C4 Idle
Thread Starter
Instructor
Joined: May 2002
Posts: 133
Likes: 1
From: houston tx
C4 Idle
Looking for someone that can help me with an idle problem with my 88 vette.my idle stays between 1100-1200 rpm i have tried everything,sometimes it does goes down to 650-700 rpm but very rarely and when i turn the engine off and restart it goes back for this reason i dont think it is a vacuem problem even though i have checked for leaks.when i go thru the adjust idle procedure in this website when i ground a&b terminals and then disconnect the iac instead of the idle coming down it will either stay the same or go up to about 1400-1500rpm i have listed is what i have done.
replaced iac
cleaned tb
removed injectors and had them sent to Rich for cleaning
new upper intake,tb, and runner gaskets
replaced temperture sensor
checked for vacume leaks
switched out maf sensor with known good unit
anyones help would be greatly appreciated becouse i am very frustraded.
[Modified by mak567, 4:32 AM 1/22/2003]
replaced iac
cleaned tb
removed injectors and had them sent to Rich for cleaning
new upper intake,tb, and runner gaskets
replaced temperture sensor
checked for vacume leaks
switched out maf sensor with known good unit
anyones help would be greatly appreciated becouse i am very frustraded.
[Modified by mak567, 4:32 AM 1/22/2003]
Burning Brakes
Joined: Nov 2000
Posts: 1,040
Likes: 2
From: BowlingGreen KY
Re: C4 Idle (mak567)
Ground A&B.Unhook the timing connector by the computer under the hood. Turn the ignition on but do not start the car. Wait at least 30 seconds then unhook the IAC connector. Remove the ground from A&B and start the car. Keep it running in park and adjust idle screw until you have about 450-500 rpms. Then turn the car off, plug the Iac and timing connectors back in and start the car. This should work. Also, you should check your tachometer, alot of times they are very inaccurate and cause people to think the car is idleing high when in fact it is not. My factory tach reads about 1200 rpms at idle and the aftermarket tach in my car reads 650 rpms. I thought I had an idle problem for years until I put in a new tach. :cheers:
Thread Starter
Instructor
Joined: May 2002
Posts: 133
Likes: 1
From: houston tx
Re: C4 Idle (KYVette90)
well i tried what you told me that did not work.i am using a snap-on scanner so i know that it is not the tac,also you can hear the the car idling very high.mybe you can explain something to me . i removed the iac from the tb when igrounded a&b terminals and turned the ignition on should'nt the iac move,well it did not.if that is the case would i have a bad ecm or chip .the chip is an ads which i got with the car so i do not have the stock one.that is the only non-stock item on the car. :confused:
Racer
Joined: Jun 2002
Posts: 278
Likes: 0
From: Perry Ga
Re: C4 Idle (mak567)
I had the same problem with my 88, replaced the iac was the first thing, didn't solve the problem, so I took the throttle body off and cleaned it, then replace the tps sensor. (tps seemed to be sticking, I could feel it in the gas pedal.) I thought it solved my problem, Idled at 6rpms for some time until a few weeks ago starts that 8 to 9 rpm idle at times. I think that the throttle body is bad. Thinking of getting another. I think I will clean one more time and spray some silocone in the joints of the throttle body first to see if it will free up the stickage.
Racer
Joined: Oct 2000
Posts: 460
Likes: 0
From: Lincoln NE
Re: C4 Idle (mak567)
If you have an automatic transmission, this is something to look at.
This is going to sound way off base, but it is something to check. I am having an idle problem with mine also (will not idle at a steady rate, especially in Park and Neutral), so I've looked through several of the books I have (Corvette Fuel Injection, How to Tune and Modify Chevy Fuel Injection, the Chevy Service Manual).
In one of the books the first thing they say to check with an idling problem is the Park/Neutral switch. Now you will probably be muttering "WTF is this idiot thinking...", but it made sense when I thought about it. The switch tells the computer what position the transmission is supposed to be in and adjusts things accordingly. The switch can be out of adjustment, worn out, or there could be a wiring problem. Like I said before, it's something to check and eliminate.
Good luck! I know how you feel, my problem is driving me crazy.
This is going to sound way off base, but it is something to check. I am having an idle problem with mine also (will not idle at a steady rate, especially in Park and Neutral), so I've looked through several of the books I have (Corvette Fuel Injection, How to Tune and Modify Chevy Fuel Injection, the Chevy Service Manual).
In one of the books the first thing they say to check with an idling problem is the Park/Neutral switch. Now you will probably be muttering "WTF is this idiot thinking...", but it made sense when I thought about it. The switch tells the computer what position the transmission is supposed to be in and adjusts things accordingly. The switch can be out of adjustment, worn out, or there could be a wiring problem. Like I said before, it's something to check and eliminate.
Good luck! I know how you feel, my problem is driving me crazy.
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Melting Slicks
Joined: Jun 2002
Posts: 2,168
Likes: 16
From: Phoenix AZ
Re: C4 Idle (mak567)
As far as the throttle body sticking, you may have adjusted your minimum idle air adjustment screw TOO FAR out in an effort to bring the idle down. Thats what happened to me and it has been explained to me by more than one TPI shop that if you do this the throttle body WILL bind and stick.
Drifting
Joined: Aug 2002
Posts: 1,773
Likes: 123
From: Birmingham AL
Burning Brakes
Joined: May 2002
Posts: 986
Likes: 99
From: Collegeville PA
Re: C4 Idle (crheinish)
It still sounds like a vaccume leak to me. Don't forget that the butterflies being open is also considered a vaccume leak. If you set the idle screw too far it actually opens the butterflies. Take the accordian off and look at the butterflies to make sure they aren't being held open by the idle screw. I'm also assuming all plennum bolts, IAC, TB bolts, etc...are tight and gaskets were replaced.
Well...Good luck and let us know when you find it.
***I recently had the same symtoms when I replaced my plennum. Turns out I had 2 vac leaks...plennum bolts not "Completely" tight, and butterflies slightly open!!! :rolleyes:
Well...Good luck and let us know when you find it.
***I recently had the same symtoms when I replaced my plennum. Turns out I had 2 vac leaks...plennum bolts not "Completely" tight, and butterflies slightly open!!! :rolleyes:
Pro
Joined: Sep 2001
Posts: 542
Likes: 1
From: Stuck in the 80's
Re: C4 Idle (Triple Black 88)
FWIW, one of several problems I had due to a bad ECM was high idle. Mine would also move up and down from 700 to 1200 like it was possessed, cold or hot, start up or at the stop light. :eek:
Thread Starter
Instructor
Joined: May 2002
Posts: 133
Likes: 1
From: houston tx
Re: C4 Idle (gbody5)
that is exactly the problem i am having GBODY5 that is whay i dont believe it is a vacume leak becouse it will idle normally sometimes.i also have the idle screw backed out all the way and the idle might come down 100rpm.like i said this is the second tb with the same result. so did the ecm fix the idle problem.GBODY5 we share the same taste in cars i also have a GN and Monte Carlo SS
[Modified by mak567, 2:05 AM 1/23/2003]
[Modified by mak567, 2:05 AM 1/23/2003]
Pro
Joined: Sep 2001
Posts: 542
Likes: 1
From: Stuck in the 80's
Re: C4 Idle (mak567)
Yes, it fixed the idle problem. Also fixed the MAF low voltage/high vacuum error code, low coolant light, and intermittent failure of inst/avg fuel economy and range displays. Got a reman unit through Carquest, 12 month warranty, rebuilt in Canada as opposed to overseas.
Troubleshot this intermittent fault for over a year, replaced MAF/burn-off relays, IAC, MAF, reset idle/TPS, cleaned and rebuilt TB, etc etc. Finally tried the ECM, voila! :cheers:
Troubleshot this intermittent fault for over a year, replaced MAF/burn-off relays, IAC, MAF, reset idle/TPS, cleaned and rebuilt TB, etc etc. Finally tried the ECM, voila! :cheers:
Pro
Joined: Jan 2003
Posts: 573
Likes: 0
From: ALAMOGORDO NM
Re: C4 Idle (mak567)
It's probably the TPS (Throtle Position Sensor). Mine did that a couple of days ago when I changed mine out. When you remove it and re-install it or replace it with a new one you have to either put it on a volt meter or use a diagnostics tester to adjust it. It should be set at 54 milivolts. Mine was set at 130 milivolts. Once I adjusted it my idle went to normal. The Chilton's maunal doen't say anything about the adjustment but when I had my brake boost replaced the machanic pointed it out to me. Good luck and let me know how it turns out. :auto:
