I've been trying to figure out a rough idle problem and I'm at a point where I'm leaning towards the EGR valve or the EGR solenoid or vacuum lines to the solenoid. I had bought this car with the rough idle problem and the previous owner had just replaced the head gasket, so all the vacuum lines were removed when the head gasket was replaced.
I'm wondering if the vacuum lines, might have been replaced incorrectly on the solenoid, so if anyone out there with a 1993 4.0 jaguar engine and could take a picture of their EGR solenoid and the routing of the vacuum lines, I'd appreciate it or lead me to a site that shows the vacuum line routing diagram. There appears to only be 2 lines on it, if they were crossed, maybe it might make it run rough.
Also, should I have vacuum at idle into the EGR valve, cause I don't. It also seems like I don't have any when the rpms are raised. When should the vacuum turn on thats going to the EGR valve. Thanks in advance.

 

The EGR valve should not be on at idle or W.O.T. It is supposed to work at cruising speeds only. I had a non functioning EGR valve on my 93 XJS, a vacum tester pump would not get it to operate. I replaced my EGR but I was not getting any vacum from the solenoid. I tested the solenoid from a 12 volt source and it clicked so I knew it was working but it would not work when I revved up the engine. A forum member on here informed me the solenoid only works when the car is in gear! I guess you need a lift or at least the rear wheels off the ground to check for power at the solenoid. The solenoid is a simple switch with vacuum from the intake manifold on one side and another vacuum hose going to the EGR valve. When the solenoid is energized it allows vacuum to be applied to the EGR valve. Most EGR valves are also temperature controlled, they don't operate until the engine gets to a certain temperature. The engine computer controls the signal to solenoid

 

Scotlad, With that explaination of the EGR operation, I would guess that if it doesn't operate (open or close) at idle, it should not have any effect on the rough idle running either way.

 

What you don't want with an EGR valve is one that is partially open because of carbon deposits, a weak return spring or a seized rod. These valves live in a pretty harsh environment and they are 20 years old. The mechanical condition of the EGR has to be checked before deciding if it is getting vacum. This may not be your idle problem but it is worth a shot. Have you tried hooking up vacum gauge to the intake manifold and observing the needle fluctuation?