1990 Mercury Grand Marquis

~83K miles. Starts great. After a few minutes, idle gets rough. Can't hear any vacuum leaks, no "check engine" lights on. Bought one of those plug in engine testers. That tells me the EGR may be malfunctioning.

Questions...what exactly does the EGR do, route some exhaust back to the engine to burned again, right? Could a malfunctioning EGR cause these symptoms? Thanks in advance.

Gary in NC

My 1983 grand marquis has had problems with the EGR valve; every once in a while a carbon deposit will build up inside it, and eventually gets big enough that it holds the valve open. What ended up having to be done (each time this happens) was take the vavle off, and use a vacume pump to open it fully, and then blow the build-up out of the valve with an air compressor.

I haven't actually had this problem in probably a couple of years. Every once in a while, I'll get out on the highway and run the throttle wide open, with the intent to blow out any small deposits before they get large enough to cause trouble.

I don't know if this actually helps.... but I like to think that it does :-D

I'm kind of a lead foot anyway....oh well.

But like Mr. Moats said, there are a number of things that can cause a rough idle.

Nic