is there a problem?
 

I'm trying to figure out here if there is something wrong with my car. Anyhow, here are the symptoms:

when the car has been sitting for a long time (6+ hours), and is started, it runs a little rough for the first minute or so. RPMs are as low as 750-800. If you rev the engine during this first minute, the engine stumbles a little bit, almost as if the necessary gas isn't getting to the engine. Once the engine warms for about a couple of minutes, the RPMs increase to about 900 and the engine smooths out and runs fine.

When driving on cooler, dryer days, the car has a VERY noticable performance advantage than hot and humid days. Driving the car at 12PM when it is muggy out and 12AM is like driving two different cars.

So... any ideas?

O2 sensor possibly? Have you gotten emissions done yet? Uhm...maybe you wanna check the pressure in the fuel rail to make sure its fine also.

Idle control valve.

Hot and muggy suggests to me that you have the A/C running.

I've always found a car to be a better performer after a wash and wax.

When did you last do a tune up on your car? Check plugs, cap rotor and air filter. Little stuff first..

SoCal - no, i don't have the AC running, i'd always rather have the sunroof off.

Gordon - I just changed the cap and rotor about a month ago, an oil change about a month and a half ago, air filter was "recharged" (K&N) about 3 months ago... new plugs were done last fall, and I have an extra set at my house, so i can replace them tomorrow if I want.

Cooler - I haven't had Emissions done yet because... well, I'm sure you've heard about all the trouble that CT has been having with their testing stations.

So how would I check if the idle control valve and/or O2 sensor were malfunctioning?

Usually when an idle air control valve is going out your car will want to stall when you pull up at a set of lights - not from starting - but with these Porsches, i have come to expect the opposite of normal - you can take it out and check to see if it is varnished up - clean it out with some carb cleaner. Same for the O2 sensor - take it out and soak it in carb cleaner overnight - blow it out real good with compressed air. I would tend to go with The Cooler and check fuel pressure - watch the gauge while someone cranks it to see what you are getting at the start.

I thought the O2 sensor was not supposed to be cleaned or cleanable without affecting its function?

when they cake up, sometimes they can be cleaned - you got about a 50/50 chance of it working (from experience)

Possible: Your K&N air filter is pulling in ripe hot air off of the engine block. On cold days you would notice a difference. If you need a stock airbox i have one lying around.

For the stumbling problem - look for a leaking injector.

All of these cars like cooler and dryer days - air is denser with low humidity - perfect for a car.

Chack your air flow sensor - you may have a bad or fouled air temp sensor.

AFJuvat