Audi 90 5cyl revs fluctuating up and down

You can take it to most auto parts stores such as O'Reilly's or AutoZone and they will scan for diagnostic trouble codes (DTC) that may be set in the computer.

Hello James,

If the engine revs up with no increase in speed, your clutch is slipping. Probably the reason the car was sold!

Alan.

It could many things, please go for a scanner test

check fuel filter and check air filter

Transmission problem need to rebuild.

Had the same problem until I replaced the crank sensor.

You need to have OBII scan performed. The fluctuating idle sinus like a MAF sensor, Temp & fan are separate issues. Get scan done, that should identify exact issues.

Sounds like you have an air;lock in your cooling system.Try placing a bleeder on the return hose to the heater core ........looks like a small tap

The oil pressure guage will fluctuate with engine RPM. At idle it should be approximately 20 lbs./sq.in, at high revs about 50-60 lbs./sq.in. Hope this helps any concerns you may have. Good luck!

Here's the thing. The ECU will shut down AC if the engine temperature is too hot. If the coolant temperature sensor is malfunctioning (lying to the ECU) telling it that the temperature is hotter than it actually is, the computer will turn the AC OFF.