Idle problem after jump start

[Mossyboy1978]

I took the car for its MOT today - sailed though which is always a bonus. No idea why I always get so nervous at MOT test day...

Unfortunately the lights drained the battery and it needed a quick jump to get going. Obviously getting to the battery what a royal pain in the ring but once jump started the car started searching for an idle speed between 1500 rpm and 1800 rpm. It did this for about 5 mins and then settled at a very fast idle of 1500rpm. It slow a bit when i drove it out the workshop and then once I turned the car off and on again, it found a nice 1100 idle immediately and stayed there, only dropping to 950rpm once a bit warmer.

Any clues as to what has happened? Is this normal after a jump? Or did I fry the ECU with a power surge of some kind?

[Dr Mike Oxgreen]

I be betting on a slight break in a wire in one of the looms you had to move out of the way to get to the battery.


Not quite sure how I lapsed into pirate-speak, there. Aaarrrrrr!

Edited by Dr Mike Oxgreen on Tuesday 22 May 12:55

[paulathome]

Hi, just disconnect your battery for a few seconds and then reconnect. This will clear the ECU of any fault codes that might have popped up after your jump start.
Then start your engine and let it learn the new idle speed for 5 minutes.
Paul

[Mossyboy1978]

Oh god that's going to take hours to find isn't it?

[TVR Beaver]

I've seen this before after the ECU has been disconnected or I've had the battery out....
It's like the ECU has to re-learn the tickover RPM??... It usualy correct itself after a number of cold starts... See how it goes

[Mossyboy1978]

paulathome said:

Hi, just disconnect your battery for a few seconds and then reconnect. This will clear the ECU of any fault codes that might have popped up after your jump start.
Then start your engine and let it learn the new idle speed for 5 minutes.
Paul

Thanks Paul - my car actually has a cut out switch on it so when I turn the car off it kills the power to everything all together not just the ignition. Will this have the same affect and possibly explain why it was peachy after I turned it off and on again?

[paulathome]

Yes this should have the same effect. So long as the ECU has its power removed to clear the fault logs.
Paul