To start, sorry for the duplicate posts. Trying to rewrite to deal with separate issues in separate posts.

Just this week I started having issues with it stalling (almost stalling) when hot at idle+brake (like braking hard for a stop sign, at which point it seems to not slow down much until the torque converter starts to disengage, at which point it dips below 500 RPM like it's stalling unless I let up on the brake slightly.) It actually has stalled out several times when parking, and nearly stalled a bunch of times at stoplights and stop signs. If I let up on the brake slightly I can compensate, but when I was trying to do that while parking this morning I got a horrid grind from the trans.

It seems to idle okay (maybe not fantastically) when in park, or when in gear, just not when shifting to reverse (pulling out from park) or when shifting to neutral (involuntarily, when braking)...it'll pause, dip down to or below 500 RPM, then surge slightly if I'm off the brake, and be back to ~650 for idle. Happens worst at the end of a drive.

And I did a battery cable reset this morning before my 35-mile mixed-traffic commute, and it's still acting this way.

Potential issues/debugging steps taken:

- I haven't caught a specific code yet from this, but my own OBDII reader is on the fritz (new one coming in the mail tonight). (CEL is on most of the time due to the purge valve issue.) Any specific live issues I can look out before beyond error codes?

- I know the throttle body needs cleaning, hoping to tackle that after I get home tonight.

- I happen to know that I have cracks/potential bad seals on both breather hoses, so they're due for replacement. Not sure if they could be affecting it that badly, though--I wrapped the joins in tape last night and it seemed to run slightly rougher of all things, but have slightly less of a problem braking at lights.

- Fuel filter was changed in the last couple years (before my ownership).

- Purge valve has issues, hoping to replace it soon, if I can figure out what part to order (got a separate thread for that).

- The last time I had a car doing something like this, it was a vacuum leak. If there was a vacuum leak (say, at the purge valve), anyone know the correct vacuum value for this car? I have a vacuum gauge available for testing.

- For a while when cold it seemed to have a really hard time catching, either not catching at all on the first ~5 second crank, or catching at an extremely low RPM and then coughing until it surged up to 500ish RPM. So I started (when cold) turning the key to prime the fuel pump, letting it run, then repeating (up to twice more) before cranking. That seemed to almost fix the cranking issue (I also replaced the battery and topped off the oil while doing this). I suspect the fuel pump is either slow or possibly dying...the one time I've had a gauge on the rail, it only read ~25psi after a 2second pump run. I suspect it'd read higher if I let the pump run its course (like I normally do now in operation), but I haven't had a chance to check. Another thing for tonight.

- Miscellaneous: I also overfilled the gas tank last week, I think :/ but that was after the first time it stalled in reverse (albeit not the later stop-sign issues). And it's overdue for an oil change, ah well. I have a spare coil handy and plugs, but don't think I'm getting misfire issues, I know what that feels like.

Anyone have any ideas about what I'm debugging here? I don't want to start throwing parts at things without reason, but I'm a little out of my depth with these systems. I'm rather scared of it being the torque convertor or lock-up solenoid...any way I could confirm or rule out issues with those?

Thanks so much for the help!

 

Updates:

Got my bluetooth reader in, and checked the codes...nothing logged since this morning, but the car was running low and growly and felt like reduced power since the battery reset.

LT fuel trims were low but positive: 2.3% for Bank 1, and 1.5% for Bank 2. And they seemed to drop somewhat at higher revs. Maybe a small vacuum leak somewhere?

Throttle position was about 2.5% at idle in park. Not sure what normal is for this car.

I've ordered a new purge valve, it should be in in a week...

 

Tiny trims are OK.

Did it do its bad act as you watched them though? (Suppose it's a hose that flexes causing a leak, but didn't as you watched, then you'd not know.)

 

@JagV8, after cleaning the throttle body and resetting this morning, they're a bit higher but consistent at ~3.5% each. Leastwise they were when I checked at the end of my commute. As far as watching it, the issue is only transient, when the transmission is shifting or unlocking when the car is hot and in operation...so I have no other observations other than no P codes returned with whatever it's doing.

Update: cleaned the TB this morning, reseated the intake there and at the MAF sensor. Still really slow trans torque converter release at a stop, causing a huge dip in RPMs and a slight surge after, but gaining confidence as the idle seems stronger and it recovers well. Driveable now without a lot of worry. Unfortunately the issue starts sounding like a trans issue. Really hoping not to have to open up the transmission...

 

So does it only do it when you are moving and braking or can you just park up and apply the brake and stall it? If this is the case you may have a ruptured diaphragm in the brake servo unit that is opening up when flexed as you apply the brake. Try clamping the vacuum feed to the servo and then apply the brakes to see if the problem goes away.

 

Have you tried cleaning the MAF? Do not use carb cleaner as some of the MAF's have a coating that carb cleaner removes.

Dead easy to remove the MAF and clean. Remember to clean the actual MAF Sensor though and not just the temp sensor. Even if this is not your actual problem it will certainly improve the running of your car anyway.

 

Here you go. Take a look at this :-

http://www.jaguarforum.com/showthrea...75123&page=224 #2236

and

Franks XKR Story. - Page 225 #2245