92 SL2 Rough Idle, No Codes

I recently replaced the EGR soleniod in my 92 SL2 to try and fix the
trouble codes 26 and 32 stored on the PCM. I have been driving the car
for three days and no codes have been reset however my car has started to
occasionally idle rough, surge while at a stop light, and seems to coast
like I have cruise control when my foot is off the gas pedal. Any
suggestions as to what could be causing this? Can it be the EGR valve
without setting a trouble code?

 

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?

 

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

<snip>

 

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.