My Jaguar XJS 4.0 L 1996 Americanmodel has a RPM problem.
The RPM goes up to 1600/1800 RPM. No matter if the engine is cold or warm. When I drive, he accelerates on his own.
My mecanic checked a lot of hings but the problem is still there.
I don't know what to do anymore.
Is there somebody who had the same problem?
Thanks.

 

You have an air leak into the inlet manifold, or round its edges. try completely blocking off the throttle inlet and see if it runs.

 

Hi Greg.
My mecanic already checked it. It must be something else...
Thanks for responding.

 

Hi Douggy-

mid your problem is high idle, then this problem is very common on the AJ16 engine - there are lots and lots of topics about it and we can probably help you diagnose fairly quickly. If the problem is that the car is quite literally acc elating on its own, then I can’t say I have heard of that one before, but it sounds related to the cruise control or TPS, right of the top of my head.

please clarify is the car is literally acc elating on its own or if this is a case of fast idle.

 

Hi Spikepga
The RPM is very irregular. When the engine is cold, one time the rpm goes up to 1800 and one time to 1000.It"s the same when the engine is warm. One time it goes up, one time it goes down. All this in N.
In D, when you accelerate a little, the car is accelerating on his own. So I have to use the brake more than to accelerate..
Is it the ECU Module ? My mecanic is out of ideas. And he knows this engine because he used to work on it when this car was new in an official Jaguar dealer..
Thanks

 

If your mechanic really has completely blocked off the throttle intake to the manifold, and the car still runs, there HAS to be an rogue air inlet happening. It is a matter of blocking off all possible air sources until it is found. An internal combustion engine cannot, repeat cannot, run without air. Ask him to go round the inlet manifold carefully looking. It could be a cracked manifold or a loose one, or a anything, but air is getting in!

 

I have the same problem. When inlet closes it falls out, so no air leak. All possible common problems already investigated. Including calibration TPS.

 

That doesn’t make sense.

1. I’m assuming you’ve tried a replacement TPS, even a used one. This is a very strange failure, and I suspect that the TPS could be installed 180 degrees in the wrong direction. The recalibration would not fix that large of a deviation. I’d see what happens if you rotate the TPS around.

2. I’m assuming your mechanic has checked that the throttle plate is closed at idle and there isn’t anything holding the throttle plate open. It’s been cleaned? These throttle bodies are notoriously sticky.

3. The MAF could be so bad that it sending false air readings?

4. I’d mention oxygen sensors, but those don’t get read until the engine is warm.

5. Lastly would be the ECU. If there isn’t anything wrong with the TPS and it’s installed correctly, and the throttle body butterfly is clean and closed, and there’s no large air gap at the intake manifold, and the MAF isn’t telling the ECU that it’s getting tons of air, then I believe the MAF could be the culprit.

 

Agree with checking the throttle plate. Just remove the air intake boots in front of the TB and take a look inside to see the throttle plate. Is it completely closed? Is the throttle cable adjusted incorrectly so it's maybe pulling the throttle open slightly? There was a Service Bulletin on the throttle return spring being too weak. Removing the throttle cable, can you easily move the throttle by hand and have it return to home without binding? These are all easily checked

 

Hi Greg,
I told my mecanic to check this. When he will do it, I don't know because Ilive in Spain... Things need more time here...
But I let you know when he did.
Thanks

 

Hello everybody,
My mecanic checked everything you said. It's not this.
He says it's the ECU module number LHE 1410 ED.
My question now :
Is there anybody who knows where I can find one?
Please note it's an American ECU module I'm looking for because my car is American.. A European does not work on my car.
Thanks.
Dirk.

 

has he removed the ECU? Does it have water ingress? The only reason these ECU’s fail is due to water ingress issues.....if in fact the pins are corroded, then you will need to find a ECU, but your description of the failure mode does not coincide with my own ECU failure mode or others.....my car was sputtering and backfiring and would suddenly “fix” itself.

 

Can also be false air for the air mass meter, for example hose of air pump loose or torn. Then you have a wrong airflow in the suction tube and the sensor measures wrong values. That was the problem with my XJS.

 

I have a 1996 USA ECU from a 1996 car that was running great. It hit a pole at hgh speed and was totaled. $1000+ shipping.
I know its good becasue the car was still driveable and I moved it around during the disassembly process.

 

Just for clarity...

1. The throttle plate is clean. Easy enough to check. Pull off the intake hose and stick your fingers in there.
2. The TPS has been reset? You need a diagnostic machine equipped with Jaguar specific software to do this. It can be done manually, but there's a process...
3. The harness connection to the TPS is good? My 1996 is starting to get finicky. The wires are old and I believe are not making a good connection anymore. That can be part of your problem as well...

 

Hi icsamerica,
Can you send me a picture of the ECU with the order numbers on it ?
My WhatsApp is 0034 644 76 19 24
Thanks

 

Hi Vee
I will tell my mecanic.
What's a TPS ?
Thanks a lot
DOUGGY

 

Throttle Potentiometer Sensor.

It tells the car what the position of the throttle body is.

This engine is notorious for gummed up throttle body butterfly plates and strange effects from old TPS. They bench test fine, but in reality cause tons of mystery problems.

When the throttle body and the TPS lose sync, the TPS needs to be reset so that it knows when the throttle butterfly is closed. If not, the engine will race because even though the throttle is closed, the sensor thinks it’s open, calling for gas and speed.

Other times the butterfly is simply caked with old oil exhausted from the camcover. It cakes on the spindle and/or the throttle body walls and prevents the throttle plate from closing. So even though the foot is off the gas, the plate is still open and the engine is calling for gas and speed.

 

I dont use whattsapp but here is a pcture of the ECU.

 

Not trying to dissuade you from purchasing this ECU, however, if you purchase this ECU, you will still have to reset the TPS using Jag specific software. Make sure your mechanic can perform this service, or you will not be able to resolve your issue.