High idle 351w

jklapp86 · #1 (**permalink**) 06-18-2008, 01:00 PM

I have a 94' f150 with a 351w and intermittently it will have a high idle (1000-2000rpm's) it will do it at start up and after cruising, could a vacuum leak cause this? any info would be nice, thanks in advance.

jklapp86 · #2 (**permalink**) 06-20-2008, 07:46 AM

Could the intake runner gaskets be leaking causing unmetered air to enter intake?

Conanski · #3 (**permalink**) 06-20-2008, 09:20 AM

Yes, that's possible. Has it shown the check engie light anytime recently? It's a good idea to pull the codes anyway, Ford Fuel Injection has a simple DIY proceedure for this. A sticking IAC or faulty TPS could also cause this.

jklapp86 · #4 (**permalink**) 06-20-2008, 09:58 AM

i had it at our shop yesterday and i pulled codes, no codes and we got it to idle high in the shop, unpluged the IAC and it idle down to proper level. So we came to the conclusion it was being commanded that way ruling that out, we did find that the canister vent solenoid seemed like it was sticking, i would have vac. at elevated idle so we unplugged it an still there was vac, according to the ford WSM that solenoid it only suppose to purge when grounded. could that cause elevated idle from being in a constant purge state?

IcemanV8 · #5 (**permalink**) 06-20-2008, 12:55 PM

If you unplug the TPS, does the idle come back down to normal? Try that with the IAC plugged in.

Sounds just like what my 302 was doing with a bad TPS. Only difference.... mine showed up when I pulled the codes. That's what leads me away from it being electronical, unless it was a user mistake pulling codes, or it didn't have time to show up in the codes, yet.

How "I" check the code reader is by having the engine running, unplugging the EGR, let it run a few seconds, plug it back in. It should show up on the code reader. If not, something isn't working, or you may even have a bad computer.

Conanski · #6 (**permalink**) 06-20-2008, 01:05 PM

Yeah.. if you unplug the IAC and it idles down I'd suspect the TPS, it may have a dead spot and be giving the computer bad info. An analog multimeter will show this as you sweep the throttle through it's range, http://www.fordfuelinjection.com/?p=30

jklapp86 · #7 (**permalink**) 06-23-2008, 10:06 AM

When i pulled codes on the vehicle i did it with the old ford NGS system tester. Had our senior master tech aid me in trying to diag. the cause so it wasnt a human error plus it showed up codes from us unpluging the egr and such when we were messing around. Sound like a TPS but without the codes.