First let me describe the problem on my 91 F150. I've seen threads on this issue before but nobody seems to post final results or if the issue ever gets resolved, and there were always a lot of possibilities as to what it could be.

Anyway, after the truck is warmed up and I've been driving it for a while [at least 20 minutes], then shut the truck off and start it back up shortly afterwards [like if I shut it off to get gas or only need to be in a store for a few minutes], the idle does not remain steady. The engine will rev from about 500 RPM to about 1000 RPM. It only does this when at normal operating temp, but if the truck sits long enough to cool down but not completely cold, it won't do it. I suppose I should try to narrow down the time it takes for the idle to return to normal.

I'd like to get this resolved before winter, and I think a KOER test will be helpful in getting it done, but I'm not clear on all the steps. I'm also planning to test some sensors after doing the KOER test as well- the specific list to be determined after reading my service manual to find all the sensors/components that could be related to the problem- as well as suggestions from you guys. Anyway here's my questions- they're in bold below the steps I'm not sure about.


1. Start and run engine at 2,000 rpm for two minutes to bring the engine up to normal temps and warm up the Oxygen sensors. The engine must be at least 180F (82C) to pass.

Does the engine have to be warmed up this way, or would the test be more effective if I drive it around to warm it up, and is there a max amount of time I should drive it? [I'm thinking a drive to my parents house would be good as my dad has good tools I can use if needed and it's about a 45 minute drive.]

3. Check the Base Timing and make sure the computer is controlling the timing before continuing with test.

Timing light okay for this or should I physically check to see that the timing is right?

7. After the engine ID code you need to test a few items for the computer. You’re vehicle might not have any or all of these items to test.
b. Power Steering Pressure (PSP) switch, quickly jerk the steering wheel one-half turn and released.

Does it matter if this done to the right or left? [Should probably make sure I have the switch first. ]

9. After many tests the computer will flash once, indicating a Dynamic Response test. This single flash is prompting you briefly push the gas pedal all the way down (do not over rev the engine).

So the engine needs to be revved, but don't hold the pedal down for more than say 1/2 a second?

10. After a little while the check engine light will start flashing codes at you.

What's a "little while"? I want to be prepared to get the codes, and it doesn't take much for me to lose focus.

As always suggestions are welcome, and any advice is appreciated. Thanks!

 

There's no maximum. As long as the engine is at operating temperature you're fine - doesn't matter how it got there really.

Timing light is perfect. It's also a good time to check the base timing, but you certainly don't have to. Just verify that the timing isn't stuck on a single value at idle and just above.

Doesn't matter. All the 5.0 manual transmission trucks should have one, but beyond that I'm not sure what did and didn't have a PSPS.

Correct. Just a quick stab to wide open and release.

It's almost blinking codes as soon as you release the throttle from the goose test on my truck. I'd think within 30 seconds at most.

 

Thanks Eric- I really appreciate your taking the time to answer them. Now I can be certain I'm doing things right.

 

After you get the engine ID (number of cylinders) you need to possibly do three things:

- test the PSP switch with a half-turn in each direction - I think only the 302 has a PSP switch, as it's the only motor that doesn't always produce enough torque at idle to run the power steering pump
- cycle the O/D switch (if you have one)
- step on the brake

If you don't do these it will throw a code for each one.

 

Yeah the only thing I'm not sure of is the PSP switch- the o/d switch I have so that and the brake I can do.

 

To find out, you could not turn the wheel and see if the code comes up for PSPS (52?), or just turn the wheel regardless.