Scratching my head on this one. I have a 1997 Camaro with the LT1 350 engine. When the outside temp is below deg. F. or so the car idles rough until it warms up. I cleaned the ICS pintle and throttle plate and ran fuel system/injector cleaner/top end decarbon stuff through it and no change. Press on the gas just a little and when the rpms come up, it smoothes out. The car had new plugs and wires 30,000 mi. ago and since there is no mis under acceleration at all, I'm not thinking ignition anyway. As soon as everything warms up, the problem goes away. Put up with this most of last winter and it went away all summer. Anybody got any ideas?
Rough Idle Cold
- Thread starter johnd
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Leaking PCV valve or EGC valve. Open vacume line
yes, or could be dirty MAF (easy to clean), clogged fuel filter, clogged air filter, maybe O2 sensors but i think they're not that important during warm up, or...the dreaded Optispark but don't think about that until everything else is addressed first
spray out the MAF wires with electronic parts cleaner and check all connections you see electrical, vacuum, etc
spray out the MAF wires with electronic parts cleaner and check all connections you see electrical, vacuum, etc
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another thing i've seen is corrosion on the main contacts under that red plastic junction box. i took em apart (disconnet battery first!) and used fine sandpaper to clean em up. remember how they stack up and replace, that helped a stumble i had once
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ACT and ECT checks should be performed too.
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From the symptoms you describe, it most likely isn't a broken motor mount but doesn't hurt to check it while you are at it. You never know.
I think I found the problem last night and it is a head scratcher. I put my hand on the alternator and the roughness appears to be coming from there. When it is doing this, I can rev. the engine and feel the alternator heat up under my hand which is odd. Since the voltage on the gauge is about 14, I don't think it is overcharging which kind of points to a possible internal short in the alternator. I need to remove the serpentine belt to verify that the roughness is really coming from there and check the output current to see if excess current is internal or external. This was really a new one on me.
Only when cold?
Could be a coolant sensor.
If it is the alternator, it is an oddball problem , for sure.
Could be a coolant sensor.
If it is the alternator, it is an oddball problem , for sure.
Originally Posted By: johnd
I think I found the problem last night and it is a head scratcher. I put my hand on the alternator and the roughness appears to be coming from there. When it is doing this, I can rev. the engine and feel the alternator heat up under my hand which is odd. Since the voltage on the gauge is about 14, I don't think it is overcharging which kind of points to a possible internal short in the alternator. I need to remove the serpentine belt to verify that the roughness is really coming from there and check the output current to see if excess current is internal or external. This was really a new one on me.
Wow that's odd. Could it be a bearing in the alternator is going? Just bad enough to cause a little roughness in the engine, yet not bad enough to seize up and ruin the belt, yet?
I think I found the problem last night and it is a head scratcher. I put my hand on the alternator and the roughness appears to be coming from there. When it is doing this, I can rev. the engine and feel the alternator heat up under my hand which is odd. Since the voltage on the gauge is about 14, I don't think it is overcharging which kind of points to a possible internal short in the alternator. I need to remove the serpentine belt to verify that the roughness is really coming from there and check the output current to see if excess current is internal or external. This was really a new one on me.
Wow that's odd. Could it be a bearing in the alternator is going? Just bad enough to cause a little roughness in the engine, yet not bad enough to seize up and ruin the belt, yet?
another thing i remember from my LT1 camaro is the coil wire was corroded, but that was worse than a stumble and did not go away at higher rpm
the short coil wire to optispark had the green fuzzies. replaced and back to normal. also replaced the stock coil w/ the yellow Accel coil
also the IAT and even the MAP sensor are easy to change and cheap. don't know how many miles you have
the short coil wire to optispark had the green fuzzies. replaced and back to normal. also replaced the stock coil w/ the yellow Accel coil
also the IAT and even the MAP sensor are easy to change and cheap. don't know how many miles you have
I borrowed a current probe and a battery tester load. The alternator will drive 100 amps according to the probe when I throw a load on it, so I think it's function is ok. The IAT sensor is one that hadn't occurred to me. Since the problem is quite temperature dependent it is a possibility. I'll check it out. While I have the scanner on, I'll verify the coolant temperature sensor function but since it starts ok, I don't think this is a problem-hard starting is a symptom of a non-responsive CTS.
Intake air temp sensor seems to be fine. I put the car on the Autotap scanner this morning before I left the house and it had a normal reading. No pending codes either. It was 73 deg in the garage and the idle was as smooth as could be. I'll do another when the temp is below 60 and the problem returns.
Problem solved. The battery was sufficiently shot that it took too much current to charge it. Load test revealed 350 cold cranking amps and it should have been 650. Replaced under warranty. The thing was only 15 months old.
I'll bring this thread back from the dead in hopes that somebody might find the final solution interesting. The alternator was squirrley but that wasn't the whole problem and replacing it helped a little. I pursued all other sorts of things to no avail but this morning I got to thinking that it almost seems like an unbalanced something but what on earth could be temperature dependent. The computer miss counter shows nothing so it wasn't a problem with how the engine was running. It occurred to me that I had an aftermarket harmonic balancer which I put on a few years ago. I put a heat lamp on it and the vibration problem went away as it warmed. Apparently it is an issue with the rubber compound and it's ability to flex below a certain temperature. This was a tough one but I think I have finally found it.
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