friday morning I started my A4 98 Z28 and drove about 4 miles hardly reaching 40 mph. at a red light I stopped normally, slight downslope, and when I left off the brake a little the car seemed to lurch/buck forward and a very dull sort of clunk came from the back. I immediatly thought it was the trans. continued on and drove fine but did this again 3 more time till I parked at work. I was bummed, 4 thousand mile in 2 month NEVER any problems. It really gets wierd, 8 hours later I left work planned on taking it back to where I had tires put on on Tuesday to see if he did something, the Z28 ran perfect and has been perfect, no reoccurance of this since all weekend. ANY IDEAS????

 

ttt

 

Could it be misfire ? If it loses pull and comes back the rear can give a clunk. How much from last plug change ?

 

plugs, I don't know. bought this car with 31,500 miles in june and now has 35,000. I've driven it even more, ALL WEEKEND, and has not come back. However, what other things would I experience if the plugs needed replacement? I read a lot in here and saw many posts/replies about detonation. I have definatly heard that from the exhaust(flowmaster) at certain times. Thanks for the idea...I want to have this car a long time!

 

I started experiencing little roughness at idle and sudden rpm drops gear on at lights at 25k. I also felt WOT didn't sound clean. Pulled the plugs and some of them had lost a piece of metal which belongs to stock plug design. Dunno if your symptoms are becouse of this but I would imagine large plug gaps could give symptoms when the weather is right for that. If and when the stock plugs loose that piece of metal the gap widens maybe 50%. Usually stock plugs are done after 20k.

Detonation, or is it the popping when you ease the throttle when coming to a stop ?
That would be just typical.

The stock plugs lasting 100k is BS. Change the plugs anyway so you can rule that out if it happens again. And change them yourself so you can be sure that PITA #8 plug gets changed.