Has anyone encountered this?: At 50 + mph, especially on highway - throttle completely off causes engine stumble, rpm +,- approx 200 oscillation and mpg display to go to series of dashes. Other data/info displays are not affected. Slight throttle application restores normal behavior but MPG display recovers at 199 mpg and then resumes normal.

I'm thinking loss of throttle position and/or fuel flow input freaks out computer, and when it is recovered the computer thinks it traveled a long distance with no fuel flow.

early production stock 1999 A8 Quattro.

Any thoughts/suggestions?

 

Hi
The readout of the MPG going to ---- is quite normal. it only means that it is outside a value that it can display with the number of characters it has. Any A8 will display ---- if you lift your foot off the gas pedal when at a reasonable speed, you are just doing lots of miles to the gal. The revs jumping up and down (if I read your post correctly) is something else though... unless you are just talking about the tranny downshifting because you have lifted off the gas? Then otherwise the most likely culprit is the MAF. This tells the car's brain how much air is going in to the engine so that the gas mixture is regulated correctly with changes in temperature, car speed etc. When the MAF goes bad, it can cause all sorts of strange throtle shifts etc. Hope that helps?

 

As a follow-up post.... the throtle system actually has two sensors that both send a position signal. In this way if there is a problem with one sensor (say showing full throtle) the other sensor does not. The ECU monitors both outputs and if different puts the car in limp mode with the engine fault symbol on the dash. So, it is not a throtle position sensor problem.

Hope that helps?

 

Thanks burb. I will look into the MAP - the rpm oscillation and stumble are not OK