I have a 2000 S-Type 4.0 and have had an ongoing problem with a rough idle. At times, codes have come up indicating problems with various coils. Each time, I changed the coil but the rough idle continues and the scanner show nothing. I only now realized that when I put it in park and give it gas, the roughness disappears. As soon as I take my foot off the gas, it returns. This leads me to think this issue is fuel related, but, that's as much as I can come up with. Does anyone know what the problem might be? I've already tried a fuel injector cleaner in the tank to no avail.

 

Have you checked for air leaks as suggested earlier?

 

My s type 3.0 had that problem and it was a air leak problem most likely that's what it might be

 

It sounds very much like a vacum leak. Check all intake parts, then start working with vacum lines. I got 5 virtual bucks on it.

 

Another possibility is changing the wrong coil - easily done if you don't make sure you know how they're numbered (grab the veh. spec file from FAQs).

 

I got the info on how the coils are numbered so that's not it. My mechanic did check for vacuum leaks but couldn't detect any. However, he did it the old fashioned way with soapy water and just listening so I guess that could still be the problem. I am starting to think I am going to have to fork over a wad of cash and take it to Jaguar to at least identify this problem. It's driving me crazy. Thanks!

 

i have a 2000 s type V6 3.0
my car had the same problem. it was a little hose called a breather hose. it had a big hole on the side of it. u couldnt really see it. only if u bend the top half back u could notice the tear. its located way in back of the engine on near top of the driver's side vavle cover.
it connects a hose to the throttle. it only cost me $3.95 at autopartswarehouse.com

 

Thanks! I'll have my mechanic check it out! Wouldn't that be great if it was that easy to fiX!!!