My truck runs great at start up and warmed up but after driving for about a hour it starts to idle ruff like almost misfiring any idea what the problem could be

 

Check engine light ever come on? With that explanation it could be almost anything.

EGR valve could be sticking open which of course causes a terrible idle but is not noticable otherwise.

I mean it could be the distributor too, pickup module, cracked reluctor wheel on the shaft ( pop the cap and take a look at the wheel that triggers the module) etc.

 

No check engine light it just started doing that

 

Or fuel pressure, coolant temp sensor going stupid, bad engine ground, you name it. Start checking away and see what you find.

 

Ok thanks

 

Is this truck stock, or modded? Post up your mod list if it is.

 

Flowmasters, stage 1 chip that's it

 

ECT sensors fail frequently & make the run extremely rich. Happens without setting any codes. But it's easy to verify with a scantool, just look at the ECT sensor reading, and see if it's correct. If the sensor is telling the PCM that it's -40*F, it's gonna run like ****.

Another big cause of a rough running truck would be a worn out cap & rotor, and spark plugs. They should be replaced every 30K miles, and seem to get ignored all the time. Also, look for a bad coil wire, or a corroded post on the coil tower. Also check the reluctor on the distributor shaft for cracks, and see if it's loose on the distributor shaft. Lastly, check and set the ignition timing, and take a look at the fuel injector spray pattern.

That covers about 90% of what goes wrong.

 

Thanks ak I changed the plugs and wires like 1000 miles ago but not the cap and rotor im gonna try there first