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Tim West
Tim West, ASE Certified Technician
Category: Ford
Satisfied Customers: 4638
Experience:  ASE Certified Service manager of Firestone
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I have a f250 heavy duty. 1997. 460 , auto trans.

Customer Question

I have a f250 heavy duty. 1997. 460 , auto trans. At more than half throttle it stalls and is sluggish starting from a stand still. At highway speeds, if I give it enough throttle to downshift, the rpms get over 3000 and the the engine stutters and the rps go up and down erratically. Other than being sluggish from starting stopped it runs fine below 3000 rpms. Any ideas?
Submitted: 7 years ago.
Category: Ford
Expert:  Tim West replied 7 years ago.
Thanks for visiting Just Answer,
Is there a check engine light on?
Customer: replied 7 years ago.
No. All of the lights cycle as they are supposed to when I start the truck, but nothing else comes on after that. I am changing the fuel filter in an hour. Not sure when or if it has been changed before. I just purchased the truck. Another thing was yesterday. The AC works great, but if you start the truck with the AC turned on, it will not idle correctly. It tries to die until I turn off the AC. Then it idles fine and I can turn the AC back on. Not sure if these are related issues.
Expert:  Tim West replied 7 years ago.
This could actually be a problem with the PCM.
Perform the KOER (key on engine running) self test. Check for incorrect idle hardstop. The engine should idle between 550-600 rpm on a hot engine with the IAC valve unplugged. Reset the idle strategy by disconnecting the battery for about 15 minutes. Verify that the PCM (Powertrain Control Module) has battery voltage to pin 10 whenever thea/c clutch is engaged.

If not, there could be a PCM issue.
graphic
Customer: replied 7 years ago.
It has an auto trans and is idling at about 850 rpm with engine hot. How do I perform the KOER?
Expert:  Tim West replied 7 years ago.
Oh, just unplug the iac and verify idle drops to 550-600. Do this when the engine is warm.
Customer: replied 7 years ago.

Yes. When the iac is unplugged, idle drops to 550

 

Expert:  Tim West replied 7 years ago.
That sounds right then, check for about 10v at the wire at pin 10 when the a/c clutch is operative.
Customer: replied 7 years ago.

Where is the plug located that i need to test? I cant find anything thats refered to as a pcm in my manual.

 

 

Expert:  Tim West replied 7 years ago.


The Powertrain Control Module is located at the LH side of the safety wall.

 



 

Customer: replied 7 years ago.
ok. I have 11 volts at pin 10 when the ac is turned on.
Expert:  Tim West replied 7 years ago.
Okay, that is no problem there thanks for checking that,
Have you tried cleaning the mass air flow sensor?
Customer: replied 7 years ago.

No. I read that cleaning it could damage it.

 

Customer: replied 7 years ago.
It has a throttle position sensor. Cant find a mass airflow sensor. Do they have both?
Expert:  Tim West replied 7 years ago.
the MAF is located in the hose coming from the air filter box.
Try wiping it clean with a cloth,.