Hey all..

Gonna talk about my F-250 today. When I bought it, the owner said it didn't pass emissions testing. It also has a seemingly sticky throttle issue. When I give the engine some gas, and let off, it will act as if I'm still giving it gas for another second or two...like there is a delay. I've put 600 miles on the truck since I bought it, and its been consistantly like this, no change in the way it does it.

The throttle linkage looks ok, seems to return ok mechanically, so I don't think it's anything with the linkage or TB. I get a quick flash of the red "engine" light from time to time, usually when under a load, havn't been able to determine when it does/doesn't flash, it's usually just a quick flash. I checked the computer codes w/o the scanner, and all I could see was a code 35. Any input?

 

according to the repair manual, code "35" is evp circuit above maximum voltage.

 

If the code 35 is a KOEO code, it is easy to diagnose. Just backprobe the EVP sensor wire with a voltmeter. It should be a fairly low voltage -- say 0.5 volts or so. The computer is complaining that from its point of view the voltage is ridiculously high -- maybe 4.5 volts plus. Inspect the wiring while you are in there. An open circuit on EVP or an open SIGRTN to the sensor will result in this code.

If the code 35 is a memory code only (only gets set when driving), it gets to be more work. There is a chance there is a "dead spot" on the potentiometer. You can take the sensor out and move it manually, watching the voltage as it goes through the full range. A sudden jump in voltage tells you there's a dead spot.

Or you can just swap out the EVP. Beware that there are two kinds, a gray one and a black one, and they are different from each other -- although mechanically the same.

As for the slow return to idle, I would check the TPS (0.98 volts with throttle closed and no dead spots). Also remove and clean the IAC valve. Consider cleaning the throttle body as well. Some of the Ford throttle bodies were lined with Teflon and have a "do not clean" tag on them. If really dirty, it is OK to GENTLY clean these, with a soft rag and a mild solvent.

 

I'm going to just swap the TB off my 302 instead of cleaning it....

Where is the EVP sensor?

 

On top of the EGR valve(left of the TB). There's 3 small bolts holding it on. It has a wire harness going to it.

 

I havn't had time to check into this stuff yet, I got sick this weekend and it's been really cold. However, my 89 sat for about a day and 1/2. I went to start it this morning to go to work and it started just fine, idled ok...took off down the street, and when I pushed the clutch in to take a right turn, the engine died on me. Started it back up and took off, and I realised that it ran fine if I was driving it. However, if I pushed the clutch in as if say I was coming to a stoplight, the RPMs would come down like normal but they'd keep going past idle and the engine would die. It simply would not idle, I was able to drive to work ok and when I got to work I parked it and shut it off. I started it back up and it idled ok...said to myself dang that was weird, and went into work. Drove it home just fine....no check engine light or anything...think that is related?

 

That situation has happened to me once more since, drove it for awhile and then all of a sudden it wouldn't idle again, then after awhile it came back and worked ok.

I went down to a shop i know and had my computer codes read on a snap-on scanner.

I got these (he called them "fast codes"):

12 - can't control RPM during hi RPM check
44 - Thermactor air system not working
77 - Operator Error - Throttle not snapped

I think 77 is because he didn't push the throttle in the middle of the test. I wasn't expecting 44 so maybe I have to check for a thermactor problem. 12 I can't explain (I've looked at the brief descripts in my manual for these already...).

For continuous memory, I got code 35 - EGR signal too high...

Apparently because it's a CM code, it's an intermittant problem.

Any input on these codes and my situation?

 

code "12" check [ iac ] valve check voltage with voltmeter, with key on engine off
voltage at iac should read about 10.5 volts if so it's getting the proper signal from pcm.
if it is getting the proper signal, check the iac for excessive carbon. clean the iac and check the resistance of the valve should be between 7 and 13 ohms

 

I have the Iac freeze in Cold weather usually after the engine warms up they work. I would at the very least clean that iac and would give serious consideration to replacing it.

 

35- EVP circuit above max voltage... Could be a vacuum leak, a bad EVP sensor, a dirty EGR valve, or maybe some bad connections.