Problem. In 1 in 20 starts, engine starts fine. Then, when the accelerator pedal is depressed, nothing happens...it just stays at idle !!!!!!! Cursing, jumping up and down, kicking dirt, making obscene jestures at the engine,etc., doesn't seem to help...but..if I wait about 10 minutes (idleing), it cures itself !!!!!!!!!!
Need help.
Thanks, Max
97 F250HD 7.3L diesel. 97K miles.

 

It sounds like your Idle Validation Switch is out of whack. It might need replacement or merely adjustment. If you look at the accelerator pedal, at the top, there's a tab that contacts a white switch. If that switch isn't depressed properly while at idle, it won't release when you apply more pedal, so it doesn't tell the pcm you're moving the pedal. To possibly fix it, shut the truck off, depress the pedal slightly with your hand, to get the black tab off the switch, and bend the tab down slightly with pliers, to make sure it closes the switch when you let off the pedal. Be careful not to put pressure on the switch itself during this step. When you release the pedal, you should be able to hear the click of the switch. Start the truck and try it. You might need to do this a few times to get it right. If it works, great, if not, you'll have to buy the complete pedal assembly, since the individual switches aren't available.
Good luck.

 

Thanks for your quick reply,Mr. Quadzilla.......Appears you are an encyclopedia of knowledge about diesels! I'll give your suggestion a try tomorrow.....we're experiencing some darkness right now.
Regards,
Max

 

Adjusted Idle Validation Switch (IVS) actuator tab as per Mr. G.
The IVS was "clicking on" at about 3/4" deflection..which seemed too much. Bent the actuator tab so that switch clicks on around 1/4". Hasn't repeated the problem...yet!
I'm going from Las Vegas to Chicago this weekend so I hope this is the "fix" !
Max

 

I'm having the same problem with my 2001 F250. However I can hear the switch clicking and it occurs with only about a quarter inch movement of the accelerator pedal. I had just replaced a booster gauge when I discovered this problem. Is it possible I could have disconnected some wiring when I removed the front dash?

 

If the problem is intermittant, it might be that a wiring connector wasn't reconnected properly..might look at each connector that was disconnected to insure good mating and pin retention.
If the problem is constant, it seems that a connector that was disconnected IS THE PROBLEM.......
Since I experienced the problem, I've done a lot more research to learn how the accelerator pedal potentiometer and Idle switch interact with the PCM (powertraim control module {computer}) to schedule the proper amount of fuel to the injectors. Check out this site for some more info.,

http://www.intellidog.com/dieselmann/symptom.htm#pedal

To isolate the problem, you can "back-probe" the connectors at the Accelerator Pedal Assy (use a good digital voltmeter) or a meter with a 10Meg ohms/volt or better and measure the voltage at the potentiometer (variable resistor=variable voltage). You can also do this to check the IVS (idle validation sw.).

I haven't figured out how to attach "stuff" to this forum yet so here is an explanation of what to do. I have electrical schematics for my truck (1997) but the circuit should be the same.
The electrical connector at the pedal assy for the ACCELERATOR VOLTAGE has three wires attached. The color code is:GREY with RED stripe=GROUND. GREY with WHITE stripe=variable voltage to PCM proportional to the amount of accelerator pedal deflection.
BROWN with WHITE STRIPE=5.0 VDC reference voltage from PCM.
To check for proper operation of the potentiaometer, do this:
Place the BLACK probe of the VOLTMETER into the back of the connector pin that has the GREY/RED wire. Place the RED probe into the pin that has the GREY/WHITE wire. Turn the ignition switch ON but don't start the engine. At the idle position of the pedal, the voltage should measure LESS THAN~1.4 volts DC.
A good reading will be between 0.6 volts but no higher that 1.4 VDC.
Now depress the accelerator pedal all the way to the floor. Voltage should be no higher than 4.5 VDC. Now vary the pedal position between IDLE and FULL Throttle (VERY SLOWLY). The voltage should increase at a "linear" rate toward 4.5 VDC with no hesitation or "jumping around".

The IDLE VALIDATION SWITCH connector has two wires connected to it. One wire is BROWN which is 12 VDC from battery.
The other wire is RED with an ORANGE stripe...which goes to the PCM. To check the switch. connect the black meter probe to CHASSIS GROUND......Connect the RED meter probe to the RED/ORANGE wire on the back of the connector.

Voltage should be ZERO VOLTS. Now slowly depress the accelerator pedal until you hear the switch "CLICK". ....the volt meter should 12 VDC.

If these checks are OK, then the problem is somewhere in the wiring between the ACCELERATOR PEDAL ASSY and the input to the PCM. The rest of the wiring to your PCM may be different so I'll not include it.
Man, that was long-winded but hope it helps.
Good luck, MAX

 

Ya know, when something goes wrong with my truck I always think the worst. And I never blame it on myself. Incidently, thank you for your assistance. This morning I fixed the problem, fuse #19!!!!! I got in the truck this morning to start it up and see if by some miracle the problem was fixed. I happened to notice that the fuel gauge said empty. javascript:smilie('')
Well, that's odd, I just filled it the other day. Ah-huh! The other gauges weren't working either. Better look at the owners manual. There it was. Fuse #19 protects the instrument gauges and the PCM!!! Could it beeeee?? javascript:smilie('')

Well, to make a short story shorter, that was the problem. Thanks again. Sure glad I didn't have to check all those voltages.

 

QUADZILLA....put 4,400 miles on my diesel in the past 7 days going from 'Vegas to Chicago and return. Truck ran perfectly with no problems with the "accelerator pedal response".
You done good!!!....thanks again for telling me what to do to fix it!!!!!!!
Max