My 2001 xj8 has started rumbling sometimes from the back when I first turn it on, and the rpms drop to 500. The rpm fluctuates slightly and then settles out while it is idling roughly. This seems to occur after the car has been driven for a while, and then started after sitting a short time. Also, seems to occur more when gas tank is half full. Within the last 6 months we replaced the left knock sensor, alternator, and thermostat. Check engine light finally came on, codes read misfire of some of the cylinders.

Any thoughts?

 

Wrong forum. Try the X308 forum.

 

Hi Lisa,

I have moved your post from the forum for the X350 to the forum for the X308, which is the Jaguar factory project code for your 2001 XJ8. Here you will find knowledgeable owners of similar cars.

It would be very helpful if you could post the exact codes that were scanned (for example, P0300, P0306, etc.). It would also be helpful if your mechanic could scan the fuel trims and post them here (Long Term Fuel Trims or LTFT, and Short Term Fuel Trims or STFT).

Also, I'm confused by your opening statement: "My 2001 xj8 has started rumbling sometimes from the back when I first turn it on, and the rpms drop to 500." What do you mean that it is rumbling sometimes from the back? Do you mean the rumbling noise is coming from the rear of the car?

Cheers,

Don

 

I suspect she is feeling the engine miss. I recall when I first got into these cars that the motor isolation is so much greater than typical vehicles that misses sounded/felt different and could be interpreted as a rumbling.

Agree the codes would be helpful.

-Mike

 

The rumbling is totally normal - they all rumble from behind the back seat, you can hear the fuel pump inside the cabin.

Your other issues are not normal

 

I don't hear my pump in the cabin, at all ...
On the problem, first thought reading the symptoms is a slowly dying fuel pump, or something else prevent enough fuel going around.
Should surely have a further look at it, not good.

 

Mine has been doing it for years and this seemed to be the consensus of the forum so I've ignored it. Once in a while it seems to idle a little rough for a few seconds while it rumbles, but it smooths out always before I'm ready to shift into gear and go. My guess is it may have something to do with the vapor recovery system.

 

Sound definitely varies based on how much fuel you have in the tank, so your fill up habits may be different than mine - I tend to run it down 2-3 gallons close to the reserve frequently (gauge saying under 30 miles remaining while getting 12 mpg)

Its also more audible in an enclosed car park than outside, and is usually (but not always) only heard after a cold start.

 

Thank you for all the answers- ok on the codes they were : P0300 P0301, P0302 P0303 P0305 P0306 P1316

yes, the rumbling is coming from the back of the car somewhere behind the seats and is loud. The fuel pump was replaced two years ago, I believe. But the idle is really, really rough and it seems as though it could stall, and I have never seen it do this on a full tank. But it finally gave codes, although the codes don't seem to help much.