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Joined: 14 Oct 2008
Posts: 118

PostPosted: Tue Jan 13, 2009 7:46 pm    Post subject: question for the experts Reply with quote

hello to all...went away for christmas and had to leave the car parked...as the car was not used and the weather was unseasonably cold, the battery died and the car had to be jump started...all seems fine however, there does seem to be a 'possible' performance issue...ie, when i 'put my foot down' a delay is noticed...maybe i am being silly but i was wondering if i should get it checked or just keep an eye on it...any helpful advice?
i thank you, and my car thanks you!
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Joined: 05 Nov 2006
Posts: 5668

PostPosted: Tue Jan 13, 2009 11:38 pm    Post subject: Reply with quote

Hopefully someone will be along eventually to help further, but I have a recollection that you have to be very careful jump starting a lot of modern cars in case you spike the ECU...

If this has happened it should show as a fault code on the diagnostics - I suggest getting a friendly Indie to do a quick check for you just in case.

For future reference, I have been told that you should use the positive terminal on the battery, but connect the other lead to somewhere connected to the chassis earth no closer than a metre from the battery.
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Joined: 14 Oct 2008
Posts: 118

PostPosted: Wed Jan 14, 2009 7:19 pm    Post subject: Reply with quote

thanks for the input...would something not show up on the display?
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Lloyd Six

Joined: 04 Nov 2008
Posts: 879
Location: Worcestershire

PostPosted: Sun Jan 18, 2009 6:31 pm    Post subject: Reply with quote

I will keep this brief as I am posting from a mobile.
Cars after 2001 and some before that date are OBD-II with adaptive, self learning. Not only do they learn about your driving style but they also adapt to the changing values on the engine.
For example: the mass air flow sensor can slowly change in value (value = the voltage sent back to the ecu) with age. The ECU learns and stores this data along with data from other components plus how heavy your right foot is!
This data is stored within lets say capacitors. When the battery is disconnected or looses charge that info is lost and it returns to factory pre-settings. This is where your problem is.
The ECU is expecting value X but receiving Z.
This will sort itself to a degree over time but if you want an immediate fix its simple. . Follow these instructions: (from cold)
Disconnect battery for 10 to 15 mins
Turn ignition on so all lights come up but dont start, leave on for 1 minute
Turn off ignition for 10 secs
Start engine but do not touch acc. pedal
Let the car idle for 10 mins then jump in a go for a drive, the harder the better, after a good thrash pull to a safe stop, turn off engine then restart. . Job done, ECU is reset, base idle settings and data is restored.
The car should now be better than ever.
Currently - Audi A4 Cab & BMW Touring.
Ex = 2 Boxsters and a very missed Black 996 C2 facelift Sad
Coming soon... either a 997 or 996TT
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