My old Jag is running and idling rough. It's an '02 S-model that I just got, and put 3 tanks of ordinary gas in it before I found out that the engine requires premium. I've since put a tank of premium through it and a couple of bottles of Lucas but no change--it's still running rough. So, do I take it to a mechanic, or continue treating it myself?
Country: United StatesMake: JaguarModel: S-TypeYear: 2002Engine: 3 litre
Hello and welcome back to justanswer.comIs the engine light on or does it ever flash? Does the vehicle run rough all the time at idle or while driving? Is the problem worse when the engine is cold?
The engine light is not on and I have not seen it flash. The condition definitely improves, both idling and driving, when the engine is warm, but still runs rough when I'm going up a hill. It hasn't stalled yet.
Based on your description it sounds like you have a vacuum leak. On your vehicle I see issues with both the upper and lower breather elbows. The top one is easy to see as it is a small 90 degree rubber connector in the back of the intake. The lower one is under the manifold so there is no way to visually check this. I need you to listen for a hiss or air noise from the back of the engine while it's idling preferably when cold. If you do hear this then I suspect a vacuum leak from that breather. Also there are two IMT valves one at the top and one on the side of the intake. There are seals on both that leak. If there are no leaks then it may be a failing ignition coils.
12 years at a Jaguar dealer as technician and shop foreman.