For 2 weeks, my 2003 A4 B6 1.8t manual shift will intermittently give a little sigh of hesitation. It clears right up after a few seconds. This is worrisome as it feels like when the car runs out of gas, except very briefly.

I have searched and found suggestions which I plan to try. But I did not find this exact problem described.

Done so far:

Code scan - 16684, random cylinder misfire, 16685 cylinder 1 misfire. Both can be caused by fuel supply or fuel pressure issues

Cleared codes, problem persists with no code set, yet

Replaced fuel filter which has internal pressure regulator

Added Seafoam to gas and filled tank to clean injectors


I have more things to try but I thought I would ask if anyone has advice or experience with this to share?

And how can the fuel pressure regulator be in the fuel filter? How does it get a signal to vary the fuel pressure?

Thanks for your input.

 

Here's an update. The problem only seems to happen when the gas tank is half full or less. When the tank is full, no problem.

Does this ring a bell with anybody?

 

Solved - brake light switch!

I noticed that the ESP light came on frequently. Searches found other posters where the brake light switch failure will cause an intermittent loss of power. Other symptoms I had include lack of cruise control but tapping the brake brought it back; ABS brake system VAG COM code 00526, brake light switch.

Replacing the brake light switch has fixed all symptoms so far after 3 days. I need to drive for a week more as the problem was intermittent.

I believe the connection is that when the brakes are applied under certain conditions, the ESP reduces engine rpm to a high idle so the engine will not pull on the brakes. With a bad brake light switch, the ESP thinks the brakes are applied and when those conditions prevail, it cuts power to the engine.

I hope this helps others with this mystery.

 

After two months, the car is symptom free, so it was the brake light switch.

Tip: Don't mistake the clutch switch for the brake light switch. They are very close to each other.