Engine Performance problem
1988 Jaguar XJS V12 Two Wheel Drive Automatic 39000 miles

I have a 1988 Jaguar Xjs convertable. Reciently during a trip 10 mile trip it started losing power and I almost didn't get back home. The last mile or so max speed uphill was 3 or 4 mph. I can get the engine to run but not enough power to move up the 10 degree slop of my driveway.

The fuel pump is opperating but I didn't check pressure. Lots of exhaust ( Cat Convert not clogged). Replaced the fuel filter.

Any suggestions?

Does it pop and spit or is it like there is no throttle response? Also, is it the same in neutral as it is in drive? Please advise.

No, it does not pop and spit. It takes a while to start but once started with the transmission in park and with the gas peddle depressed perhaps 1/2 way to the floor, the engine starts to accelerate and after about 3, 4 or 5 seconds the RPM's are high enough that I'm not comfortable with the high engine speed so I release the gas peddle. The engine doesn’t stall and I can repeat the above. If I start the engine then put the transmission in drive, there is not enough power to move the car and the engine stalls.

I don't know if the following is related but prior to this problem I experience the following issue. Upon startup I would place the trans in drive, depress the accelerator and the engine would not accelerate. I would quickly press then release the gas peddle 5 or 6 times then the engine would accelerate. I would have to repeat the process each time I wanted to accelerate away from a stop sign or red light until I had driven perhaps 1 mile. After that, the engine would perform normally.

I forgot to mention. The coil produces a good strong spark

Your last paragraph was very helpful. I have to believe, by what you have posted, the air flow meter is the culprit. This unit senses how much air the engine is calling for and tells the computer to adjust the fuel accordingly. if the AFM thinks you are still at an idle, no matter how much throttle you give the engine, it doesn't increase the fuel. A new AFM is big bucks. I have an '88 XJ6, but have never had your problem. When I have a high dollar problem with mine, I'm not afraid of used parts. Pricewise, it doesn't hurt quite so bad if it doesn't fully solve my problem. I use a company on the internet called URG autoparts. Here you can get a list of the salvage yards accross the US. that have the part you are looking for and for how much. Their web address is; "www.urgpartsearch.com/searchframe.cfm". At this site you can find almost anything you want for your car. Hope this helps.

Thanks for your reply. However, my Jag doesn't have an Air Flow Meter/Mass Flow Sensor.

Do you think it could be the the ECU (Engine Control Unit) Computer.

Your right. '88 XJ6 used a meter, XJS didn't. Your air/fuel mixture is controlled by the throttle position sensor. This could cause a the ECM to think you are not accelerating and thusly, not giving the engine any fuel. This unit is located on the throttle body with a microswitch that turns the cold start injectors on/off when needed. Do you have any VCM codes stored in memory? This also could be a clue.