My 1995 Suburban, affectionately known as the Road Pig, is having some rough idle problems that I can't seem to chase down.

I'm looking for any advice on what to look into before I give up trying to fix it myself and take it to someone. I have some local guys that I like, but I'd prefer to learn/diagnose/repair myself.

Symptom: Rough idle, almost like it's got a miss/vacuum leak. Especially noticeable when I put the motor into gear.

What I've checked so far:
- EGR valve is good. It should be, it's brand new. If I depress the valve with the engine running, the engine wants to stall, which means, I believe, that the EGR passages are not clogged (whew). EGR also has vacuum at idle, and can hold vacuum.
- IAC seems to be good. It also looks new. It has about 50ohms on it, which is within spec I believe. The hole appears free of crud, and if I start the engine with the IAC out, then put my hand over the hole, the engine wants to stall.
- Throttle plates appear fully closed at idle.
- TPS has power and ground. I don't have a scanner so I haven't checked the voltage.
- No obvious vacuum problems.
- Cap, rotor, plugs are all new.

What should I look at next? Thanks!

 

you can check the intake and throttle body for vacuum leaks by spraying air intake cleaner around the gasket areas and see if that changes anything. i know from experience that the intake gaskets were bad for leaking,check the back of the intake and if its leaking oil out of the back of the intake,you will need to replace the intake gaskets.leaking intake gasket will give your symptoms like what your having.it could still be some thing else causing your problem,but its some thing to look at.hope this helps.

 

Sounds like you've covered what's often called ground work, just don't have the diagnostic equipment to find the problem. JMHO
David g.