88 idle problem
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88 idle problem
I just get my first Vette. It is an 88 with 82K miles that has been sitting since 1999. After replacing the fuel sender/pump assembly, fuel filter and cleaning the tank and lines it fired right up.It runs really well with one exception. When the engine warms up and it kicks off high idle the engine surges when it is at idle speed. It seems to run great other than that. Any ideas??
Joined: Dec 2007
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RE: 88 idle problem
Welcome aboard, you most likely have a intake vacuum leak.Check to make sure all vacuum lines are plugged in tight and don't have any cracked lines. Second possiblity could be throttle position sensor. Best to get a Haynes or Chilton manual off Amazon. com. To walk through all the possibilites. GOOD LUCK.
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RE: 88 idle problem
Thanks. I did get a Hayes manual. The "Service Engine Soon" light is on now. I guess I will go find out what the code is and see if that gives me a clue. Iwill check the vacum lines as well.
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RE: 88 idle problem
OK. I've tried a few things to no avail.
[ul][*]I cleaned the throttle plates and body.[*]I checked for vacuum leaks visually and with carb cleaner.[*]The scanner says the TPS is working.[*]I took it to get the codes checked and am getting all kinds of codes. The first time I got 41,43 & 52 which seem to point toward ECM/Prom issues. I verified the the correct ECM and PROM are in the car. I cleared the codes and today got 34,36 & 44 which are MAF and mixture issues. I suspect they are a result of the idle surges. Today after unplugging the computer and reconnecting the diagnosis was clear with no codes.Then, after the light came on, the scanner is no longer able to communicate with the computer. We tried this a couple of time with the same result. What is going on? Bad ECM or PROM? The engine runs smoothly for a short time after resetting the codes until the check engine light comes on and then it begins to surge again. Gas mileage is poor and the exhaust smells rich.[/ul]
[ul][*]I cleaned the throttle plates and body.[*]I checked for vacuum leaks visually and with carb cleaner.[*]The scanner says the TPS is working.[*]I took it to get the codes checked and am getting all kinds of codes. The first time I got 41,43 & 52 which seem to point toward ECM/Prom issues. I verified the the correct ECM and PROM are in the car. I cleared the codes and today got 34,36 & 44 which are MAF and mixture issues. I suspect they are a result of the idle surges. Today after unplugging the computer and reconnecting the diagnosis was clear with no codes.Then, after the light came on, the scanner is no longer able to communicate with the computer. We tried this a couple of time with the same result. What is going on? Bad ECM or PROM? The engine runs smoothly for a short time after resetting the codes until the check engine light comes on and then it begins to surge again. Gas mileage is poor and the exhaust smells rich.[/ul]
Senior Member
Joined: May 2007
Posts: 1,567
From: eastern NC
RE: 88 idle problem
ORIGINAL: avgjoe
OK. I've tried a few things to no avail.
[ul][*]I cleaned the throttle plates and body. [*]I checked for vacuum leaks visually and with carb cleaner. [*]The scanner says the TPS is working. [*]I took it to get the codes checked and am getting all kinds of codes. The first time I got 41,43 & 52 which seem to point toward ECM/Prom issues. I verified the the correct ECM and PROM are in the car. I cleared the codes and today got 34,36 & 44 which are MAF and mixture issues. I suspect they are a result of the idle surges. Today after unplugging the computer and reconnecting the diagnosis was clear with no codes. Then, after the light came on, the scanner is no longer able to communicate with the computer. We tried this a couple of time with the same result. What is going on? Bad ECM or PROM? The engine runs smoothly for a short time after resetting the codes until the check engine light comes on and then it begins to surge again. Gas mileage is poor and the exhaust smells rich.[/ul]
OK. I've tried a few things to no avail.
[ul][*]I cleaned the throttle plates and body. [*]I checked for vacuum leaks visually and with carb cleaner. [*]The scanner says the TPS is working. [*]I took it to get the codes checked and am getting all kinds of codes. The first time I got 41,43 & 52 which seem to point toward ECM/Prom issues. I verified the the correct ECM and PROM are in the car. I cleared the codes and today got 34,36 & 44 which are MAF and mixture issues. I suspect they are a result of the idle surges. Today after unplugging the computer and reconnecting the diagnosis was clear with no codes. Then, after the light came on, the scanner is no longer able to communicate with the computer. We tried this a couple of time with the same result. What is going on? Bad ECM or PROM? The engine runs smoothly for a short time after resetting the codes until the check engine light comes on and then it begins to surge again. Gas mileage is poor and the exhaust smells rich.[/ul]
Check for vacuum leaks real good. Try my way:
Loping idle is vacuum leak. 30 year old lawnmower, or a new car on the lot. If it sucks air where it ain't supposed to, it lopes.
Brick on pedal, block TB arm, anything to get a STEADY idle. 1200rpms or so... Feed starting fluid spray, A LITTLE AT A TIME, EVERYWHERE. Rev increase is the leak.
Did you find it in a tight spot? Light a book of matches, blow it out while the heads are burnin', and feed the smoke to the leak.
Brick on pedal, block TB arm, anything to get a STEADY idle. 1200rpms or so... Feed starting fluid spray, A LITTLE AT A TIME, EVERYWHERE. Rev increase is the leak.
Did you find it in a tight spot? Light a book of matches, blow it out while the heads are burnin', and feed the smoke to the leak.
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RE: 88 idle problem
Amen on the Haynes manual. Not helpful. I'm with you on the vacuum leak. I will try your method this weekend. What about the codes?Is this a seperate issue or a result of the surging idle?
Also, keep in mind this car sat for 9 years before I got it. Does that give any clues? I have read that the injector seals can go bad and leak air. If that is the case will the starting fluid make the idle increase when sprayed around them?
I also read the extensive thread about a similar issue that resulted from a loose ground. I am going to check that. I like to try the easy stuff before getting to carried away. Thanks for any advice you can give!!!
Also, keep in mind this car sat for 9 years before I got it. Does that give any clues? I have read that the injector seals can go bad and leak air. If that is the case will the starting fluid make the idle increase when sprayed around them?
I also read the extensive thread about a similar issue that resulted from a loose ground. I am going to check that. I like to try the easy stuff before getting to carried away. Thanks for any advice you can give!!!
Senior Member
Joined: May 2007
Posts: 1,567
From: eastern NC
RE: 88 idle problem
ORIGINAL: avgjoe What about the codes? Is this a seperate issue or a result of the surging idle?
Also, keep in mind this car sat for 9 years before I got it. Does that give any clues? I have read that the injector seals can go bad and leak air. If that is the case will the starting fluid make the idle increase when sprayed around them?
Also, keep in mind this car sat for 9 years before I got it. Does that give any clues? I have read that the injector seals can go bad and leak air. If that is the case will the starting fluid make the idle increase when sprayed around them?
To recover ECM codes from the 1984 through 1993 Corvette, place a short [paper clip will work] as shown below between pins "A" and "B" on the ALDL (Assembly Line Diagnostic Link) connector. This connector is located under the dash just to the right of the steering column and has space for 12 pins although not all of the cavities will be populated.
32 EGR code, if you have it, is highly likely a vacuum leak, or fouled EGR valve, which is also a vacuum leak.
Yes, injector ports can suck air, and cause loping, cause it's a vacuum leak. You will test that when you do the leak test above. It has to be done almost exactly as described, to find the leak.
.
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RE: 88 idle problem
OK. I got it! It was th O2 Sensor. I did some research on how the system works and the O2 code is the oneI consistantly got. After erasing the codes the car would run smoothly until the service engine light came on and then the idle would start surging. It would only take a short time to set the code which is how long I guess it took for the exhaust gas temp to get up to 600 which is when the O2 sensorwould send a signal. Anyway I decided that since the O2 sensorwas only $21.99 I would try it. When I reached up and grabbed the old one to remove it, the sensor fell out in my hand. It was broken off at the base which explainedthe "exhaust manifold leak" I had been hearing. I put the new one in, reset the computerand $22 later I am in business! Thanks for all your help! Now I can take the top out and enjoy the beautiful fall weather tomorrow.
BTW, I paid $30 for a code scanner that does what I could have done with a paper clip the way it looks
Thanks cwb. I will pass that along.
BTW, I paid $30 for a code scanner that does what I could have done with a paper clip the way it looks
Thanks cwb. I will pass that along.