Not sure how much info you have or your backround so please bear with me.
Ok so as you know P0121 is TPS to ECM fault
P0172/P0175 could be incorrect signal from
ECTS Engine Coolant Temp sensor
MAFS Mass Air Flow sensor
IATS Intake Air Temp sensor
TPS Throttle Position sensor.
As P0121 is the most common error perhaps TPS to ECM is the main fault, however you say the problem is at its worst when driving slowly and I asume the engine will be at its hotest. When you put the air con on the fans cool the engine more and the error goes away.
It may be worth checking the temperature readings on the ECTS, MAFS, IATS to eliminate a wrong temperature reading causing the engine to adjust the fuel/air mixture.
I asume you have a obd code reader, free software is available to obtain the readings required via a laptop.
If all temperatures seem ok then its down to wiring fault between TPS and ECM or faulty ECM/TPS
Again sorry if this is going over what you know and have done already. Good luck.
Friday, June 25th, 2010 AT 9:12 AM