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When the truck is running, do you have a Service Engine Soon light?
Service Engine Soon light on, I mean
No engine light on
that is what I thought
You most likely have a problem with the MAF sensor.
90% of the time the MAF ( Mass Air Flow ) sensor heated element which meters the air so the computer can add the proper fuel mixture has fallen out of spec. Not enough to cause a Service Engine Soon light but enough to cause the Air and fuel Mixture to be so off it can cause Stalling, poor acceleration, won't rev over a certain Rpm, and running issues. I would have the Air and Fuel mixture readings checked to verify. Checking the voltage will not show the fault, the air and fuel mixture will. If found to be bad, do not replace with a After Market one. After market MAF sensors never seem to work properly. There heated element doesn't work right which can cause 02 sensors to flat line and have you chasing you tail trying to figure out what is wrong. So the only way to correct this issue if you do have a bad MAF sensor is to replace it with a OEM.
If you have any more questions on this, please feel free to ask. Thanks Jay!
Thanks Jay, I'll give that a try. I was tempted to replace the plugs, cap and rotor, but the engine shows no signs of misfire. The car does have 176K miles, so something of this caliber was due.
Changing the plugs if you haven't done it wouldn't hurt. But if you had a misfire issue, normally it would throw a code. If you had a code, I would think you had more of a distributor problem
The MAF does sound as if it is the culprit, that may expalin the poor fuel economy too.