Rough Idle on 92 Passat 16V

I need some help determining what is causing a rough idle in my Passat Wagon '92, 16V. It only occurs when there is high ambient temps or the engine is at the upper end of warm. This does not occur at low ambient temp or on initial start up.
Thanks for anyone's suggestions

That system can be difficult to diagnose as it requires special gauges & test harnesses. You can remove the rubber boot from the top of the air flow meter & clean off any oil deposits. If you have a multimeter you might want to check the coolant temp sensor located in the upper radiator hose flange to the cylinder head. It should read about 2-3000 Ohms cold & go to about 2-300 Ohms at operating temp.