Alright my car has just recently started this trend. The other day i decided to take the condenser off seeing how i don't have a/c. Put everything back together and it started to get a lil to warm (193 ish). So i take the thermostat out and problem fixed until i get the OEM one in.
Now my car idles but really poorly like it is missing. Starts fine when cold or hot. iam running pre-mix. the car is a 90 model turbo 2 with s4 engine.
Thanx in advance!

 

Might be a lil confusing i have no thermostat in rigt now.

 

So you didnt have the OEM thermostat in to begin with?

Why put an s4 motor in an s5?

That aside, im willing to bet you accidently disconnected or bumped something while removing the condenser. Check for good spark on all plugs

 

Money was the reason for the engines. I did have the a stant t-stat but took it out after that happened. Not running a t-sta now until i get the oem one.
Spark is good on plugs. could it be carbon???

 

Well its not related to the problem you're having now anyways...

Check for air leaks after the MAF? Wherever you were working at under the hood, go back and check to make sure everything is connected and hooked up correctly... seeing as you say it started after you did some work on the car

 

Yea, i just took it for a drive and the idles surge from like 500 rpm to 1200. anything above that is pretty smooth.

 

you might have some air in your coolant, the bac has coolant running through it and might cause it to surge. it might be causing inconsistencies with the idle.

 

Didn't know that!? huh! i'll be damned.

 

I thought oh, **** it must be a apex seal then cooler heads prevailed after i saw that i still had power in the rpm band.

 

everyones so quick to assume blown motor :P

heh, i've thought my motor was blown numerous times now too though

 

The BAC is not a coolant-controlled device like some Hondas. The coolant circulates through the bac ONLY to keep it from icing up in cold weather. The thermowax unit controls fast idle speed during warmup and is affected by coolant temp. Keep searching for vacuum leaks or disconnected/ misrouted hoses.