is there a problem?

[CJFusco]

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?

[TheCooler]

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.

[SoCal Driver]

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.

[Gordon Rankin]

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

[CJFusco]

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?

[Texas944]

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.

[TCMdocs944]

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

[Texas944]

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

[Brando]

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.

[AFJuvat]

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