99 A6 Avant 2.8 wagon won't start after long run!

It is your battery cable. Take a look at it. There is a main wire and there is a second one that feeds the computer. Take the screw out and clean the whole thing with sanding paper or metal brush.

It is that simple.

Problem gone? I had the sa me thing going and the dealer of course run it through a computer that gave no answer. Later they wanted to replace numerous relays. HOLYYYYYYYYYYYY!!!!!!

Or

Just move ecu left and right untill check engine appears.

Thanks, Dick Harder. Tried the trick you offered, it worked a bit. Now the starting problem is more unpredicatable, since you never know when it will not start! At 1st I thought it was when engine was hot but now sometimes it won't start even when it been cooled for half an hour. What's more, the engine check light lits on and off, its not blinking but stayed on for a day and it might go away in the next day. So I don't know what is going on now. I think I will let it be that way to see what will jump out of box.

Oh, when you get a hard start, you can hear the engine cranking hard and then if you hear the puff noise like you lack of gas, give it a little throttle, then it starts. Have no idea whats going on!

Bloomsburg

If pressing the gas pedal helps it start it might be that adding air is clearing a flooding condition.

Flooding could be caused by leaking injectors. Try a bottle of Techron injector cleaner in your next tank of gas.

Thanks, sure will try that! Appreciate your help!