Suddenly Poor Mileage / Minor Cold Running Issue

[elemgee]

Over the last 500 miles or so, the gas mileage on my 94 SVX has taken a nosedive. I was getting around 21, 22 mpg, and all of a sudden I'm getting around 15 - 18 mpg. I live in Delaware and while its been cold here, its not been unusually cold.

Also, when I start the car 1st thing in the morning, the engine will rev for a second at 300 rpm, almost like its going to cut out, and then settle down to maybe 1000 rpm. It seems to run fine when cold, except that when I come to a stop, the revs will momentarily go way down and the car will feel like it wants to cut out, and will occasionally do so. The car runs and idles fine (around 700 rpm) when warmed up.

I checked the engine codes and its showing a code 56 - EGR system, but I dont recall the check engine light coming on while I've had the mileage problem. If it has come on, its intermittent. Also, FWIW, I've replaced both O2 sensors and have cleaned the MAF sensor with a spray designed for that sensor.

I'm not familiar with the EGR system, where things are, etc, so if any proposed solutions pertain to replacing or cleaning any part of that system, I'd need some specifics.

Any help you can provide would be appreciated. Thanks.

Larry