You may remember a while back I had an issue with my check engine soon light turning on with my 2000 sl Saturn.
I finally figured out the cause of the High idle speed and cylinder 1 miss fire :)
The intake manifold gasket is totally trashed. This was very hard to diagnose as I never thought a leak in the intake could cause the engine to misfire. I read up on this subject on many forums and someone with the same problem noted that when the ac is on the engine would idle at normal speeds but will run very rough, and that if you spray water and your gasket is bad you should hear a hiss or pop when the water is sucked in.
I tried this test on my car and it hissed and popped a lot with each spray of water, so there was a definite leak in the gasket.
Fist problem I noticed wile removing the throttle body is how much carbon build up there was on everything. There was a good 1/8th inch of gunk on the valve its self .
I was shocked to see the gasket after taking more then 3 hours to remove everything properly and drain the coolant.
I can’t think of any way this could of happened. Was this a bad gasket installed at the factory that got worse over time? Another thing I noticed is that the nuts were all hand tight on the manifold!?!
You can clearly tell on the manifold that there was definite blow by on cylinder 1
I was totally amazed how bad my coolant was .