Buford T Pusser

Bought a new car battery a week ago. Now the idle does a weird thing at the low end. Help?

The original battery was on its last legs in my car so I put in a new battery.

It started right up, but is doing something strange. When I let off the accelerator when idling the RPMs jump down to about 200, then bounce up to 400, do a bounce down, go up to 800 and ends around 1000. This process takes about five seconds or so.

It's like the car is going to stall but it doesn't. Anyone know what the deal is with this? I have an 99 Audi A4 w/the 1.8 Turbo.


I've tried these fixes:


1. Disconnect the battery for 10 minutes. Reconnect it.
2. Put the key in and turn the thing to run. Leave it there, unstarted, for 3 minutes.
3. Start the car. Let it run in idle for 3 minutes.
4. Shut 'er down. Computer should now be reset.




1) remove both the Positive and teh negative battery terminals from the battery.

2) Wait 15 seconds then touch the 2 removed battery leads together and hold for 10 seconds then seperate. (This immatated the same capicitor discharge that is involved with the Vagcom reset)

3) replace and reattach the terminals to the battery

4) stick key in ignition and turn to ignition on (DO NOT START THE CAR) and leave in this position for 30 seconds to allow the newely reset computer to re-learn the parts of your vehicle.



(I noticed a few thread about this, but the thread starters never came back to tell what worked for them. )

JAFO

what year and engine?

Greyhound Guy

Is it just low or is it irregular?

RKA

Get a vag.com and perform a throttle body adaptation.

Buford T Pusser

What's a vag.com? (excuse my ignorance, but it sounds gynecological)

Buford T Pusser

The idle is about 1000K but before that it does the low thing when stopping or sitting there and revving the engine. It starts low and corrects itself but the engine will stall if it's a sudden stop or the A/C is going.

It's a 99 with 74,000 miles. 1.8T

Buford T Pusser

99 w/1.8T and 74,000 miles.

RKA

in the absence of the vag.com, take it to the dealer and ask them to perform a throttle body adaptation. That should cost you 1/2 hr or 1 hr of labor, even though it only takes them 5 minutes. That syncs the ECU with the throttle body. When the power was disrupted, that information was lost. The ECU no longer has precise control over the throttle plate, so at idle you're noticing wierd things happening.

In theory, putting the key in the on position without starting the car or touching the accelerator, for a few minutes *should* also result in the car doing a TBA, but the success rate with a vag.com is 100%. With the key in the on position, it may or may not work.

Greyhound Guy

Well you mind as well do a TBA and idle adjustment with a vagcom.