Hello all.

MY 96 VDP developed a habit of intermittently stalling when the I lifted quickly on the accelerator or intermittently at idle. THe RPM's drop to 500 and the engine dies out. The throttle body was cleaned not long ago (3000 miles) so I don't think a dirty TB is the problem.

At this point now the car won't idle unless I un-plug the MAF sensor. When I disconnect the MAF sensor the idle smooths out and no more stalling but it misses (coughs) when accelerating from idle only. So the gas has to be feathered to get off the line. Once rolling, the car runs smooth, again without the MAF sensor plugged in.

I can plug in the MAF sensor back in when running and the car will run fine for several more starts but soon the rough idle returns upon start up and the car will stall unless you keep the revs up. Disconnect the MAF sensor and wow, the idle smooth out again....

I tried a spare MAF sensor with the same results.

I cleaned both MAF sensors as well.

Any clue what the problem could be?

Thanks

 

btw, I'm now driving it with the MAF unplugged because that's the only way the car will reliably run even with the cough off the line...Is this bad for the car?

 

If I remember correctly the input power to the MAF is electrically tied into other devices that may be sucking down the MAF resulting output signal straight wired to the ECU . As A cheap try you would unplug the other devices . Codes ?

EVAP valve located under air filter with 2 fuel vapor lines attached running along the body frame rail .



How is that V12 doing on your other ?

 

Or is it simply just worn wires or poor connection resulting in inaccurate data being supplied to the ECU?

 

Thanks for the replies. I did find some frayed wires going into the throttle position sensor under the Throttle body. When the wires were wiggled, the idle would jump around. I cleaned up the wires and spliced the bad spots.

With all sensors reconnected, I now have a pretty rough, or almost cycling, idle. Again when MAF sensor is disconnected the idle smooths out. When TPS is disconnected, the idle ramps up. All other sensors along intake including EVAP don't affect idle.

Still searching for smooth idle. Car occasionally almost dies at idle, or when coming to a stop, but catches it self with the cycling.

 

How is that V12 doing on your other ?[/QUOTE]

The spare fan assembly solved the problem. Haven't had a chance to see it eh one bad fan motor is serviceable in the original assembly. I'm still dealing with secondary air injection system fault.

 

On the V12 X300 fan looking at your original parts , I just hooked mine up to a battery charger

The X300 does not have a overheat light and I would suggest rerunning that jumpering of the 3 wire temp switch connector test . This does not test the switch .

The V12 with your miles would be a great lose if it were to overheat . As an insurance policy you might think about replacing the switch before the old one fails open and you don't catch it . Up to you .

Back to the AJ16 engine as one sensor drops out of veiw as in removing the connector the ECU by design reverts to a different map which in your case may be biasing up on the good side a under responding ( or binding ) set of fuel injectors most critical at idle . Have you tried a tank mix of injector cleaner before removing injectors for a more thorough cleaning ? Can you read fuel pump pressure at the rail of 43 PSI ( after the regulator output as they go bad $ 65 ) at idle or changed the fuel filter or swapped out the fuel pump relay (not carrying the needed current ) ?

 

The XJ12 electric fan assembly from ebay runs (both fans) on low speed when temp gets hot enough. When the AC is on and ambient temps are hot, fans run on high speed. When car is turned off, fans run at whatever speed they were running at for a few minutes.

So cooling fans seem to be operating correctly now. Are you suggesting I change out radiator temp switch as a precaution? I does seem that if that switch completely fails the electric fans won't run at all. Or are you suggesting I wire fans so they run with the key, in which case maybe I wouldn't get high speed from them?

 

There are 3 relays inside the fan control relay module and they should be either on or off as designed . I cut mine open to find out if I could repair them finding it full of water . In toying with it I could get full or less then full speed on the fans . I will be sourcing a replacement fan control relay module . X308 part is a substitution .

On the AJ16 a free and easy try would be to cleanup the Papa Indy 1 and 61 connector that gets corroded containing the injector and coil power source wire for each and is common to your V12 as the secondary air pump wire runs through it .

 

OP,

Did the problem start when you cleaned out the TB? or it did happen before TB cleaning?

 

Problem popped up a couple thousand miles after cleaning TB. The car is pretty much un-driveable now. Low, rough idle causes stalls at every stop now...

 

Have you ruled out the possibility of a bad crankshaft sensor, a failing TPS, fuel pump relay, fuel pressure regulator..?

 

No I have not. If I change the TPS will I need to have a calibration done to it?

 

Well I had a very similar problem. Please check my thread. I hope one of the many things I tried to fix this problem works for you. Car doesn't stall anymore from start up or at stops. I had to resort to a local mechanic. They performed fuel pressure, plugs, cleaned out throttle body again, and then adjusted the TB as well. Once I got my car back it worked but cost me $300. No more problems though.

https://www.jaguarforums.com/forum/x...tartup-186412/

 

In my opinion as long as you keep the TPS reading the same as the one you are are replacing you shouldn't have to do a ECU orientation . The value at idle stop should be 0.60 + or - 0.02 volts and originally oriented to that . If you install a new one and the value is different from the previous the TPS the ECU may not read it correctly and you would have to tweek to ECU to do so . Mine was at 0.63 volts out of range and had to oversize drill open the mounting holes to be able to twist and put it on 0.60 . No telling If it was oriented to that 0.63 or not but I doubt it . Pipes are off now and not able to see on mine if twisting the TPS to be in range at least made a difference . You can read this value with the key on and engine off by tapping into the return (Green / Yellow wire ) to the ECU wire as it goes over the top of the engine . You can twist the throttle shaft and watch the voltage change . I personally wouldn't change the TPS or adjust it unless I had proof that it was bad . Clean connector on the bottom and ensure that it is locked into place . Mine had the locking bar doinked off by the previous owner and the connector would migrate off losing connection .

Someone replaced the plugs to a three prong E3 .48 and resolved his idle issue but I think this positively compensated for something else in the engines regulation or foundation that was below par .

You can use this same process of compensating for a weak coil by bringing the plug gap back down to 0.035 as the Champion RS12YC is the recommended plug from Jaguar as this engine is apparently sensitive to incorrect plugs or exotics .

The quality ( not timing ) of the spark and clean injectors are examples of the foundation of what your engine needs other the sensor controlled regulation that may not have a problem .

 

Instead of wild guessing, in which case the most common culprits for stalling are the crankshaft sensor and the coils, does the car throw any codes? It is about time to do some systematic investigation.

 

By asking questions on components or sensors other then none opens up discussion that may lead to a solution as you and others think through the system , so in a way it is good . The more input the better . This is the Mastery Approach . Not saying I am there but I have learned alot from others inputs .

 

Thanks for all the great input for my issue. I did have a little time to day, finely, to get the VDP in the garage. It did have some new codes:

P0727: Engine Speed Input Circuit No Signal
P1316: Unknown code - More information may be available on the web
P1775: [Mitsubishi] 2nd solenoid
[Seat/Audi/Volkswagen] Hydraulic Pressure Sensor 1 adaptation at limit

I only had time to swap coils today. Swapped with 6 good Lucas coils and no change in car...

Tomorrow, I'll try a few more things...

 

https://www.jaguarforums.com/forum/x...t-codes-31688/

 

Parker's DTC reference table is very useful. If a new CPS and a set of new coils (there has been a long discussion on various horror stories on new coils unless they are made in Japan) cannot fix your stalling problem, it could be very much the fuel and fuel injectors, like water in fuel tank, fuel rails and injectors, causing internal rust and combustion problems like misfiring and stalling. However, I would try testing the fuel pressure regulator first, then fill the tank with a bottle or two of injector cleaner, and see if there is any improvement, before emptying the tank and clearing up your fuel pipes, fuel rails and injectors. The spark plugs may also need replacing if they have been working with watery fuel for some time. Hope it is just the fuel pressure regulator.