Rough idle in drive but only when sitting at a stoplight

[vt_maverick]

So having a bit of a problem that has me concerned. When I'm sitting at a stop sign or light with the transmission in Drive and my foot on the brake, I get a vibration/growling noise about a second after I come to a stop. The noise is constant until I left off the brake, then it goes right away (I don't even have to accelerate). I don't experience this issue anytime else, not while in Park, Neutral, accelerating, decelerating, shifting between gears, etc. I've done a good amount of digging and it seems like all the related threads dealt with issues experienced in those situations. Does anyone have an idea what might be going on? The vibration is very pronounced and can be clearly felt through the brake pedal, bad enough that I usually shift into Park or Neutral at lights just to avoid the aggravation.

Thoughts? Thanks!

[tom4bren]

My first thought would be vacuum leak on the brake booster.

I don't know nuthin 'bout brakes though - I just pulled that one out my arse.

Have you tried to stop a little early, let off the brake & creep forward a little then stop again to see if it still does it.

[vt_maverick]

Yep, I've done that a few times hoping it will "reset" whatever the problem is. Unfortunately that does not work, it happens every time I come to a complete stop with my foot on the brake.

[tom4bren]

Try pulling the ABS fuse to see if it goes away - just trying to eliminate variables.

[etlsport]

also turn off your climate control.. mine behaves exactly like this any time the AC is switched on (heating or cooling), whether the compressor is on or not.

i was actually just starting to wonder about the brake booster after reading your post the first time (couldnt respond from work) so thats my next step to curing the problem.

[vt_maverick]

Already tried turning off the AC with no love, but I'll give it another go on the way home today. Tom I'll give the ABS fuse a try too. Is it in the fuse panel on the left side of the dash, or under the box in the engine bay?

[tom4bren]

Sorry, Ida know

[Bob Barker]

Sounds like a simple vibration from a bolt or nut that occurs at a certain engine RPM. My wife's car does it all the time, and the SVO does it, my old Mach used to do it... Just gotta dig around until you can find the source. I could be way off, but it's the free-est thing to try that may get rid of the noise.

Does it make the noise when the engine is still in it's "warming up" phase, like early morning at the first stop you make, or is it after you have been driving a while and the engine is warmed and set at it's normal RPM while in gear at a stop?

[Bob Barker]

and I'm pretty sure the ABS fuse is under the hood. I think I remember seeing it there.

If it were break booster, I imagine the vibration would get worse if you were to press harder on the brake pedal after you stop. If you are stopped, and the vibration starts, push way down on the brake pedal and see if the vibration gets worse/better/stops/kills the truck. Something will change if it's a vacuum issue with the breaks.

[vt_maverick]

Happens from the moment I start her up until I get wherever I'm going. Seems to be something driven by the "tug of war" between the drivetrain and brake system.

[vt_maverick]

...push way down on the brake pedal and see if the vibration gets worse/better/stops/kills the truck.

That's not exactly comforting Bob.

[Bob Barker]

Maybe have someone hold the brake pedal down in the drive way while you listen around under the hood or chassis or wherever the source of noise is.

[Bob Barker]

That's not exactly comforting Bob.

It's not the worse if that happens. It will tell you what the issue is! If the truck kills then it's safe to assume that you used all the available vacuum in the system to press the brake pedal to max, and since it was leaking, you used more than the truck was producing.

[Mile High VX]

Maybe have someone hold the brake pedal down in the drive way while you listen around under the hood or chassis or wherever the source of noise is.

Make sure that they like you if you choose this option...

[etlsport]

Mine will not cure right away when I turn off the ac but like earlier today I stopped at a light and had an awful idle. Switched off the ac and nothing happened. I idled forward when the light changed but still missed the light. When I stopped it was idling perfect