Hello. I recently bought a 90 Formula 305 5 speed. Stock tbi stock heads and stock cam. Car had a chip burned to eliminate vats. Car just had new head gaskets, new reman TBI unit and new injectors(stock) put on and headers installed all at the same time. Smog was deleted. Car has a new fuel pump. Car idles very high, around 1200 rpm even when warm after driving . Car ran fine when it was stock, the old tbi had a bad injector and leaking throttle shaft so the tbi unit and inj was replaced. Car has new plugs,cap ,rotor, wires tps IAC. Fuel filter was done last year, I will replace that to see if that is causing the high idle. Maybe a vaccum leak or egr. Has open elelent air cleaner. I want to buy a stock air cleaner back on to help eliminate that Car has 02 sensors still.

 

If the thermostat was replaced with a lower temperature unit put a 195 back in. If the IAC steps (scan tool required) is at zero then look for a vacuum leak.

Note that the fan isn't ECM controlled, so can't burn a chip to lower the fan on/off temperatures.

RBob.

 

I will check the thermostat and Iac. Will the headers make a high idle with the stock 02 sensor? Will a heated 02 help at all. The previous owner did a vacuum check with spray. I will try to have a smoke test done to find the vac leak. Thanks for your help.

 

Have you tried just resetting the IAC?

https://www.thirdgen.org/tpimod2/

 

The o2 will help with idle air fuel mixture in closed loop.
A common place for a vacuum leak on tbi is the base plate on the tbi unit .
You might want to run a afs-74 o2 but it’s not the cure for your issue of high idle.