Ok. I have a 94 Sonoma 4.3 Vortec. So far I have replaced plugs, wires, cap, rotor, PCV valve, EGR valve, CPI unit. The truck runs great under power, but it has a slight rough idle at times. I picked up some Sea Foam and put some in the fuel tank, ran some through a vacuum line, and put some in the crankcase. The rough idle remains. The vehicle is not throwing any codes. It has 115K on it. Any suggestions as to what may be causing my problem and how to fix it? Thanks

 

How rough of an idle? Like if you come to a stop will it stall out? Could it be the Air Idle control valve?

 

It's not that bad. It won't stall out. It just shakes a bit and the RPM needle with fluctuate between say 500 and 800 rpm. If I had a bad AIC valve would I get a trouble code, as my vehicle is not currently throwing a code? Also, does anyone know if there is a way to test the air idle control valve?

 

I have the same problem with my '93 s10 blazer. Tried and fixed most of the things you did, haven't changed much.

 

I'm about out of ideas as to what is causing it or how to fix it. The IAC valve could be my problem, not sure. It's not bad, it's more annoying than anything. Fuel economy and performance both seem to be fine.

 

My Blazer has had the same problem for the past year, and I still haven't found the answer. Have you noticed any specifics about when it starts to idle rough? Mine does it more in damp or rainy weather - I suspect moisture is getting in somewhere, but I have yet to figure it out!

 

How bout a plugged injector or plugged Cat.Converter? My 90 Beretta had rough idle found out the Cat.Converter was Plugged...