What would cause a 1995 GMC Jimmy to idle and run rough and the check engine light come on?

Answer 1

Mid 90's Jimmy's have issues with cracked blocks, at transmissions, the front differencial, as well as the oil: pan, filter, pump, and gasket. It is very possible that the block is cracked.

AnswerIt could also be carbon in the EGR valve... AnswerEarly 90's Jimmys has a multiport fuel injection system which used a fuel regulator and delivery system inside the intake maniford. The Central Port Injector(CPI or Spider) has had a tendency to leak from the regulator putting excess fuel into one side of the intake manifold. The single O2 sensor reading the combined exhaust trys to lean the mixture by shortening up the "on" time for all of the injectors which leans out the other bank of cylinders. In essence you have three cylinders running rich, three running lean. Not the best situation for a stable idle.The indication of this is that one side of the intake manifold will be relatively clean(usually a yellowish brown)from being cleaned by the gasolene, and the other side dirty from the blow-by products from the crankcase vent. Check out: http://www.asashop.org/autoinc/feb2000/techtotech.htmfor a expert diagnosis from an ASE Certified Tech with lots of pictures of what I was trying to explain. Look for "Jimmy CPI Unit" on EBay, they have some of the newer modified units for fairly cheap ($200), their not hard to change, just be careful not to get any dirt into the injectors when you remove the poppet valves at the end of each feed tube. That's about it if it's the CPI, hope it helps.94 AnswerI have gone through 2 EGR ValvesA few times a friend even cleaned one to get it going, It worked for a while but eventually failed. Answerits prolly the egr valve a piece of carbon is prolly holdin it open mine used to do that but i got a gasket made by timeco an it has a screen that stops the carbon from buildin up AnswerIf the check engine light is on, get an obd2 scanner and check out what code is stored in the computer. The scanner will tell you what codes showed up even if the light is now off. The code should tell you exactly what is wrong without guessing.