So about 2 weeks ago I replaced my alternator.
Since then it seems when Im driving, not accelerating but just giving it enough gas to maintain speed like 30mph in town or slower. It will rev up and down, only about 100 rpms. Barely see on the tac, but can hear it thourgh exhaust note changing. Can't say it does it all the time but most of the time.

No CEL, no codes. had to remove 2 hoses, when replacing alt. But I checked them with unlit propane torch for vac leaks nothing.

Any idea?

 

It might just be the adaptive learning process after the battery was disconnected.

Other than the RPM fluxuation, does it drive ok?

 

are you running your defrost?
It may be cycling the a/c pump, which with a weak battery will drop the rpms just enough to notice it each time it cycles. Which is consistent every few seconds

 

I've put on about 400 miles since then. Drives fine otherwise. Battery is less then 6 months old and tested good.

I actually never disconnected the battery, mistake on my part (dumb i know).

 

The driveability should be smooth even with the A/C pump in operation because the IAC is very fast to account for the engine RPM change by opening/modulating air a further amount.
How this happens is the A/C has a signal lead to the PCM telling it there is an extra load and to account for it.
The Crank sensor sends a tach signal back to the PCM telling it to do a compare with an altered idle /low speed table for corrections to the IAC.
I would rather feel your seeing a light missfire condition for some reason.
Be sure the # 1 coil and injector plugs are seated in that area.
If you had to loosen the air intake hardware be sure it's back on fully.
Good luck.

 

just drove the truck to work and I'm thinking this might be it. Was more noticeable with defrost on. I'll retest the battery.

Anyone think it's possible i somewhat shorted out a wire.

 

It would not hurt to go get your battery load tested and clean the IAC.

 

Cleaned the IAC last week didn't seem to help. I'll get the battery tested tomorrow

 

tested the battery and show perfect condition.

going to take off intake tube and reinstall to make sure all is snug.