2001 Chevy 1500HD engine question
 

My truck when idling has a stumble. It will run smooth then rough then smooth back and forth. Didn't do it while driving before. Now when pulling at low speeds it started doing it. When at highway speed even pulling its fine. Check engine recently came on but it's for the knock sensor. I was told that wouldn't cause the stumbling? No other codes when checked. Ideas? Thanks.

Re: 2001 Chevy 1500HD engine question
 

Water in the fuel ? ---Trevor

Re: 2001 Chevy 1500HD engine question
 

How old is the fuel filter?

Re: 2001 Chevy 1500HD engine question
 

So far new fuel pump, new filter, wires, plugs, pcv valve. No change. Bought new intake gaskets and knock sensor. Doing that next.

Re: 2001 Chevy 1500HD engine question
 

Did you try the following, clean the mass air flow sensor, clean the throttle body, check the intake manifold gaskets, is there any oily residue in the intake manifold from the crankcase vent. system, and do you use any type of injector cleaner. I use the Lucas fuel treatment with excellent results in my '95 F-150 (195k), '99 5.7 Suburban (115k), BUT Chevron Techron has worked miracles in my wife's '06 TrailBlazer SS (135k) that has had similar problems to yours.Believe me, I know full well how frustrating this stuff is. Carbs. and distributors forever!!

Re: 2001 Chevy 1500HD engine question
 

Ed, remind me next time we are both going to be at the track. I will bring my Tech2 scan tool. I should be able to tell you what it is, and which cylinder(s) are the culprits. The knock sensors won't be the problem.

Re: 2001 Chevy 1500HD engine question
 

Ok I will Ed thanks.

Re: 2001 Chevy 1500HD engine question
 

You will need harness for knock sensors also, water bad to get trapped in knock sensor holes. Jamie

Re: 2001 Chevy 1500HD engine question
 

Ever check the Idle air control? That little actuator deal is always moving back and forth to maintain your idle characteristic maybe try a new IAC.