My 91 4.9 STS has been running crappy at idle lately. I cleaned out the throttle body and EGR tubes inside like someone suggested but it still runs bad. Today the SES light came on and its the E048 code. Can anyone give me some details as to what needs to be done?? Car runs fine at speed just really bad idle for some reason.

Should I just replace the EGR valve or could it be something else. I think they cost about $60 so I want to make sure thats the problem before I go ahead and buy it.

i would check all the hoses related to the EGR first replace any damaged or worn hoses. if they check out, fire your engine up,let her get warm,then locate the EGR valve near the water intake housing (the EGR is the mushroom looking device). take your fingers and press underneith the EGR and see if it moves, if it does, your engine will stumble, and that would indicate that the valve is working properly.if it doen not move at all, then your EGR valve is faulty. if those tests check out, look at the EGR solenoid, follow the little top hose coming from the top of the EGR, to the little vaccume solenoid that the hose will be connected to. make sure the hoses and electrical connections are tight and clean (use some electrical contact cleaner). if all that crap does'nt work, replace the solenoid. if it still runs rough, a tune up may be in order. good luck dude.
:cool:

Are you sure you cleaned the EGR tubes all the way through to the passage below? The tubes are about 1.5 to 2 inches long and need to be cleaned all the way through to the passage below.

You might also search on the forum search feature using "EGR" and read the posts pertaining to the 4.0. There have been some EGR diagnostic steps provided in the past posts. Ignore the stuff on the Northstar as they're different EGR systems.

This is one of the posts that describes the procedure briefly:
http://www.cadillacforums.com/forums/showthread.php?t=13980&highlight=EGR

I have already pulled off the EGR, guess I will put it back on to test it the way you said. It moves but kinda firm I am not sure how it is supposed to feel. There is alot of carbon on the valve part so I will clean that off before I try it again. Also I changed the plugs and wires a not too long ago. The EGR tubes are clean I rodded them out with the throttle body off and was able to get in there and clean them out very well. I just hope all that loose carbon in the intake didn't screw anything up :hmm: .