92 SL2 Rough Idle, No Codes

Sounds like a vacuum leak.

I just drove the car again and noticed that when the car is decelerating the gears seem to shift a little rough (I have an automatic) and if I take my foot off the gas pedal at around 10-15 mph the rpm doesn't change and the car just coasts at the same speed.

I was sitting in the driveway with the car in park and the engine was idling around 1000-1100 rpm. Once the engine cooling fan kicked on the rpm dropped to around 600 and the engine seemed to be running as it had before I did anything to it. I checked the vacuum hoses and couldn't find anything leaking. Thanks for anyones help in advance.

Or maybe a stuck EGR valve?

I thought that but I couldnt remember how exhaust gas effects the idle. It might even be trying to re-learn idle control.

From the Chilton's I've scanned, a stuck open EGR valve will basically cause everything to go wrong. A stuck closed one causes you to fail the smog test.

As a quick aside, anyone know what that funny pump thing under the driver's side area of late model Trailblazers is? It's near the ABS (?) pump, but has two thick hoses going off to the engine somewhere. I'm guessing it's an electric smog pump of some sorts?

basically

If the EGR is stuck open, the engine can't create enough vacuum for the engine to start easy or run at idle very well. Huge vacuum leak at that point.

Ken

Thanks everyone. After a couple empiric tests, it seems that the EGR valve is stuck open. Just put an order in for a new one.