The first thing I would do is drive the car to Autozone.They will connect a scanner to your diagnostic port to see if you have any codes present.The check engine light doesn't have to be on in order for a code to be present.If codes are present,they will usually tell you which sensors or components are faulty or it will give you a good place to start your trouble shooting.A defective pcv valve,clogged or leaking pcv hoses can cause cold start rough idling or stalling.A dirty or defective egr valve can also cause the same.The egr valve should not be functional during cold starts while the vehicle is warming up.If its stuck open or leaking,it will cause a lean fuel mixture which equals rough idling.The vehicle must be placed in gear before the egr valve will work.This is when your problem is occurring too,when in gear.The iac(idle air control)valve is responsible for idle regardless of whether the engine is cold or warm.You can remove it and clean its passages with carb cleaner.

The problem is YOU and your OIL CHOICES! WHAT's happening is that your IDLE AIR CONTROL VALVE and THROTTLE BODY are junked up with BAD oil sludge, tar and COKE! VALVOLINE may NOT be used in a SAAB turbo! It will MELT the turbo bearings up! MOBIL ONE 0W-40 is ONE oil that id\s GOOD for your SAAB< and after GM cheapened them down, you may need a few3 things CHANGED BACK! Like the WATER PUMP and TIMING BELT! ANYWAYS! get a FULL MOTOR FLUSH and then have your T body and IAC valve cleaned up! BAD OIL makes LOTS of acidic vapors and TARRY GO that jams right into engine sensors. AS a REAL SAAB technician, i worked to get VALVOLINE out of their dealership! EURO oil is DIFFERENT and more PRICEY to refine! IT will NOT slump up, make SLUDGE or TAR< or even any ACIDIC vapors! The IAC adds more AIR to what your FOOT requests to keep engine from stalling and to keep IDLE air/fuel mixture in a proper range! Once BAD OIL makes tarry deposits, ti RUINS idle and starting too! I would use ONLY TOTAL ENERGY oil from France, or RAVENOL< or PENTOSYNTH oil in it! PENNZOIL ULTRA EURO is ALSO a great bet! BYE NOW!rgmuske@yahoo.com

With a car this old it could be any number of things. How many miles are on the engine? When was the last tune up, (not oil change), meaning when did you last change the spark plugs, wires and coils? is the original Idle control valve still inthe car? Is the original MAF sensor in the car? (Mass Air Flow).

Basically you don't want to just blindly throw money at the car because you don't know the specific faulty part or parts. Just that it stalls. So you are going to have to take the car to a shop, leave it over night so the tech can start the car up cold and see the symptoms and then run diagnostic tools on the car to see where the fault might lie.

IAC valve passage or throttle plate is dirty. At least those are the most common. Before you get out the carb cleaner you better find out if either have a coating that will be disturbed by improper cleaners.

Ok so my 1998 Saab 900 se has an automatic transmission. When I shift from park to reverse, from park to drive, or vice-versa, it sometimes idles roughly or stalls. This only happens on a cold engine. What could be happening?