hey people,
I have 98 audi a6 that was sitting for 1 yr. I use to drive it, ran perfect. Te battery died since i neglected it. When I replaced and started the car, it would shut right off... Then when I start and keep my foot on the gas a little, it will stay running. If i slowly let off it will catch, but after a few minutes the rpms start going up and down and the car just shuts off. Any tips? Is there a way to reset the computer on the car? Now a check engine like has come on, but I dont know what its referring to yet... Thx in advanced

 

vag-com is your friend, or obd2 , scan your car.

 

Forget obd2 - VAGcom is your only friend! --

PS It is most likely a vacuum line..

 

Also, you may want to check the ICM (Idle Control Module).

Try to start the car with the ICM disconnected. It may be revved up, it may not, but it should have a smooth, "liniar" sound.
Connect the ICM back and see if the RPMS start fluctuating again. If you experience again the same fluctuation, then your ICM went bad.

 

Most probably it is your spark plugs... one of the cylinders is misfiring...

 

Typically, when a cylinder misfires or there's a fouled spark plug, one should experience rough idling, sputtering, and not up and down RPMs. Another sign for a fouled spark plug (or plugs) is when the car starts after some prolonged cranking, especially with a brand new battery.
RPMs going up and down and then engine shutting off on its own is more of a bad ICM symptom.
Then again, Audi may be different... a whole vacuum (of knowledge) in itself...

 

After 1 year sitting in the garage it is possible that the gasoline started to separate (unless you used Stabil or something similar). The water in the gasoline may be partially clogging the gas filter and the injectors.
A new fuel filter may be in order, as well as new gasoline and a good injector cleaner. You may want to inspect your plugs and see the tell-tale...

 

Thanks for all the tips, will definitely investigate. Where is the ICM located, (idle control module) I'd like to try chefro's suggestion. Is there someplace that shows like a schematic of under the hood? diagrams of where everything is? Not sure if they have that, but I am no where near a mechanic.

 

Kev, I don't have a diagram as I don't possess yet a Repair manual.
However, you need to look for something like this :



On my 1995 is right under the air intake tube, close to the engine block/head:

 

Great! This will be my saturday morning project... Thanks for all your help, I will keep you posted!