So I've had this problem ever since I got my 93 xjs 4.0 running. Basically it starts and runs great, but when I drive then come up to an intersection, or slow way down then let off the gas, the rpm drops and I get a shudder and "brrrr" sound for a second then it picks up and is usually fine, however if it's stop and go traffic it does it almost every pull forward and stop. Over time I've cleaned the throttle body, maf sensor, replaced the air intake valve and tried numerous adjustments to it (it's almost completely closed now) and have of course run injector cleaner and seafoam through it numerous times. New plugs wires, cap, rotor, coil, and fuel filter. I'm sure there have been other things, and sometimes I think it makes a slight difference, but then the next time I drive it does it again. Anyone else have a similar thing? It ha stalled once or twice, but that's usually when it's cold and I just start it and then back up and go to put it in drive, then on a rare occasion it'll stall. Maybe twice in the last year type deal.

 

Hmm, I don't know, but it sounds like its having trouble downshifting. Slowing down and staying in high gear could cause the engine to shudder if it gets bellow idle speed. Have you serviced the transmission at all?

 

May need to get the TPS reset.

I would also look at the IACV. When was the last time you replaced the oxygen sensors?

 

No I haven't. I keep telling myself I really need to do a filter and flush.

 

Not sure how to reset the tps really. I did replace the iacv and that's what I have almost screwed all the way in. I tried the "setting procedure" that I found online, but I don't think it made any difference. I'll say I haven't changed the oxygen sensors.

 

For the 96, you would need a Jaguar specific device to reset it. I have to admit, I just realized you have the AJ6, so disregard my TPS advice. I’m not familiar with that part, so I’m not sure how to diagnose a failing TPS. I know if the TPS and transmission are not in agreement, you could be seeing your issues.

Id take a flier on the oxygen sensors. If they haven’t been changed in 40,000 miles, I’d say they were due anyways. Could fix your problem. Certainly would make sense. If the oxygen sensors are getting lazy, they could be telling the engine to over/under fuel the engine.

 

I'd almost bet the sensors are factory, so about 90k miles on them! Lol! I'll look at replacing them! Definitely wouldn't hurt

 

No, definitely will not hurt, and very likely to help.

When the car is idling, in drive, say, at a light, do you notice any fluctuating on your tachometer? I had an issue where I would see a drop in RPMs every 32 seconds. In the wintertime, or on a nice day, not a big deal. But during the summers, when the AC was running, the radio on, maybe the headlights on as well, that RPM drop would sometimes stall me out at red lights! It ended up being a bad intake manifold gasket which was allowing unmetered air into the engine. Two shops could not find that issue, a third finally did, and the problem was forever solved. Another thing to consider.

 

No its usually steady as a rock when just sitting in idle. It might not hurt for me to spray around the intake manifold and see if the rpm jumps anywhere. Worth a try too

 

Let me know when you are able to replace the oxygen sensors and then the IACV. Oxygen sensors are a regular wear part, so it wouldn't surprise me if they have begun their death spiral.

The IACV is a common issue that eventually goes bad. Be careful, the tiny bolts that hold it in place will snap.

 

I actually have replaced the iacv. I've even pulled it a couple of times to make sure it didn't clog or get sticky or whatever.

 

All that is left are the oxygen sensors then...

 

I have one ordered so we'll see when it gets here 😊

 

One? I believe you have at least two, don't you? (The AJ16 uses four!)

 

I am not sure, but I believe that your car has a torque convertor lock. If it sticks, you get this result.

 

I would have thought so too, but all I was seeing when searching the forums was one, and when searching parts all I saw was one listed as upstream. I guess we'll see when I actually crawl under it to look

 

I'm pretty certain it does have the converter lockup. I know I've read about the little stutter around 55mph being from that, and I have that too