How can I repair my 91 Firebirds cold hesitation?

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