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BG1772
05-16-2005, 11:01 AM
Hello,

I have an '01 X-Star with the 5.7 LTR motor. The engine sporadically idles between 600 and 1200 RPM and will eventually even out and idle at about 1000 RPM. It does not matter if the engine is hot or cold. Iíve changed out the Idle Air Control Valve and it did not make a difference. However, when I borrowed the IAC off of my friendís X-Star, the idle seemed much better and was maintained about 680 RPM. Does anybody have any suggestions?

east tx skier
05-16-2005, 11:59 AM
Does it hang at all when you are cruising and bring it back to idle?

BG1772
05-16-2005, 12:17 PM
When I bring it down from higher speed it will tend to go back down to around 1200 RPM then bounce around between 800 and 1200 and will finally settle on about 1000. This takes maybe 10 to 15 seconds.

east tx skier
05-16-2005, 12:33 PM
My 93 would hang at 1,200 because the throttle cable was at an angle and would bind at the joint. If I killed the engine, the perfect pass servo would wind up and bring it back to normal idle. Sounds like a different issue in your case, but you might check to see if your throttle cable is doing its job pulling everything back to neutral.

Tom023
05-16-2005, 12:39 PM
EFI has a lot of benefits, but being user friendly to work on isn't one of them. When I got the LTR I pretty much figured that intake engine issues would require the skills of a certified mechanic. Sorry I can't help on this one.

OhioProstar
05-16-2005, 01:45 PM
Doug I had the same problem with mine. The throttle cable would not allow the throttle arm to drop back to slow idle. I would have to re-start the engine and the computer would keep the idle low and once I would run the RPMs up and then try to idle again it would hold above 1000. I replaced the IAC before I caught the simple re-routing fix.

east tx skier
05-16-2005, 02:07 PM
For me, it was a $30 mounting bracket to raise the rear portion of the throttle cable up. It was all a result of the new intake manifold. I still say the results were worth the headaches. Boat runs better than ever. Screams out of the hole all the way up to ski speeds.

BG1772
05-16-2005, 03:09 PM
Thanks for the info guys. I'll take a look a the throttle cable. I hope it is that simple, but I'm thinking it will not be. In my situation it starts as soon as I turn the engine on - even before moving the throttle.

east tx skier
05-16-2005, 03:34 PM
Look for some slop in your cable. I had that problem before the hanging problem. I'd start it up and it'd rev up to about 2,500 rpm before I could kill it. May not be as drastic in your case, but just happened to be in mine.

Engine Nut
05-16-2005, 05:34 PM
Idle RPM of 1000 is too high. Possible problems. Bad IAC. Did your replacement come from an auto parts store or from a marine dealer? It might not have the correct specs since the one from your friends boat seemed to cure the problem. Did your IAC in his boat work OK? Other possibilities, TPS out of range, intake air leak. Do you have access to a scan tool or Diacom software? That might be the best way to get to the bottom of the problem.

Engine Nut

OhioProstar
05-16-2005, 05:38 PM
Good thought Engine Nut, if his IAC works in his buddy's boat then that eliminates it as a possibility.

OhioProstar
05-16-2005, 05:44 PM
As an FYI the IAC for a 1995 350TBI is AC-Delco #217-429 and GM part #17113099. I found this out the hard way when I bought the $170 MC Part # S556094 and it came with a MC sticker covering the GM sticker. The GM part is like $50.

BG1772
05-17-2005, 08:35 AM
The next thing we were going to try is to put my IAC in his boat - we ran out of time the other day. I bought the IAC through NAPA, but I do not recall the part number. I have a friend who is a mechanic and has a scanner and we are going to give that a try. Thanks for the part numbers on the IAC, it took me 2 days to track the part down. I had called MasterCraft to order, but got sticker shock on the price - I could not justify $188 for a part that I knew should only be about $50. How do you check the TPS to see if it is out of range? I've looked for air leaks by spraying the throttle body and plenum with carburetor cleaner and listening for changes in engine performance. Do you have any other recommendations for finding air leaks?

OhioProstar
05-17-2005, 09:03 AM
Aside from spraying a little WD40, I would think the next step is hooking it up for codes that have been tripped. Good Luck

Engine Nut
05-17-2005, 12:17 PM
The next thing we were going to try is to put my IAC in his boat - we ran out of time the other day. I bought the IAC through NAPA, but I do not recall the part number. I have a friend who is a mechanic and has a scanner and we are going to give that a try. Thanks for the part numbers on the IAC, it took me 2 days to track the part down. I had called MasterCraft to order, but got sticker shock on the price - I could not justify $188 for a part that I knew should only be about $50. How do you check the TPS to see if it is out of range? I've looked for air leaks by spraying the throttle body and plenum with carburetor cleaner and listening for changes in engine performance. Do you have any other recommendations for finding air leaks?

Checking the TPS voltage is a scan tool job. Normal TPS voltage with key-on and throttle closed is .7 to .8 volts. As you open the throttle, the voltage increases to close to 5 volts. I have attached a chart showing the typical scan tool values fron an EFI engine.

Engine Nut

BG1772
05-17-2005, 01:08 PM
Thanks for the info on checking the TPS. I'll give that a try. Hopefully this is the problem.

JimN
05-25-2005, 08:51 PM
Engine Nut- what about back probing the TPS? Or do you not want to recommend that to eliminate the possibility of damaging the silicone seal and having moisture getting in?

Engine Nut
05-26-2005, 07:56 AM
Engine Nut- what about back probing the TPS? Or do you not want to recommend that to eliminate the possibility of damaging the silicone seal and having moisture getting in?

Back probing the TPS is just fine. Quilters "T" pins from the sewing department at Wal-Mart work just fine. Attached is a diagram showing how the TPS is wired in the system.

Engine Nut

BG1772
05-26-2005, 04:07 PM
I thought this had dropped off the fourm. Anyhow, last weekend I was able to put my friend's computer on it and the computer pointed to the TPS. Got a new one at NAPA and everthing is working great now! Thanks for the help.

JimN
05-26-2005, 06:20 PM
Engine Nut- should we talk about getting the codes from the MIL on the dash?