best way to adjust one of these.

What heads do you have and how are they different from the cast iron ones? I would guess that they weren't in it "from day one", right?

I started working on these in '98 but never heard anything about "they all do it". If "they all do it", the dealer probably doesn't have the training, general knowledge or desire to do the job right. Is that dealer still selling boats?

You mentioned that maybe the ECM thinks the motor is cold- did you check the ECT? If you have black deposits around the exhaust flaps and go through gas like crazy, I would guess that the coolant temp sensor (ECT) or the harness may be at fault. I have heard these go into high idle, but it wasn't all of them. Like any other motor, it doesn't want to be run hard when it's cold. If letting it warm up is a problem for you, I need to ask if you let your car, truck or bike warm up. I have a GM TBI in my truck and it goes to high idle, too. It's supposed to if the temperature is cold enough.

The idle speed is controlled via the IAC, by the ECM. If it idles at more than 600 RPM all of the time, I would say it has a vacuum leak or the IAC needs to be reparked but since it sounds like the idle speed drops to normal after that annoying 5-10 seconds, I would check into the ECT and its harness/plug.

"I have a Powercommander that we use on the Harleys. It eliminates the onboard ECM and you can adjust fuel/air ratios, idles settings etc. by using a laptop."

I would think the Power Commander replaces the ECM, not eliminates it.

RE: easy recal for comp ski boats- Do you actually think you have the facilities to do more extensive testing than MC and Indmar? Have you thought about how much it costs to develop something like that, get it to work well, get product liability insurance and then realize that MC makes about 4000 boats a year, with a small percentage of boat owners wanting to do this? Harley makes more bikes in a month than MC, Nautique, Malibu and Supra/Moomba make in a year.

07-17-2008, 08:01 PM
My 97 prostar 205 with the Lt1 does the same thing. Cold or hot it goes to 1500 for about 5 seconds then settles into a normal idle. Runs great besides that.

07-21-2008, 11:50 AM
Yeah...mine runs great, it's just the starting that gets annoying.

I will check out some of the ideas that other have come up with to see if there is a problem that the dealership did not find back in the day/s.

07-21-2008, 12:44 PM
To be honest, if the idle drops to 600 RPM and is very stable, I don't see a problem. If it varies or stays high, there is. Any motor needs to warm up and if it takes 5-10 seconds to drop to 600 RPM, I can't see that as a hardship. Do you let it warm up at all? Do you do a pre-start check before you go out?

07-21-2008, 03:37 PM
I guess I forgot to mention that it does it hot or cold.

It is something I have had to deal with. I ran across this site again while surfing and forgot that I had been a member here from a couple of years back and thought I would give the forums a quick shot to see if there was a quick fix remedy.

Electrical problem shooting is not my specialty....

Anyway, I will be up at the lake this weekend and see what I can come up with.

07-21-2008, 08:46 PM
As I said, I don't know that it actually has a problem. If the motor is hot and it sits, turning the key to ON will show the actual temperature of the coolant and in summer, it can go over 230 degrees which by itself, isn't a problem. Running it at that temperature would be, though. If the ECM tells the IAC that it wants the motor to idle until the temperature drops, it will and there's nothing you, or anyone else, can do about it. When it's a cold start, it will generally go to high idle and then settle down. At least it's not a carburetor with alternating hot and cold starting issues.

07-22-2008, 05:34 PM
As I said, I don't know that it actually has a problem.
My first thought was the same as Jim's. More detail would help though. What does it "rev up to"? And REALLY, how long does it take to settle down? Not what it "seems like".

I'm not doubting you, I just want to understand the engine's behavior better. .

I'm talking hot here.

If the dealer can't help you, and everything is functioning apparently correctly (no vacuum leaks etc), then there ARE ways of "fixing" it. "By the book'ers" won't like it though.

07-22-2008, 06:09 PM
"If the dealer can't help you, and everything is functioning apparently correctly (no vacuum leaks etc), then there ARE ways of "fixing" it. "By the book'ers" won't like it though."

First of all, MC dealers don't generally make small changes to the program, they do recals and check for codes. Besides, it still runs great after 11 years, why bother to make a change when there's not actually a problem. Besides- we don't know exactly what was checked in the past. The dealer could have sent the ECM in to Indmar the first winter, but it doesn't seem like that was offered as an option.

If boat techs had the same kind of training system as auto techs, we wouldn't have much to talk about in the repair and maintenance threads, but while the industry as a whole is very large, the industry-wide tech training lags behind for a couple of reasons:

High turnover rates in the service end, partially due to the fact that very few techs see this as a long-term career. Also, they're not paid that well unless they have an exceptional skill set and attitude.

The systems aren't as advanced as car/truck systems.

It's s seasonal industry and many dealers reduce staff levels in winter, in cold areas, unless they have enough service work for the "slow season".

There aren't as many boat dealers that aren't close to some body of water, so distance to the jobs is sometimes excessive.

How far can a boat tech advance? In most cases, for one reason or another, not very.

07-22-2008, 06:56 PM
Jim, I completely agree with you that we definitley don't have a clear understanding of
1. what all has been done to the motor
2. What all has been checked
3. Or even what the symptoms REALLY are!

I'm not advocating anything at this point...except to get more useful input from the OP so we have a chance of helping the guy. He's got to tell us more and it's got to be more to the point. But to answer the question you posted:
why bother to make a change when there's not actually a problem.
Because he doesn't like it. Same reason people do mods to car; to make them behave the way THEY like. Nothing wrong w/that, IMO, if the end result is a fine runnign machine that makes the owner happier than it did before.

I don't know what "life in the boat bussiness is like" was all about but I totally symathize and agree. I have to deal w/the same things in the ski industry. My crew works on $400,000, drive by wire, snow cats that have 3 different ECM's in them....and they get paid ~$15/hour. Staff retention is a pipe dream, and therefore, "experts" are too.

07-22-2008, 07:34 PM
I still haven't seen a response to me asking what "since the buyout" means. I never saw a response to me asking what heads are in it, either.

Regardless of whether the MC tech in the group can get recal programs, if he was trained to work on these, he should be able to diagnose it. Is it possible that the aluminum heads are causing the MAP sensor to send info to the ECM that the program doesn't like? Maybe.

"Yeah...mine runs great, it's just the starting that gets annoying."

This tells me that it doesn't actually have a performance issue. If it's annoying to lose 5-15 seconds at startup, I see that as someone being very impatient. I don't really like when I ask a question and it isn't answered by the person I'm trying to help, either.

07-22-2008, 07:39 PM
"Because he doesn't like it"

Most people learn to live with the things they can't change. Could Indmar have used the high idle for a specific purpose? Sure. If that high idle cycle is deleted, is it possible for a problem to arise? Sure.

Maybe Engine Nut can add something. I think he'll need to know what heads are on the motor, though. I also think he might want to know what was done, in an effort to troubleshoot this, the same as us asking this question. It would help to know which direction the troubleshooting was going.

07-22-2008, 08:17 PM
I don't really like when I ask a question and it isn't answered by the person I'm trying to help, either.
I agree. The OP is being a little cryptic here. I don't know why.

Most people learn to live with the things they can't change.
Well I can't agree w/that. You CAN change it. Perhaps not in a "conventional" way but you can change stuff all you want. My '06 Corvette is a perfect example; I think that the exhaust sounds like crap. A conventional way to "fix" that is to buy a $1500 exhaust system. I've done that (twice), and found unacceptable results. So, I bought three stock take-off's and I'm cutting/welding fabbing my own design to get the sound I want. Prototype # 1 got me about 1/2 to my acoustical goal. Working on "prototype #2" now. Could GM have designed the stock system for a specific purpose? Sure. Is it possible that my modded system may hurt performance? Sure (but not likely). But to not even try...that's some scared y-cat living if you ask me. If you are not happy w/something why not TRY a change?

Anyway, you're right; this thread needs the OP to step up w/a LOT more info.

07-22-2008, 08:29 PM
Not everyone wants to mess around with their stuff- either they don't know how or don't want to spend the money.

If you want a different sound, great- are you able to determine the flow characteristics? Is you can, even better than just welding it up and using it. If the stock system wasn't what you wanted because it's not loud or deep enough, remember that they also have noise levels to deal with when they make a product.

"But to not even try...that's some scared y-cat living if you ask me. If you are not happy w/something why not TRY a change?"

Take a good cross-section of the general population and I would bet that the vast majority have never modified a thing in their life. I like to mod things, but like I said, it's not for everybody. This boat doesn't have an actual problem, IMO, but without more info, it'll be hard to determine. Aside from changing the IAC settings in the first 15 seconds, I don't know what he'd be able to do.

Re: your exhaust note- just put straight pipes on and be done with it. Or, aren't you from Northern Indiana?

07-22-2008, 08:54 PM
I agree w/your post, and your point about the majority of the population. You're right, that most people can't/don't want to/don't understand.

But at least give them the OPTION, IMO. Tell them the options, and the risks. Let them decide. I know for a fact that I've helped more than one person on this forum using "unconventional methods" when other methods had failed for what ever reason.

I'm not using straight pipes (I actually tried that for S&G's for about a day) because all it is is LOUDER. It doesn't improve the character or quality of the sound...nor did I really think that it would. Likewise, the stock system wasn't "too quite" -though it IS very quite. It also has the same character and quality, which I don't like. I'm not from No Indiana (does everyone there run straight pipes or something?) I'm from Park City, UT.

07-22-2008, 11:05 PM
I never said they shouldn't have the option to change things but why change for the sake of change if it won't improve something? Cosmetics is one thing but engine control is another. I have never seen pinstripes or flames cause a motor to scatter.

I was kidding about the straight pipes, BTW. I HATE the sound of straight pipes but that's what I was referring to when I asked about N Indiana. Every time I went there for MC training, most of the cars and trucks had them. OTOH, one of the guys at Alan's place makes really nice exhaust systems, but they have 4 dynos, mandrils, macjine shop and flow benches, etc.

Any problems with standing waves?

07-23-2008, 12:10 AM
Well, I've never seen an engine scatter b/c of a desire to change engine idle RPM. But I know what you're saying. :)

By standing waves, are you referring to "drone"? Of so, yes. It is a big problem on the C6. My first attempt isn't bad at all compared to most after market systems I've heard though. My "plan" was and still is to try two different concepts for improving the character and quality of the sound. If I am successful at achieving the sound quality and character I like, then my other idea was to weld in a tuned length, 1/4 wave pipe to quell the resonance at the problem RPM (~1800-2000). That's a ways down the road though. First I need to get it to sound like it "should".

I didn't want to get into talking about exhaust too much b/c I didn't want to hijack this guys thread....but he doesn't seem to "into it" so, if you're interested, here is a clip of my car, stock exhaust w/GHL "Cat back" (really, mufflers and tail pipes on a C6). It's pretty representative of what all C6's sound like, character and quality wise; Too much upper base drone/cylinder firing noise and not enough "bubbly" V8 sound.

Here is attempt number one. It IS smoother...
...but still too much "BLAAAA-BLAAAA-BLAAAA-BLAAAA-BLAAAA-" and not enough "La-La-La-La-La-La-La-" if that makes sense.

Here is a car that is my bench mark. Same engine (LS2) same power, same firing order, same cam, same intake, same heads...same-same...yet listen to the sound "roll" out of those pipe right after start up. That's what I want. Note especially the sound BEFORE the burn out.
Anyway, that's my current quest. I'm not an acoustic wizard by any means, so I'm sort of grasping at straws here, w/my concepts and ideas for improvement.

07-23-2008, 12:25 AM
Do you notice a drop in power at that RPM range?

An exhaust pipe is just that- a 1/4 wave resonator. You might be able to get rid of the problem by welding in a section with a slightly larger diameter, somewhere ahead of the mufflers. Ford basically did this on the '55 - '57 T'Birds and they were called 'resonators'. The larger diameter section will slow the air flow down, but will still move the exhaust gas volume.

07-23-2008, 08:44 AM
The high idle happens hot or cold.

The high idle happened prior to installing different heads. (heads were installed a couple of years ago, makes no difference what type of heads because the idle at start problem did not go away).......

My boat does not come with engine coolant??? It uses lake water to cool it, you know Jim....the impeller at the front of the engine that draws water up from the lake, cirulates it through the motor and discharges out the back of the boat along with exhaust fumes.

For lubricant I use Mobil 1 every 25 hours

07-23-2008, 09:45 AM
The high idle happens hot or cold....The high idle happened prior to installing different heads.... It uses lake water to cool it...I use Mobil 1 every 25 hours...boat idles high at start, hot or cold. It does eventually drop down to normal idle.
Well, you still didn't answer any of my questions either.

So back to exhaust. No noticeable power loss at the "drone" RPM. Not SOTP anyway, but we all know about the SOTP meter. :)

My first attempt was basically what you suggested; a large resonator. My idea was to have a BIG common chamber that would give the exhaust pulses time/space to blend/mellow. What I did was cut out the whole mid section of the factory H-pipe, about 3' long. Then I welded a top plate, bottom plate, and a front and rear cap on. Ultimately, it looks like a 3' long 6" wide, 2.5" tall, 2 in/2 out muffler, but it's hollow inside. "Take II" is going to be the complete removal of the "H" crossover pipe, since the GTO which sounds so nice, does w/o that and has completely independent, dual exhaust. Another idea I had was to weld in a Dynomax "X-Flow" muffler in the place of the factory x-over pipe. All ideas I'm pursuing as time allows. I know that what ever I do, it does have to be ahead of the mufflers, b/c changing the mufflers doesn't change the characteristics that I'm trying to change at all. I wish I had a better understanding of acoustics as it relates to engines. I've done several custom exhaust mods before that were for acoustical goals only, and they were very successful. But w/this system, I'm having a much harder time.

07-23-2008, 02:23 PM
There's no need to stay out- that was basically a side discussion, not meant to drive you away.

"Not a world wide buyout, not a stock exchange and not that crap-*** idea that MC had in 1998 when they released nothing but crap.....you know JimN....when they released a prostar that would not turn, a prostar that had to have fins put on the rudder to make them turn, a prostar that had to have fiberglass glued into the outer rear corners of the hull to make them turn.....how do I know, because some of my group were there, at the factory trying to get that pos year model to work right. They decided to go on the cheap, it failed."

The hydro-rails helped with a problem, but neither of us were there for the design/budget process, so I think saying that they went cheap is unfounded. That hull wasn't a good one and they replaced it soon after, which was very costly to them, in several ways. That was definitely a bad period for them and because you use their boats, for you, as a skier. However, you're complaining about the hull, not the motors, in general, and while they changed to Vortec heads and a new ECM, I don't think the motors fell under the "crap***" designation.

"The high idle happened prior to installing different heads. (heads were installed a couple of years ago, makes no difference what type of heads because the idle at start problem did not go away)."

Since it's almost impossible to answer a question about an 11 year old boat without knowing more about its history, was changing the heads purely for increasing power or was it also an attempt to cure the high idle issue?

"My boat does not come with engine coolant??? "

The fresh water, brought in by the raw water pump is your coolant. Regardless of whether water or anti-freeze/coolant is used, the fluid in the engine that maintains proper operating temperature is the coolant unless it's specifically air-cooled, which these aren't. The coolant temperature sensor (ECT) reports the temperature to the ECM, which may have a programmed interval, based on the ECT indication. If your sensor is reading low, it may cause the ECM to go into high idle, even though the coolant isn't cold. That's why I asked what the tech looked for when they tried to diagnose the problem.

"For lubricant I use Mobil 1 every 25 hours, why....because I can and I want to."

I don't remember addressing this, but it's great oil, so if you want, keep using it- I won't try to stop you for any reason.

"We can go over this many times, but the dealership had told me there is nothing they can do and that it was something the 1997 model do."

And, having been at MC training in March of '98, I did see some motors that idled high after running and even in later training, it wasn't mentioned as a recurring issue but in truth, just about any odd operation can be diagnosed if the tech knows to look in the right place. Sometimes, the IAC will stay more open than its "home position" and if this occurs, I could see it causing a high idle. Once the startup sequence is over, it can be closed to the point that normal speed is achieved. The IAC can be "reparked" by using a diagnostic computer and is one of the manual functions.

"Is it right NO! There are many other 1997's around me in the water and most do not have this problem, it was not something that MC brainfully decided to stick into my boat to test my patience."

Since others don't have this problem, there must be a cause. I have offered my opinion on what it may be- sticky IAC not allowing full closure at "repark", coolant temp sensor/harness issues causing the ECM to think the engine is cold, or the ECM program may have a fault. Without having the boat, there's not much more I can do. If the ECT and harness, IAC and program weren't checked, we can't know if one, or more, of these is the cause.

I don't care how many posts I have and some here have over 10000 more, even though they registered at the same time. Post count isn't important to me, at all. I first posted because someone was annoyed by their warning buzzer and someone told him to disconnect it. I explained why that's a bad idea, especially on a boat that's under warranty. I don't engage in as much socializing as many others here. As a former MC tech, I came to offer some tech help and to keep up on my diagnostic chops. Others here have much more experience with these than I do and when I don't know an answer, I defer to them but without information, even someone who works for Indmar or did the original testing for the calibrations can't determine the cause of a problem like this.

Stay as long as you like. I don't see any reason to leave and who knows- we might even get rid of this problem.

07-23-2008, 02:26 PM
I don't remember seeing what part of the country you're in. Did you order your boat, or did your dealer get it from another dealer?