I recently installed full exhaust on the 'ole '90 Formula TBI and now I am having idleing trouble. The idle will dip then surge and repeat this and sometimes stall out. It seems to do this mostly when the car is warmed up. What could be causing this? Could this be a timing issue? I had the timing advanced 8* when the car was pretty much stock and it ran fine. Also there doesn't seem to be much gain in performance. Is the car running too lean now with the new mods? Advancing will lean the fuel mixture right? I am pretty frustrated with this. Thanks.

 

Did you make sure that all plug wires were routed properly? It is very easy to cross a wire and have it on the wrong plug. Also, check all vacuum and sensor lines and ensure that they are all hooked up. I would also check for exhaust leaks. Pay close attention to the header flange. A leaky exhaust header (via AIR or head flange) will disrupt 02 readings and could cause your car to run improperly.

FWIW I would set your stock timing to 0° or 4° advance. 8° is too much and is not needed with the stock swirl port heads.