A couple of weeks ago, the fuel gauge on my 940 turbo began acting erratically. This was shortly after I replaced the fuel filter.

The gauge works perfectly if I turn the key to position II. If the engine is running, however, the gauge will begin to fluctuate between empty (with the warning light on) and about 3/4 full. Also, below ~1/3 of a tank, it seems to work perfectly.

So far I have tested the sender and it seems to work fine (I pulled it out of the tank and checked the resistance at various positions). I've also resoldered the connections on the gauge board, and the 3 screws holding the gauge to the flex PCB on the back of the cluster.

I'm at a loss as to what to do next. Replace the gauge? Could I have disturbed the wiring when I dropped the fuel pump to change the filter? Is some electronic device on the car interfering with the gauge function?

Thanks,
Eric