Fargw

Also, where will I find the temperature sensor you referred to? Thanks.

I appreciate the info, I'll check this and see what I come up with. Any thoughts on the catalytic converter.

Just bought this truck from a friend and trying to figure out what the problem is. Before I bought it, it was a 2 owner truck, all service records and meticulously maintained. 1 blown head gasket about 10 years ago and about 4 years ago a cracked head which was professionally replaced with a brand new one from a company somewhere in Florida. Just recently he started having this problem with it not starting after it was driven a while. After it sat all night it would start right up. Then this fast idle problem arose. Sometimes it will idle down within a few minutes and sometimes it doesn't. Then there's the issue with what he described as black carbon smoke from the exhaust every now and then. No burning oil, no blow by good compression, no check engine light, normal operating temperature. There is an exhaust leak. Both coils have been replaced, new cap, new wires, new plugs. When the new head was put on, he was told the timing chain and gears were in excellent condition. I'm suspecting a bad cat due to antifreeze getting in it when the head gasket went and during the cracked head episode. Running rich is most likely adding some raw gas to the cat as well. Also suspect a faulty EGR causing the idle issues and maybe the carbon smoke. Not by any means sure though, I'm a welder by trade, not a mechanic. Especially on anything with a computer. This truck is way too nice to let it waste away, as close to pristine as a 30 year old truck can be. Would appreciate some guidance from someone who knows their way around this year and the z24 engine. Thanks in advance.