Having an issue with my XJS "off the line", right before the 1-2 shift sometimes it feels like it doesn't want to move, almost like trans slippage. I can equate it to driving a car with a high stall torque converter, if anyone here is familiar with that. Also it stumbles and bucks around when you get in the throttle at those lower (1000 or so) RPMs. Often you can "power through" it, i.e., keep in the throttle and get it to launch. Also once at startup idle the tach was going all over, from 500-1100 RPMs. Nothing noticeable at higher gears/RPMs. Anyone have any suggestions on the cause? I doubt it was just "bad gas"... I'm thinking clogged fuel filter, fouled plugs, sticking throttle blade?

 

Well I installed a set of cold air intakes and I was was getting some "popping" under throttle at those same conditions. I cleaned and lubed the throttle blades, and today I replaced the fuel filter. Ran good except for one incident, entering the highway from a ramp, it "stuttered" and I saw the tach bounce around under 1500 RPMs again. I might replace the O2 sensors before I inspect and change all the plugs, just because it's easier. Any other ideas?

 

For this and your other problems I would start with:

Check for vacuum leaks. Lots of hoses and fittings on a V12 so take your time
Check the bushings at the throttle linkage at near the rear of each cylinder head
Set throttle blades at .002" and synchronize the linkage
Check TPS function with a volt meter
Block off Aux Air Valve and see if anything changes
Check advance mechanism in distributor...they often seize tight, and the vacuum advance canister is often dead

Post back if you need details

Cheers
DD

 

I looked through the owner's manual and Haynes guide for clues, and discovered that I have an O2 sensor warning light! I've verified that the bulb works, and the light is not illuminated, so I'm going to move onto plugs and wires at this point. I had also considered TPS, throttle potentiometer, or the advance mechanism.

 

The Oxy Snesor warning light was strictly mileage triggered (every 30k miles, I think) and had nothing to do with actual sensor operation/performance.


Cheers
DD