Over last three months XJs (6 cyl) has started to hesitate and stall - seems to be getting worse. Took car in twice to local repair who looked at a number of issues, but were not able to resolve the issue. No issue restarting the car. Their summary follows. Car is unsafe to drive, I love the beast and an desperate to get it fixed. Suggestions please.
Lee

vehicle Time In: 5/6/2022
1995 Jaguar XJS black
Odometer In: 80779 Odometer Out: 80844 License: EX525MI VIN: SAJNX2741SC199665

Second Exam

Installed fuel pressure gauge, spark tester to try to narrow down if a spark , injector pulse or fuel problem
Noticed cracked intake boot. Repaired the boot because a new one is not available.
could not pinpoint direction?
fuel pressure -OK
never lost spark
injector pulse looked OK
cleaned and reset throttle plate- did not help

Installed scan tool to monitor pids while driving, all readings looked OK.
When concerns happen scan tool data resets and acts like lost power to everything when car acted up.
Monitored power, signal and ground at TP sensor- never dropped out?
Felt like tip in hesitation, possible throttle position sensor = installed sensor for test purposes – did not fix concern.

Vehicle Time Out 4/5/2022 3:44:16PM

First Exam

Checked fault memory and there were no faults found. Cleaned throttle body and found intake boot not sealing properly on the MAF. Re,installed boot properly and test drove about 20 miles and the vehicle never acted up.
Noticed while driving that the vehicle takes a very long time to get to operating temperature. Possible thermostat sticking open. Also noticed the ABS light went on and off and set a C1095 Pump motor failure. Recommend Diagnosis if light comes back on.

 

Vacuum leaks can do this… I’m confused as to which intake boot is damaged? I had an intake manifold gasket leak. Would move the voltage needle every 32 seconds. If I had the car loaded up with AC, headlights, radio, it would stall me out at a red light. It was difficult for shops to find this failing gasket…took several tries, but once replaced, all was good.

First off, you may want to replace the crankshaft sensor. Shouldn't cost a lot, relatively easy to do and is a common problem. Once past that:

1. EGR Valve. I’ve had similar issues on my first 96 XJS, it eventually granted me a code, but it indeed was eventually. Went through several stalls until if finally decided to grant me the code. Once I replaced the EGR, problem went away.
   
2. TPS - can provide a bunch of mystery problems. Replacement is not cheap, but you might have to throw a part at this problem. The TPS tends to bench test well, but provide difficult to diagnose problems like this.
   
3. Coolant Temp Sensor. You mentioned that the car wasn’t getting to temp fast enough. The thermostat should definitely be changed, but there’s a $20 Coolant Temperature Sensor that you can replace in 5 minutes that can also prevent you from going open loop. If the coolant temp sensor is reporting something opposite, it could cause these problems. Recommend doing both regardless.
   
4. Oxygen sensors. When were they last changed? They don’t last forever. With 80k on the clock, they are past due. You have four of them. The downstream sensors do the heavy lifting, so if you’re gonna be cheap, those are the ones to do, but I would bite the bullet and replace them all.
   
5. IACV - Idle Air Control Valve. It is bolted in with two small 5.5mm bolts. They loctite them in, so if you don’t heat the bolts up before removing them, you’ll break them. These do fail, and I don’t believe they are expensive. Make sure you have the gasket for them, and there’s an o-ring that tends to be missing as well.
   
6. MAF Sensor. Could be failing you, but I doubt it. It doesn’t seem to be too common a problem, but I thought I’d add it to the list. Maybe a can of MAF Cleaner from the auto parts store and clean the sensor.
   
7. Failing coils. Not sure how to diagnose these, but they do tend to throw out a p030x code. At least a p0300 code, so I’m not convinced that’ll be a problem. If you pull them out and notice oil in any of the spark plug wells…it could be a sign. Running the engine at night would reveal sparking in the wells, which would also be a sign. Lastly any crack to the coil bodies, or rips in the plastic boots…yup…would be a sign.
   

 

I've had the same problem with my 96 several times. The first time I replaced the EGR and that cleared the problem. The second time it was the CPS. The car would run fine but would stall out when I took my foot off the gas and the engine returned to idle. In each of those situations, the engine would immediately start right back up. I now have a problem where in addition to stalling, the cars loses power and is quite scary. I've also noticed that I have a woosh when I open the gas cap and I'm not sure if it is from pressure forcing air out or vacuum sucking air in. I'm going to check the rochester valve and associated pipes and hoses to see if that corrects the problem. I think we just have to realize these cars are now over 25 years old and things are just wearing out. Hopefully parts will remain available.

 

Replace the Rochester valve asap. I waited and I think my tank imploded a bit.

it’s a $30 part and should take you no more than an hour to do. AC Delco makes a part, It’s a common part, so easy to find.

Tell me more about the losing power bit you’re currently experiencing, but probably best to open new thread