update, I drove the car for a few days and after reving it up at startup it would idle fine, after warming up I thought it was going to die at each stop. the idle would drop to about 400 or 500 but then would go up to about 750-800 and idle fine? it did that for 2 days then on the 3rd day as soon as I would stop it would die right away? I had to put it in neutral at every light and keep it at about 1000 rpms to keep it running??? I bought this car used and have no idea if they ever did a timing belt or not, could that have anything to do with it? Thanks.

 

I don't think it's timing related. I think it's either fuel or air. Have you checked the fuel pump for pressure both while running and when just turning on the key? I'm not sure what the psi should be on the car, so don't ask. I guess you could do a search on Google and find that out. Did you check the throttle plate and make sure it's operating properly and not all funkied up with carbon deposits?

 

I hope no one did a timing belt on it, because S cars have timing chains.
Was the EGR valve gummed up?
Throttle position sensors on these cars don't usually exhibit the rpm dip and recovery when they go bad..

A hung up or not fully closing EGR (that should essentially be mostly closed at idle) would pass unburnt fuel into the intake when it's not supposed to, overrichening the mixture dropping the RPMs as if you were flooding it into a stall. Then the front O2 would pick up the overly rich mixture and lean out the fuel coming through the injectors. At idle, the IAC, if hung up or not moving properly, could be the source of extra air entering the intake , further leaning out the mixture to the point that you have to put your foot on the gas to have enough fuel to burn with all the air you might be getting through the stuck EGR and/or stuck IAC.

You could look at those.

Or keep asking questions and ignoring the advice provided.

I may be right -- I may be wrong.
Dunno.

 

Any updates?