Vacuum leak only at high temp.

[heavyD]

My car idles at 750 rpm solid all of the time unless the outside or underhood temp. gets really warm, then it goes up to 1000 rpm. I'm assuming I have a small vacuum leak somewhere that only arises under higher temps.

I have checked the vacuum hoses thoroughly and can't seem to find a leak. Does anyone know a place that I may have overlooked?

 

[Doug99RS]

Typically a true vacuum leak will not come and go. Unless somehow there's a manifold gasket or something that leaks only when the two metals it seals expand and contract. But I really don't buy that myself.

If you're going to hunt a vacuum leak you may want to buy some carb clean or brake clean and spray it at every seal, joint, and gasket associated with the intake system. Frequently a leak can be detected because the idle will change when the cleaning agent gets sucked in at the point of the leak sometimes enough to cause the vehicle to stall out.

It may be egr related. If you have a vacuum pump you may want to hook a line up to the egr valve diaphram and apply vacuum to it while the car is running. This will cause the valve to open and the vehicle will stall out. Also spray the cleaning solution on it. If it's partially open then the stuff will get sucked in and stall or cause a poor idle again.

I'm kinda leaning away from a vacuum leak unless it's egr related. It just doesn't make sense that it comes and goes. I would suspect sensors or something else.
Doug