Low RPM idle

The symptoms were low idle RPM, around 500 and I could not adjust the idle speed with the bypass screw. The idle was rough and exhaust smelled very rich. I could throttle up to 1500 rpm and it ran smooth.

I checked all of the vacuum hoses and found nothing bad.
I checked the intake system from the AFM to the throttle body and also found nothing wrong.
I still suspected it was an air leak but did not know what to check next, so I bought a smoke generator from Amazon.



In less than 1 minute after hooking it up, smoke was coming out from under the intake manifold.



After removing the intake manifold I found the problem. The intake manifold gasket was blow out in two places.




I installed a new intake gasket and the truck runs normal again.

I wish I would have got the smoke generator when I started diagnosing the problem, it would have saved a lot of time. This is a great tool for finding air leaks.