My 1991 Pontiac firebird is due for an emissins test. It has been hesitating on acceleration at low speed only when cold.
A mechanic friend connected a special monitor to the car and read a code 35(IAC problem). One sevice manual I have states to replace the IAC valve. Another says it could be either the IAC valve or TPS sensor. Upon checking the TPS visually ther is a wear patern where the shaft is inserted. Do you feel I really
have to replace both,or is it the IAC valve,which was replaced
2 years ago and allways worked well previously?

Frank Korinko, October 2005

Before rpalcing the IAC try taking it out and cleaning the pintle on it and housing it came out of with a good carb cleaner ....
when you pull the iac out look at the pintle and see if its been seating right ....there should be a sign of wher its seatiing on the pintle seat ....
tps needs to be looked at with a scanner ...to see volt movement when you press on acelerator...
most likely hav a carbon build up

bg, October 2005