alright so i start my car up...i let it idle for about 10 seconds and then all the sudden the rpms drop down and my car would stall (unless i keep a steady foot on the gas, the car will stay on). also, i would be driving my car and flooring the gas and my car would move like a turtle. anybody know what the problem is?

 

compression test

check for codes next

then check the intake system for hoses knocked off, cracks in hoses or vacuum lines popped off.

 

fuel filter?

 

could also be limp mode if it is an S5, need more details... does the CEL come on when it does this?

 

Did you find a solution. My 86 non-turbo started having the same symptoms a week ago. Throttle position sensor measured bad so I replaced it, replaced the fuel filter, no error codes showing on the LED's I hooked up, no check engine light. I'm considering having the timing checked before I start replacing vacuum lines one by one. I didn't see any noticeable problems with the vacuum lines I could see.

 

TPS or Vac leak