Idle problem cont. May have found solution...
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
Idle problem cont. May have found solution...
NEW INFO IN POST #5, PLEASE READ!!!
Thought I had it; Now see post #8.
Update 7-15, still haven't got it!
*NEW* interesting info in post #25. Still stumped!
Mechanic said timing is very advanced, pulled it down to 10 degrees advance and running great!
I did some searching around today and came upon a thread where a members car wouldn't idle when cold. After a while, he finally ended up replacing the coolant temp. sensor, and that fixed his problem.
I too have experienced the same thing, I've done as many adjustments as possible, but could never get it to run good cold. Today, I ohmed the CTS, it read 220 with the coolant temperature being approx. 175; this isn't right.
I've bought a new one now, waiting for it to cool off before I install. I've got my fingers crossed!
Thought I had it; Now see post #8.
Update 7-15, still haven't got it!
*NEW* interesting info in post #25. Still stumped!
Mechanic said timing is very advanced, pulled it down to 10 degrees advance and running great!
I did some searching around today and came upon a thread where a members car wouldn't idle when cold. After a while, he finally ended up replacing the coolant temp. sensor, and that fixed his problem.
I too have experienced the same thing, I've done as many adjustments as possible, but could never get it to run good cold. Today, I ohmed the CTS, it read 220 with the coolant temperature being approx. 175; this isn't right.
I've bought a new one now, waiting for it to cool off before I install. I've got my fingers crossed!
Last edited by cwyates4; Jul 26, 2008 at 03:32 PM.
Le Mans Master
Joined: Feb 1999
Posts: 9,948
Likes: 40
From: South Carolina
St. Jude Donor '03 & '05
If you have no codes, check you IAC. Doesnt matter what year up to 93, as most IACS were the same till 94 or 95. Then the pins location was a little different due to plug change, yet same function and GM still has no codes for it. It WILL not give any codes when bad and will directly affect idle, especially cold as you get no input from IAC, yet warm your O2's will help adjust mixture.
http://shbox.com/1/iac2.jpg
This guy has a wealth of Knowledge.
http://shbox.com/1/how_tos.html
http://forums.corvetteforum.com/show...light=Idle+IAC
http://shbox.com/1/iac2.jpg
This guy has a wealth of Knowledge.
http://shbox.com/1/how_tos.html
http://forums.corvetteforum.com/show...light=Idle+IAC
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
I'm not getting any codes, but the idle air control valve is brand new. It was one of the first things I replaced when I got the car, so I know its good. I also cleaned the tb, and iac housing while at it.
A while back ago (3-4 months), I used to throw a code 34. After following the trouble shooting guide to that code, I found nothing, couldn't make it come back on for weeks. I wonder if my MAF or the burn off module is bad...
A while back ago (3-4 months), I used to throw a code 34. After following the trouble shooting guide to that code, I found nothing, couldn't make it come back on for weeks. I wonder if my MAF or the burn off module is bad...
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
Hmm...If I disconnect the est (electronic spark timing) connector, the car runs perfect??? It sets a code 42, but runs as smooth as the vortec 350 in my tahoe. 
I'm just trying to figure out how that would make it run so perfect. I can only guess that means my timing is way off or an ignition component such as the icm or cap/rotor is faulty.
I'm just trying to figure out how that would make it run so perfect. I can only guess that means my timing is way off or an ignition component such as the icm or cap/rotor is faulty.
Last edited by cwyates4; Jul 13, 2008 at 02:56 PM.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
esc
I have an 86, and it was hunting, and dying, and popping. when I disconnected the esc while running, it threw a code, and ran fine. I changed it, and it hasn't come back in 2 years.
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
Ok, I robbed the electonic spark control module off my '87 L98 T/A. I plugged it up, plugged the timing wire back in, and fired it up. It ran good initially and it was even cold. I took it for a drive, and noticed roughness again.
Got home, let it cool off. Started it up, put it in gear, and it died, just like it used to do.
So now I'm stumped again. I'm thinking the timing could just be that off, but I'm really shooting in the dark here.
*With the timing wire connected, it swings in idle and runs rich. With it disconnected, it runs really steady and does not smell rich at all.
Anybody?
Edit: Just looked at autozone, they have a different part numbers for the ESCs in the 87 T/A and the 85 Vette. Now I took a step back again, maybe it is the esc.
Got home, let it cool off. Started it up, put it in gear, and it died, just like it used to do.
So now I'm stumped again. I'm thinking the timing could just be that off, but I'm really shooting in the dark here.
*With the timing wire connected, it swings in idle and runs rich. With it disconnected, it runs really steady and does not smell rich at all.
Anybody?
Edit: Just looked at autozone, they have a different part numbers for the ESCs in the 87 T/A and the 85 Vette. Now I took a step back again, maybe it is the esc.
Last edited by cwyates4; Jul 13, 2008 at 08:53 PM.
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Le Mans Master
Joined: Feb 1999
Posts: 9,948
Likes: 40
From: South Carolina
St. Jude Donor '03 & '05
I'm not getting any codes, but the idle air control valve is brand new. It was one of the first things I replaced when I got the car, so I know its good. I also cleaned the tb, and iac housing while at it.
A while back ago (3-4 months), I used to throw a code 34. After following the trouble shooting guide to that code, I found nothing, couldn't make it come back on for weeks. I wonder if my MAF or the burn off module is bad...
A while back ago (3-4 months), I used to throw a code 34. After following the trouble shooting guide to that code, I found nothing, couldn't make it come back on for weeks. I wonder if my MAF or the burn off module is bad...
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
You lose you spark advance when EST disconnected so would appear something is pushing the advance up.Usually when EST disconnected engine will run slightly rougher
Melting Slicks
Joined: Jan 2001
Posts: 2,940
Likes: 5
From: Chesapeake VA
Here is what happened. The harmonic balancer had begun to slip. In looking back at my eariler photos, I can see that, but at the time I did not know what I was looking at. The balancer got worse until it had moved back against the timing chain cover and made a squealing noise from contact. After I changed the balancer, I checked the timing and found that the engine's base timing was just over 13 degrees. On the old balancer it was showing 6 degrees at the same engine position (the last time I set the timing, before the balancer had slipped completely). Resetting the timing to the correct 6 degrees caused a massive improvement in my engine's idle quality and cured the stutter/stumble problem.
I took some phots of the replacement, you can see them here:
http://members.***.net/effergyvette/..._balancer.html
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
I guess thats a possibility, sounds like a rare occurance though. I ordered a new electronic spark module today. I'll put it in tomorrow when I get it and see what that does. If that doesn't do it, then a timing check/adjustment will be done.
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
Hmm...Looking at the distributor, it appears the timing has been retarded a fair amount. I know it is supposed to be pretty much squared up, but mine has been turned clockwise a noticeable amount. I have a picture of my engine 2 years ago showing the distributor squared up with the engine, and it ran GREAT back then, never missed a beat.
Wonder if this could be my problem...? Hope so, easy fix!
Wonder if this could be my problem...? Hope so, easy fix!
Melting Slicks
Joined: Jan 2001
Posts: 2,940
Likes: 5
From: Chesapeake VA
Do you have a timing light to check the engine timing?
If the timing mark is reading 6 degrees (or close to), but moving the distributor to where it was 2 years ago helps the problem, then I think it may warrant a closer look at your balancer.
Keep us informed.
If the timing mark is reading 6 degrees (or close to), but moving the distributor to where it was 2 years ago helps the problem, then I think it may warrant a closer look at your balancer.
Keep us informed.
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
Ok, today I moved the distributor close to square, reconnected the est wire, and plugged in my new esc module. Cranked it, ran for maybe a second, then died. Same thing on second try. Unhooked est wire, started and ran, but not perfectly smooth like before. Pulled some timing and it idled better. Plugged est wire back in, and it turns rough. While driving it, it stalled coming up to a light. It did have better throttle response though, due to the advanced timing, but idle was pathetic.
SunCr, I like that idea, but this is the first time I've messed with timing, so you'll have to tell me exacltly what to do and what I'm looking for.
I'm planning on setting timing exact tomorrow with a timing light and reseting base idle, if that doesn't do it, its off to the mechanic again. That'll start with a compression check and leakdown test, to hopefully eliminate a headgasket issue, piston ring or piston issue, valve issue, etc.
That balancer is begining to look pretty suspecious though...
SunCr, I like that idea, but this is the first time I've messed with timing, so you'll have to tell me exacltly what to do and what I'm looking for.
I'm planning on setting timing exact tomorrow with a timing light and reseting base idle, if that doesn't do it, its off to the mechanic again. That'll start with a compression check and leakdown test, to hopefully eliminate a headgasket issue, piston ring or piston issue, valve issue, etc.
That balancer is begining to look pretty suspecious though...
Le Mans Master
Joined: Jan 2003
Posts: 5,858
Likes: 7
From: Santa Maria CA
I guarantee those test are not necessary. If it where any of those parts, it would not smooth out with EST unplugged. It would be doing it all the time. You need to check the timing with a timing light to see where it's at, and check for a slipped damper. Otherwise you're working blind.
Le Mans Master
Joined: Jan 2003
Posts: 5,858
Likes: 7
From: Santa Maria CA
You're working backwards. You should have checked the timing first.
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
Well, I got it running perfect, except the est wire was still disconnected. 
I went and talked to the mechanic today. He suggested plugging the wire back in and unplugging the knock sensor. If it runs perfect like that, chances are the sensor is bad or it is picking up a false knock. Seems logical to me.
I guess what's going on here is that the timing is, maybe not perfect, but acceptable. When the wire is plugged in, the computer, for whatever reason, is advancing timing like crazy. I can't even get it to run with the wire plugged in and the engine cold. Wire off, perfect.
I'll let y'all know how it goes.
I went and talked to the mechanic today. He suggested plugging the wire back in and unplugging the knock sensor. If it runs perfect like that, chances are the sensor is bad or it is picking up a false knock. Seems logical to me.
I guess what's going on here is that the timing is, maybe not perfect, but acceptable. When the wire is plugged in, the computer, for whatever reason, is advancing timing like crazy. I can't even get it to run with the wire plugged in and the engine cold. Wire off, perfect.
I'll let y'all know how it goes.