This may be related to my high idle problem as well.

When driving down hills, if I take my foot off the gas, the engine will continue revving up as if I still have my foot off the gas pedal. The engine is warmed up, the cruise is definitely off, and pulling up on the accelerator pedal has no effect.

I had it hooked up to a computer. The OBDII computer was reading the throttle position at a steady 16, apparently the minimum opening percentage, as I never got below that number. So I don't think the throttle is getting stuck. (Throttle body was just cleaned yesterday)

The MAF air flow rate seemed to increase with speed, not the reverse.
Could this be caused by a faulty temp sensor? The OBDII also read the engine coolant temp at a steady 185F.

Could this be caused by a faulty stepper motor? (also being the culprit for the high idle at 1200rpm)

Thanks

 

From your posts it sounds like you got the BRG 96 you where talking about-great!! Maybe a picture or two?

On *any* AJ16 car that has not had the Coolant Temperature Sensor ,Crank Position Sensor changed I would definately get those done along with checking the ECU pins and protecting them with a synthetic against water and checking the main grounds..... not that i think they are related to your throttle problem, just saying. Plus if you where driving hard and the OBD2 scanner keeps on telling you 185...,that's pretty much confirmation for a bad or soon to be bad CTS

I have to say I have heard of many TPS failure modes on AJ16's, and that's not one I am familiar with. The high idle could be the ISCV, but the fact the car thinks that it's going faster than what it thinks its going makes me put my money on the speed sensor modulator, the white shielded wire that runs from it to the sensor in the differential or the sensor itself.

There was a guy on JL whose AJ16 was doing the high idle and after lots of parts he realized the car thought it was moving when it really wasn't , he untangled the white wire from the speed sensor modulator to the differential, wrapped the speed sensor differential in foil and grounded it and problem solved.

Even if you end up needing the SSM, it's less than 60 dollars from Jaguarclassicparts.com, the TPS and ISCV are also much cheaper thru them than if you where to get them here.

Good luck

 

As soon as I get this sorted out, I will post some pics.

In the meanwhile, I may have resolved my high idle issue. I tried another manual idle base reset and I couldn't get the car to keep running. It would turn over and die. After about the fifth time, it stayed on and the idle remained at 800. It seems to be fluctuating in the 800-860 range, but I think it may just be doing that to relearn itself.

The issue with the RPM rising as I'm going downhill is still happening. Its the strangest thing! I was going downhill, I popped into neutral and the RPMs started climbing through 2,000 RPM! The throttle position was at 16, the engine load was at 15%, but the beast wanted to go higher! When I brake, it does slow the RPMs down too.

It seems that the engine somehow wants to match what the wheels are doing? Does that even make sense?!?

 

Got the car back and the engine is SUPERsmooth.

I wish the transmission was smoother, but you can't have everything.

The PDU hookup resolved the idle and the engine revving. ($100)

I also had the rack and pinion seal replaced. ($400)

My oil sending unit was replaced too. ($160)

I still have to replace the camcover gasket. That should be here in a day or two.