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Rough Cold Idle Fixed

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My 99 C2 cab with about 60K miles has been having issues with a rough cold idle. Once warm it smoothed out. Lately, the cold idle was getting more ragged. I've been going down the list of usual suspects. New filters, cleaned MAF, cleaned ICV, cleaned throttle body. None of these made much of a difference. After searching the forums, I was convinced it was the oil separator bellows. I went underneath and inspected the bellows. No sign of cracks or other wear. Not a single drop of oil around it. I decided to leave it alone. Searched some more. I found a thread in which someone suggested it might be an ignition problem, specifically one or more bad coils. I read some more about coils and the more I read, the more I thought this might be the source of my problem.

As I was due to replace spark plugs for my 60K, I ordered six new coils in addition to plugs. Based on what I was reading it's best to replace them all when one goes, so I went ahead and bought six. I'm glad I did. I did the plugs today and found two coils had significant cracks and two more had faintly visible hairline cracks.

After 'rebooting' the DME I fired her up and was absolutely floored by the difference. It idled a little fast as the DME sorted things out but quickly settled into a smooth healthy idle even though it was stone cold and hadn't run in four days. I let her idle for several minutes while putting tools away. I then took her out on the road and it was sweet. Best it's run since I've had it. :clapping:

Thanks to RennTech for the archived info! :renntech:

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