So many questions to ask....
 

Hi everybody, I need all of your collective wisdom! I have a 1988 944s which I purchased a few weeks ago. I have a couple of things going on and need help.

Fuel gauge - sometimes 3/4, sometimes 1/2 sometimes just below

Odometer - not working, took out moved white worm drive with thumb, odometer clicked over and the notorious gear looked ok, worked for 12 miles and now stopped again.

C.o running at 1/2 %, is this right, seems a bit lean to me. AFM does not seem to adjust by much and can't see, hear air leaks.

Knocking when taking up drive (bit like back lash in a diff) going forwards and backwards

Other than that she's a peach! Loving having a 944 just need to understand it!!

Odo drive: theres a drive gear, usually orange colored, that goes bad due to age and is easily replaced when the gear cluster is removed. BTW, don't reset the odo while the car is moving. Fuel gauge inaccuracy is a common issue. Not sure if replacing the tank sensor unit is the answer. I've hear yes and no on this.
Knocking: I'd recommend jacking up the car and checking the hole where the clutch wear is checked. Put finger inside and see if there's pieces of rubber in there. It could be the rubber centered clutch is failing.

Common problem with the fuel gage. It is the sensor in the tank. There are a few posts as to "how to" fix this.

Try this: put the car in 3rd gear, engine off. Push car forward and back, rock it a little in each direction. If you can hear a click from the bellhousing area (back of the engine) under the middle of the car, that's the limp tabs on the clutch disc engaging. Means the rubber center is done - I'm with mytrplseven on this one. Lash issues like you describe are usually rubber-centered clutch related.

I find my fuel gauge moves faster the more I drive...

Worm gear can move on shaft and not properly engage even though it looks ok.