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Old 06-19-2005, 07:30 PM   #1  
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HIGH Idle

Just to let you guys know I am a mechanic. I'm not very familiar with the non obd II cars. I just bought this 88 IROC (5.0l tpi ) as a toy. too good a deal to pass on. anyway, The idle on this car is very high in my opinion somewhere in the range of 1200 to 1500 rpm on the tach in park. around 1000 rpm in drive. I thought through the searching on this site, it may be 1 of a couple of things. tps, iac, or a vaccum leak. there appears to be no vac leaks although i didn't dig in too far just sprayed carb clean around the intake and lines for rpm change. i've seen many posts on the tps and testing but i,m not sure thats my problem because unless it is bad i don't see how this can just fall out of adjustment. could be wrong though. I cleaned the t/body and iac pintle and no change. Just a little info on this car. very clean throughout, put a battery and some gas in and she fired right up and ran pretty good even the idle was not bad, but then I found this thing had a big hole in the radiator. so needless to say i didn't run it for long. after the rad install i started to see how she would run at normal operating temp. runs very well for a car that sat for a year or more. but now the high idle and I did notice it starts right up and sometimes stalls but once running just the high idle. any ideas guys??
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Old 06-19-2005, 08:10 PM   #2  
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Re: HIGH Idle

Hmm... Definitely go through all your vacuum lines and make sure there are no cracks, dry rot, etc. I'd also check your accelerator pedal/linkage and make sure nothing is gummed up or hanging up. Try unplugging the IAC and see if the high idle goes down. Then plug it in and see if it shoots back up. Id imagine if it goes down then shoots up again, something is up with its operation. Never tried that idea, so maybe it would work, maybe not. Good luck, and welcome to the board! Oh and check the EGR operation, and let us know if there is a SES light on, or any codes in the history. To pull the codes, locate the ALDL under your drivers side kick panel area by the center console. There should be a black cover over it. Jump the top right hand last two pins. Then turn the key in the on position. Count the number of blinks the ses light emitts. For example, you should first get a code 12. It will blink 1 time, pause for a second or two, then blink twice. It will repeat this code 3 times in a row then move onto the next trouble code. If no other codes are present than code 12 everything is kosher as of now with the computer detecting any faults. Code 12 is normal. Don't worry about it. Good luck!

Last edited by Pneumatic_Tire; 06-19-2005 at 08:14 PM.
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Old 06-19-2005, 08:29 PM   #3  
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Re: HIGH Idle

Thanks pneumatic, I will pull the codes with my scan tool tomorrow, its at the shop. no ses light. the egr operation could be a problem. I should have thought of that. I will take a look. the scan tool is my best friend you can see tps volts, egr state, iac steps etc. just need to get to work and take it home tomorrow. I hope once I know more about these 3rd gens I can help you guys with any tech questions. I'm a jeep/chrysler tech by trade but gm's have always been my game.
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Old 06-19-2005, 11:14 PM   #4  
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Re: HIGH Idle

If the IAC isn't done just right it won't work. The computer has to know its being adjusted from what I was told, otherwise it won't recognize the changes. There's a tech artical at thirdgen.org. Also, does the 1000rpm in park vary or is it strictly the at 1000? Mine stays at 1000, charges a bit, then drops to 700-800.
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Old 06-20-2005, 09:44 AM   #5  
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Re: HIGH Idle

I had the same problem with mine and it ended up being the IAC valve. When I took it out of the throttle body I had noticed that it had come unscrewed for some reason. Put a new one in and had no problem after that.
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Old 06-20-2005, 03:07 PM   #6  
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Re: HIGH Idle

Even with a vaccuum leak, a good IAC will pull idle air and retain an rpm around 600-700. The TPS is probably not the problem, but if you want to check it, attach a volt meter to the top and middle terminals and if it reads close to .54 volts at idle then its good. If I disconnect the IAC on my car, the idle goes up to around 13-1400 and stays there, so yours may be disconnected, not getting a signal, or is bad. One of those would be my guess.
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Old 06-20-2005, 05:09 PM   #7  
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Talking Re: HIGH Idle

Thanks for all your help. hey firebird, do you mean the tps needs to be set correctly, you did say iac and from my knowledge the iac cannot be set it either works or not. (true?) as far as idle it stays at 1000 in drive and pretty much stays at 1300 or so in park, very smooth running but idle too high. I haven't tried to unplug the iac to see if it changes but i did unplug the tps and no change. so whith all your help and some of my own diagnosis i think i will start by making sure base timing is correct, then checking electrical feeds to the iac and tps to see if they are working or out of range. I,m sure its gonna be one of the two but I am a mechanic that likes to diagnose things and not just throw parts at it. I'll let you guys all know what the verdict is in a couple of days when i have time to work on this again. thanks again for all the info.

Last edited by camaroken; 06-20-2005 at 05:13 PM.
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Old 06-20-2005, 05:56 PM   #8  
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Re: HIGH Idle

The IAC is computer controlled, but the idle itself can be set through a screw on the drivers side of the throttle body. This MAY be your problem (incorrectly set idle). It seems more like a malfunctioning IAC to me though.
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Old 06-21-2005, 05:33 PM   #9  
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Re: HIGH Idle

I agree 91-z28-l98. I still haven't got to it yet but tomorrow night I'll know more. I'm a little skiddish now cuz i've got a new symptom related to this. I started it today and it seemed to have a miss, which leads me to thing i have other things going on here, like possibly a valve hanging up or something of that nature. idle still high but seems to have a slight stumble in the right exhaust bank when cold and gets less and less the longer it runs, which is why it think maybe a sticky valve or something. hope not, no smoke or anything like that but with the scan tool and some tests hopefully I can get to the bottom of this freaky thing.
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Old 06-26-2005, 11:57 AM   #10  
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Re: HIGH Idle

hey guys, I looked at my idle issues a little more and am getting confused now. well here goes. i haven't had tome to play with the car for a couple of days now. I get in today to move it to the garage and it had the usual stumble stall thing at start up but the seemed to be almost normal. i shut it off restarted and still seemed pretty good. I disconnected the iac and the idle increased as it should. plugged it back in and would not go back to idle.( bad iac you would think) since then did nothing else but I am back to the origional problem. the new and confusing part of this is I would of thought unplugging the iac would set the check eng light, but no. so i rolled the key offf then on and found the ses light is not working. not even the in the test mode key on eng off. hmmm. I may have an electrical problem. any ideas on manually checking this circuit. scan tool unavailable due to work being busy (go figure). also, how to check EGR. gm seemed to want to bury this unit under the plenum.
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Old 07-16-2005, 02:09 PM   #11  
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Re: HIGH Idle

finally back to the-roc. well, cannot probe connector to pull codes. thing i got a bad or disconnected ground there. but i di hook up the scan tool and found 3 codes 2 maf codes and a o2 rich code. noted them and cleared. car ran fine the first couple of times i ran it, then back to the idle problems. codes have not returned after two good trips in the monitor. i think i set the codes by disconnecting things diagnosing. i think my problem is minor but very frustrating. sometimes it runs good other times like crap. where should i go with this?
Just a refresher, 88 305 tpi, iroc, idles smooth but sometimes will not drop below 1500 rpm's at idle in park, different every time i run it.
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Old 07-16-2005, 03:45 PM   #12  
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Re: HIGH Idle

does the SES come on at bulb check?
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Old 07-16-2005, 03:53 PM   #13  
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Re: HIGH Idle

yes it comes on at bulb check and turns off when running, i'm working on it as we speak and just as i started it light came on and stayed on. its running real rich and stumbling all over the place. i shut it down and did some other things to it, started it back up and here is my 1500 rpm again and will not idle, but not stumbling, running as rich no ses light on. haven't pulled it but i gaurantee its gonna be the 02 rich code, black smoke out the exhaust a good indicator. any ideas?

Last edited by camaroken; 07-16-2005 at 03:57 PM.
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Old 12-13-2015, 07:03 AM   #14  
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Re: HIGH Idle? did u get straight my iroc is same way

es it comes on at bulb check and turns off when running, i'm working on it as we speak and just as i started it light came on and stayed on. its running real rich and stumbling all over the place. i shut it down and did some other things to it, started it back up and here is my 1500 rpm again and will not idle, but not stumbling, running as rich no ses light on. haven't pulled it but i gaurantee its gonna be the 02 rich code, black smoke out the exhaust a good indicator. any ideas?[/QUOTE] have u got iroc fix ? my iroc does same thing
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Old 12-13-2015, 09:01 AM   #15  
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Re: HIGH Idle

"camaroken" has not returned to the site in 6 years, so not likely he will reply.

To me, it sounds like a defective coolant temp sensor. If the ECM thinks the engine is very cold, it raises the idle RPM and richens the A/F mixture.
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