I've had an XJ8 for about a week now.. and I've hit my first issue that's got me stumped.. so I figured I'd harass the forum for ideas. Every other issue I've had has been resolved with a quick search of the forum (and new belts!).. so fingers crossed!

Mine's a 98 XJ8 with 130k on it. I know virtually nothing of its history, but when I bought it it had been sitting for a while and was flooded. Once I'd cleared it out (throttle to the floor, crank 'till it fires), it's actually been fine.

The problem is.. when it's warm, it stalls when you first put it in gear. In other words, the sequence goes.. foot on brake, turn key, engine fires, shift into reverse, revs drop to ~500, and half a second later the car stalls. If you're *really* quick about taking your foot off the brake, it's OK.

It also seems to have no engine braking to speak of - at speed, if you take your foot off, it barely slows down at all.

I found a bunch of references to a TSB to replace the throttle body - mine was full of black gunk, but I've no idea if it had ever had this work done. I know the TSB is expired now, but is the replacement throttle body any different?

So far.. I've cleaned the throttle body and both the breathers (the part-load breather wasn't actually blocked!), and replaced the main belt and tensioners. No idea if the timing chain tensioners have ever been replaced.. but that's next on my list to check.

Any and all advice much appreciated

 

Close, no cigar. Try cleaning the MAFS. Are you setting any codes?

 

No codes. It had a misfire code when I got it, but that hasn't come back since I unflooded it.

 

Oh, and it has a truly monstrous cone air filter where the normal filter box should be. It says 'Spectre' on it, and it looks amazingly tacky. I did wonder if this was related.. and aside from looking bad, I didn't think to replace it just yet

 

An improperly oiled, or even an properly oiled aftermarket filter will fowl the MAFS. Never found a reason to replace the original Jaguar filter. The cone heads advertise more air but at the cost of filtered particle size plus an oiled air flow.

 

This is something my XJ8 does as well (otherwise it is running great).
I have to admit that this special problem only occurs since I was messing around with the TPS.
Even my (independent) Jag mechanic was not able to fix that problem.
I had the Jag in the shop to adjust the TPS and got it back with the words "everything is set up quite right no need to adjust the TPS".

I'm not very happy with that "solution" but haven't found another way to solve that problem so far (Jag dealers are about 50 Miles away).

David

 

The stall may be linked to a faulty throttle body - have you tried disconnecting the battery touch the neg cable to the pos post. The engine management is then back to factory settings. After you clean the mafs/throttle body, this is something that you should do, as the engine management will re-calibrate the throttle position and throttle butterfly. Initial start-up the engine revs climb to around 2000 rpm for maybe 5 seconds, then gradually fall back as the ecu does its thing, it should settle to a normal idle tick over.

 

Thanks for the replies, all - useful stuff. I had no idea about the 'factory settings' reset tip - although that does make perfect sense. I cleaned the MAF last night, and no stalling this morning.. but I haven't tried a "hot start" yet.

I actually have a spare MAF sensor and filter box in the trunk this morning. If it misbehaves, I'll swap them out.

The "run-on" behaviour actually feels to me like a sticking throttle cable.. but my background is in much older cars - '70s Jags and Triumphs, where everything was cable-actuated and there wasn't an ECU in sight. Maybe I'll look at the throttle position sensor also; at the moment, I have a "spare" XJ8 to pull parts from to test, so I intend to use it to its fullest.

 

A sticking throttle cable would be easy to detect.
Remove the black plastic cover under the bonnet and you can see the throttle cable arrangement.
Check if the round black plastic drum (sorry for my loss of correct wording) on the left side of the throttle body is in fully closed position.
After that have someone step on the pedal and releasing it very gently. Now you have to observe the cable "drum" attached to the throttle body.
Will it set to idle or not?

There is also a threaded square black plastic "nut" around the end of the outer throttle cable. It is secured with a zip tie (!). On this plastic "nut" you are able to adjust the slack out of the cable. Maybe a former owner took too much slack out of it?

After checking the throttle cable I would go for the "reboot" to get back to the factory settings and calibrate the TPS.
This is in fact what I will do on the weekend to try to solve my throttle problem.

David