i have a huge problem, or atleast i think its huge. my 1988 audi 90 quattro feels like its out of gas and the revs just drop and go back up (like youre on your last drop of gas) absolutley randomly!
can anyone tell me what it is and i how i can fix it?

 

OK these are just suggestions as i had similar problems on my honda and BMW. Try draining the gas and running high octaone(premium) gas and put in some injector cleaner. also check the plugs and plug wires and replace if needed. on my honda the same thing happened to me and it turned out the plug wires were old and cracked. on the BMW my dad ran cheap gas and it messed up some sensors. so maybe runing high octane gas and new plugs and wires(and injector cleaner just incase) might fix this problem. the BMW still has wierd revs when i start it up but it stableizes in a few seconds.

 

I am not sure my first instinct would be to drain the fuel tank, although it maybe necessary if there is major contaminents in it (i.e. water, sugar, etc.).

Anyway I would (depending on when the MX was last done) change the fuel filter, the air filter, plugs and wires and possibly the O2 sensor. The fuel injector cleaner and possibly an octane booster is a good idea (I would go with name brands such as Lucas or STP). Examine the spark plugs when you take them out an note oil, too lean/rich mixture, etc.

I think that all of this should set you back about $50-100 depending which plugs and wires you get.

Brian