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View Full Version : '96 prostar 205 Fast Idle


stuttgart
05-04-2007, 04:45 PM
My 1996 prostar 205 with the Indmar and TBI has been acting up lately. Sometimes I start it up and it idles like normal, but other times it will jump up to 2000rpm and just stay there. It will also do this after running at speed for a while, when i pull the throttle back it will just sit there idling at 2k. I took off the filter and the butterflies, cables are fine, no issues with sticking. It also stalls upon rapid throttle advancement.

Wondering what else it might be, any ideas? THANKS.

Ryan
05-04-2007, 05:05 PM
My 1996 prostar 205 with the Indmar and TBI has been acting up lately. Sometimes I start it up and it idles like normal, but other times it will jump up to 2000rpm and just stay there. It will also do this after running at speed for a while, when i pull the throttle back it will just sit there idling at 2k. I took off the filter and the butterflies, cables are fine, no issues with sticking.

Wondering what else it might be, any ideas? THANKS.

Any chance the bracket holding the throttle cable near your TBI is loose? If it allows for slight movement, then holds it in place, and back again etc... it could be the cause.

Ryan
05-04-2007, 05:14 PM
Unless of course it's jumping to other RPMs at starting w/o touching the throttle.

JimN
05-04-2007, 05:14 PM
Check the throttle cable to make sure it's free to move easily and look at the PCV valve hose for breaks, holes, etc. Check the PCV valve, while you're at it.

The IAC may be sticking, too.

Diesel
05-04-2007, 05:34 PM
Check the throttle cable to make sure it's free to move easily and look at the PCV valve hose for breaks, holes, etc. Check the PCV valve, while you're at it.

The IAC may be sticking, too.

Yep, clean the IAC interface at the throttle body. Do you have CEL?

stuttgart
05-22-2007, 10:25 PM
Thanks for the help guys.
No check engine light.

I cleaned the IAC (it was a little dirty), checked throttle position sensor, cable, etc. but still has a fast idle, and now it's stalling when I quickly advance the throttle. Smells awfully rich and smoking a little too much which makes me think the timing is off. I'll have to check it this weekend. Any other ideas...?
Thanks

JimN
05-22-2007, 11:12 PM
What happened just before all of this started? Any particular event or service done on the motor?

Remove the flame arrestor, start the motor and watch the IAC pintel when you increase throttle position. It should open more and close as the throttle closes. Also, watch the fuel spray pattern- is it a regular, symmetric cone or are there gaps? I don't think I need to tell you not to go too close to an open throttle body while it's running.

If you don't know for a fact that the timing is correct, go ahead and check it, but it needs to be in diagnostic mode to set base timing. Make sure the coolant temperature sensor is plugged in, too. The one you want to check is the two wire sensor, usually located in one of the heads- it'll have a yellow wire and a black wire.

stuttgart
05-24-2007, 10:25 PM
No big events recently, the fast idle came up last year before I winterized but I freed up the throttle cable and thought i'd solved the problem.

I took another crack at it today...

-There is no noticeable movement of the IAC pintel with throttle movement, but you really can't get a good look at it.

-The injector spray pattern isn't perfect, but it's pretty consistent.

-At 1000rpm timing was at 14-16 degrees BTDC, but... when I jump the the A and B connectors to put it in diagnostic mode the timing comes down to 10 degrees BTDC, weird...

-Also, when I i was using the timing light i noticed that i was not getting consistent spark, so that lead me to check the distributor cap. It was corroded to ****, so i THINK i've found the culprit.

Does anyone know the part number for a generic Delco EST cap and rotor? and is there any trick to pulling the rotor off? I pulled pretty damn hard to no avail, I don't want to break it.

Also does anyone have a generic ignition coil part number?

Thanks for all the tips everyone!

JimN
05-24-2007, 11:03 PM
The timing is supposed to drop to a consistent setting at 1000 RPM- that's how you put it into diagnostic mode and adjust/set the base timing. You found out that yours is set to 10 BTDC, which is where it's supposed to be. If you look at base timing, it should be rock steady at whatever it's showing but out of diagnostic mode, it jumps around, which is totally normal. It's called 'Spark Stabilization' and is there because people like their motors to run very smoothly, regardless of whether it's normal to have a bit of roughness or not. Don't worry about it, it's there by design.

You won't get fast idle because of a dirty cap/rotor but it can be kind of rough. Old plugs and wires will do the same thing.

If your coil was bad, you'd know it. Change the wires, including the coil wire but clean the tower and coil wire terminal before you do anything else- that can be the whole problem. If you're replacing the cap and rotor anyway, breaking the old rotor is hardly the end of the world but they are usually hard to remove. If it just won't come off, use a hacksaw to but part way through the plastic and use a flat blade screwdriver to split it and either blow the dirt out or vacuum it out. The end of the shaft will probably be rusty, so use a piece of Scotch Brite to clean it and grease it before installing the new rotor. If you call for a new cap and rotor, tell them it's for a late '80s to mid '90s Chevy pickup with the IC module in the distributor. I have been using the Borg-Warner parts for a long time and have been very satisfied with them. Use the Gold series parts, with the brass inserts on the cap. Checker, Schuck's and Kragen sell them and I think NAPA, too. They used to come with a 5 year warranty, too.

Check the IAC by turning the key off and with a bright light, look into the hole- the pintel should close completely and then open a bit. If it doesn't move at all, get a digital multi-meter and measure for voltage across the green pair and then the blue pair. If you see no voltages, there may be a problem with the ECM or the harness. You'll then need to check for continuity from the ECM pins to the IAC plug and the wire colors are the same at each end.

There are two large plugs attached to the ECM and they're called J1
and J2. The wires to the IAC are positioned and numbered as:

IAC Plug position A 441 Blu/Wht J2-28 IAC coil "A" High
IAC Plug position B 442 Blu/Blk J2-13 IAC coil "A" Low
IAC Plug position C 443 Grn/Wht J2-14 IAC coil "B" High
IAC Plug position D 444 Grn/Blk J2-19 IAC coil "B" Low

stuttgart
05-25-2007, 12:18 AM
Thanks for all the info Jim. I really appreciate it. I hadn't seen that test for the IAC, I'll check that tomorrow.

As for the coil, I performed the tests as laid out in the shop manual and there was no continuity between "D" and coil wire terminal "E", which indicates a bad coil.

Also... I noticed that after I shutdown the engine the tachometer just sits at wherever the rpm's were at the time, it never returns to zero.

JimN
05-25-2007, 01:23 AM
If you had no continuity on the primary, it wouldn't run at all. Same with the secondary. The tach staying put is not necessarily an indication of a problem. Bouncing tach or always way too high is usually caused by a bad distributor ground. Maybe you want to check into that while you're looking around.

Are you using only the tach in the dash to read the RPM or are you using another way?

If your RPM is close to 1000 or 1500, have you made sure there are no vacuum leaks? The PCV hose is a good source of extra RPM.

Evan Jones
05-25-2007, 07:50 AM
Once again this forum boggles my mind with all the knowledge and information available to us all. This forum alone would be reason enough to convince me to buy a Mastercraft, regardless of the fact that it is the best skiboat in the world. Kudos to all who put so much time into helping us.

454Barefoot
05-25-2007, 08:06 AM
I had have the same thing going on with my '98 Prostar 310 hp TBI, it will have a fast idle (around 1800 RPM) and all I have to do is turn the key off and start it again and usually it corrects itself, which makes me think its something in the ECM.

JimN
05-25-2007, 09:06 AM
Look at your IAC, too. It "parks" itself when the key is turned off. It can also be reset by connecting to a diagnostic computer and going to that command.

I would do all of the testing possible before pulling the trigger on a new ECM since it won't be programmed when it arrives, and that's not part of teh price unless you negotiate it with a dealer.

454Barefoot
05-25-2007, 09:24 AM
I dont mean to sound like an idiot but what exactly is an IAC

JimN
05-25-2007, 09:27 AM
IAC (Idle Air Control) controls the idle speed. The ECM controls it but it's the actual mechanism for this. It won't set a code and isn't a sensor.

stuttgart
05-25-2007, 07:53 PM
I checked the IAC and it does appear to be working properly. Installed new wires, cap and rotor.

I took it by the mastercraft dealer to check for codes and sure enough there was a code for the TPS sensor. We cleared the code and I later installed the new sensor, but... I didn't rotate the sensor correctly when I installed it, which made it run the same as before. I think if I get this sensor installed correctly and the computer reset it will work.

Is there any way to clear the code without a scanner tool???

JimN
05-25-2007, 08:36 PM
It should go away on its own but if it doesn't, check back here and we'll get you going. It should be OK once the TPS is set correctly but see if you can adjust it at the dealership and watch the actual throttle position indicated on the diagnostic computer. Also, make sure it's not the TPS for an LT-1 motor, because they move in the opposite rotation. At WOT, the LT-1 TPS would read 0%. You would know if it was the wrong one because if the TPS indicated 100%, you wouldn't be able to start the motor without opening the throttle.

stuttgart
05-25-2007, 09:44 PM
Well i guess I'm boatless this weekend.

I let it run for a while, but it hasn't fixed itself. When idling its pretty rough and the IAC pintel is wide open, you can hear it sucking in air. If you even touch the throttle it hesitates and stalls or backfires. I even tried clearing the memory by turning the ignition on/off 300 times, no change.

The new TPS is the same as the old one.

Thanks for the help Jim.

JimN
05-25-2007, 10:11 PM
If the idle is rough, check for spark on all cylinders with a timing light and a spark tester if you have one. Also, if all of the plug wires were removed at the same time, re-check the firing order. It happens to EVERYONE. This motor should idle really smoothly.