My 520i (M20 - 1990) Has a bad running problem. I had the cambelt changed and a service, now the car runs WORSE than before, with power loss and sometimes stuttering acceleration.

The AirFlow Meter had been mentioned, but I'm not so sure... it wasn't as bad as this before, the mechanic attempted the adjust the tappets, but they are as noisy as before could this be the problem?

Thanks in advance for any advice