My 91 305 TPI sometimes idles too high. It's intermittent. Sometimes it's around 1k and sometimes 1600-1700. Once the engine cools down for awhile it idles fine again for awhile then the problem repeats. I pulled codes 32 and 33. EGR & MAP. EGR checks out fine and I have and extra MAP sensor that didn't solve the problem.

Poking around under the hood looking for vacuum leaks or anything blatantly obvious, I hear a sizzling coming from the the intake manifold right around the area of the alternator. I just got this car a few weeks ago and it looks like a previous owner tried to smear some RTV in the area I hear the noise. It's obvious that the intake manifold gasket is leaking here. But I would assume that my idle would be low and the engine sluggish if I was sucking air at the gasket...but in my case it's idling very high. It's a no brainer that the gasket will need replaced but could this be causing the high idle too?

 

Yes! an intake leak will cause a high idle and mess with the MAP reading. Get that fixed!

 

Dove in head first.

 

A good time to clean the intake, plenum and runners...followed by a coat of paint.