I've been battling a problem with my 92 F-150 4x4 302ci. Idle is very eratic, will not upshift properly, dies when approaching a stop sign, etc. I have replace the Idle Air Control valve, reset the computer and it's no better. While troubleshooting last night, I disconnected the IAC valve and the EVAP purge solenoid. The thing idled perfect, I installed the IAC valve and left the purge solenoid off and it's fine. I hooked up the vacuum line from the purge canister directly to the Throttle body vacuum port, (where the purge solenoid was) I left the air cleaner assemble off, but drove the truck and it drove great, other than a firmer than normal shift. Could a bad Purge Solenoid have been causing my above problems? That is the conclusion that I have come to, but it doesn't make sense after I researched what the EVAP system does.

Any thoughts????

Thanks,

Jon

 

evap vents fuel tank fumes from the tank to the engine to be burned. sounds to me like TPS sensor is going out.