if Im ideling and the heater is on then the engine revs like from 500-700 up and down...if i shut it off then the surging stops...is this normal.....114,000 miles and still tickin

 

anyone?

 

Do you have a lot of electrical accessories on your truck?

 

Pop the hood and see if your A/C is kicking in. The system might be calling for "defrost" when in heat, or an electrical issue could be making it run. The A/C sucks quite a bit of power and can make your RPMs drift.

 

when you are turning your heater on, are you also using defrost? The defroster will cause the A/C compressor to kick on, engaging the aux. fan as well. The PCM will therefore boost idle to assure you will not stall...

 

Any position to the right of the floor symbol will activate the a/c compressor.

 

It sounds electrical. When I first hooked up my e-fan I had it running on the high speed motor and when I would run the fan, my heater blower, head lights and fog lights all at the same time I would get a little surge like you are describing.