Ok, I'm still having a transient issue with my XK. Every once in awhile, usually after the car has been sitting cold for at least over night, the car will slow down and then speed up on and off, especially at highway speeds. This happens when my foot is absolutely stationary on the gas pedal, so it's not me. It happens whether the tranny is in sport mode or regular mode.

When the car speeds up, it flashes the "Poor Vehicle Performance" light on the dash for a split second, yet it's not screwing up badly enough to store an error code because every time I have a mechanic check for one, there isn't any.

The car acts as if it is spordically losing it's ability to sense what speed it's at and that results in the slowing down/speeding up bit. It's so intermittent that it's one of those things you could spend a fortune on trying to diagnose without every finding out what's wrong.

The car usually stops doing this after it's been run for the first time each day. Subsequent trips before days end usually result in everything operating normally.

Anybody want to hazard a guess as to what the hell is going on here?

 

How's your idle? Is your tach bogging up and down at idle?

My only other guess is something to do w/tb linkage. If the vehicle is speeding and decelerating at highways, this may be the culrpit. Then again, I'm not familiar if the Jag has a spring-mechanism or if it is electronic. I'm guess though if it were electronic and this were the culprit, it'd throw a check engine light.

 

I would guess at some sort of vaccuum leak. Sounds like once things heat up and expand it seals. But that's just a guess.

 

Close. Try only ONE out of THREE air filter cover latches actually engaged.

Must have really screwed with the air flow sensor because now it runs better than ever.

I don't know what Moron unintentionally or intentionally left those clamps undone but I have a good idea!

Let's just say he won't be seeing my money ever again![:@]

 

Nice good find, I was going to suggest that, the MAF or the TPS sensor of these cars have one might be the cause to an erratic idle.