Tonight I cleaned my MAF senor and thottle body, afterward I disconnected the batterys negitive cable for 10 seconds. I reconnected and started the car.

Instantly I noticed I high idle around 2000rpm, then after a short time the engine started revving on its own between 1-2500rpm.
I put it in gear a drove a short distance and the car was pulling away from me.

I then turn it off and back on and everything was normal.

What just happened?

 

At a guess I'd suspect it was just the ECU initialising & adapting to the electronic throttle again, as any previous data & characteristics will have probably been lost when the battery was disconnected...

 

Perhaps I shouldnt have turned it off when it was doing it then?
I may have to reset again?

 

U need to unplug battery negative at least an hour so all the modules and computer drains of power. Then reconnect. It should not do what u described. Any check engine light? Clear and erase codes before doing all this.

 

No check engine lights....

 

Why?

I was under impression that if you disconnect BOTH sides of the battery, and then cross them, all the modules and everything, clears instantly.

 

. . . and the ECU will run a high idle until it recalibrates itself through a 'drive cycle'. No big deal, just drive it for a couple days and the everyone will be happy again.

Drive Cycle - https://www.jaguarforums.com/forum/x...asy-way-50358/

 

almost a hard reset........search threads to find interesting words on this

 

Do NOT cross battery cables!!!

 

That would mean every Jaguar tech who has ever described a hard reset on this and every other Jaguar board has been wrong then. Multiple times. Highly unlikely.

As long as the battery is out of circuit by disconnecting at least one of the battery terminals, all is well.

 

The high idle should go away right after the hunt phase at first key on after a reset. If you reset, then turn the key to position 2 without starting, you can hear the throttle plate calibrating. Once started, it may hunt up to 1500 rpm, drop to below normal idle one or more times, then settle at the appropriate idle for the current engine temperature and lower to normal idle as the engine reaches operating temperature. It should not take several drives.

 

There is a training procedure - https://www.jaguarforums.com/forum/x...connect-74146/
I'd guess it is applicable to your car.

 

Ok perhaps I should re-set again then as I turned it off half way through its set-up?

 

Yup. At least one of the terminals, but I take them both off (and away from the battery), and cross them for few seconds. It instantly empties all capacitors, and everything goes blank. I am not a technician, but I read,...a lot.

 

Plum is correct. Throttle body over time collects carbon buildup around throttle blade which is normal. Cleaning the the throttle body removes buildup so the ECM will relearn throttle blade location to properly idle. After disconnecting battery the car will also run funny for 1 key cycle which is normal. With both battery cables disconnected from battery connect pos cable to neg cable for 10secs and that will removed charge from all modules.

 

Ok I misunderstood what he was saying plums and Daniel. I read and thought he was disconnecting and crossing terminals on the battery. Sorry. I've done the hard reset before.

 

First read thru, I got the same - no need to get jumped on for caution. There's more ways to skin a cat I've always just whipped the neg- off and held it to the pos+ for 10 seconds.

@L80OUS just let the car idle and do it's thing post reset, after 10 mins it's stored the recal map - then go for a drive and run the trans adaptation. I'll be carrying this out on mine when it's out of hibernation, after checking the levels and a wax-buff - it's been 4 months since I drove it last!

 

Ok nice one thanks .....

 

I had exactly the same experience today when I put a new battery into my 1999 XK8.


I understand that it is caused by the need for the ECM to recalibrate after the battery is disconnected.


I drove my car immediately after putting in the new battery and it continued to have the high idle problem throughout my drive. But after turning off the car, and now a little bit later starting it up again, the high idle problem is gone.


Moreover, I find that with my 1999 4L engine there were no resets required after my battery disconnect except the window memory.


Seems that 4.2L engine vehicles have a lot more resetting to do than does my 4.0L.