Surging Idle when Hot Outside
 

The idle on my e-gas S surges between 600 and 1000.

When its cold outside, the idle is steady. The hotter it gets the more the surging occurs. For example, the idle is rock steady at 50 degrees. At 80 degrees, it's moving up and down between 600 and 1000 every few seconds. It will seem to steady up at 700, drop to 600, pop up to 1000, resettle at 700, and then start the down-up cycle all over again.

Any idea why this might be happening? Most importantly, why does this dependent on outside temperature? The MAF is new. It was happening before and after I replaced the MAF.

Thanks

There's wealth of info/lots of threads here. just search and read them to see if any relates to your car. Here's what I did.
Three years after I purchased the car (used 01 5 spd back in 2006) from Porsche dealer and with certified used car warranty, it started to idle rough. not ambient temperature dependent (Southern Cal is always summer) and dropped to 600, burped to about 900 rpm. before this, the idle was rock steady at 700.
I did the MAF cleaning, fair result but did not really cure the hunting.
Following another thread, cleaned the throttle body. The throttle body at the butterfly was really dirty and had built up a ridge of black goo. So for my car, the combination of MAF and throttle body cleaning did the job. It was not a vacuum leak.

you may want to test for degrading AOS and also wiggle the hose coming out of the AOS and into the manifold behind the throttle body for leaks
good luck