Light Gas Pedal Clunking

spikesputnik · June 29, 2009

Every time I start the engine and drive off, I feel two light clunks through the gas pedal at about 10 mph or so. They are separated by 2-3 seconds, with the first one slightly more noticable. Sometimes I don't even notice it at all, but if I pay attention, it's always there. Not alarming in intensity, everything runs fine otherwise. Only does it after startup, not after a stop sign. No change in intensity over a couple of months.

What is this? Throttle servo calibrating? 5.3l 4spd 2wd

punmax · June 29, 2009

Don't have a clue, but I would mention it to the dealer.

gmercury · June 29, 2009

I noticed the same thing with mine, did it from day 1. It only does it when you first go. Not real bad or anything but noticable more so by feel than sound.

2005LT · June 29, 2009

I have the EXACT same thing with my 6.0L 6 speed. Right after start up on first acceleration out of the driveway. Since we have different engines and transmissions I wonder what it could be?

sleblanc63 · June 29, 2009

Mine does the exact same thing. Has done it since day one.

jrrod2004 · June 29, 2009

that could the be the trans shifting from 1-2 and then back down to 1 from 2. Mine did it when new and dealership said that under light acceleration, the truck will shift frequently (to keep better MPGs I guess)

bill190 · June 29, 2009

Newer vehicles may have a gizmo to adjust the throttle. This would probably be for traction control. If it notices a wheel starting to slip, one option for the computer is to ease up on the throttle a bit. Probably something like that.

This is the exact opposite of ABS. Keeps the tires from slipping when accelerating.

I was reading about this the other day and thinking this would ruin all the teenagers fun! No more screeching tires because the computer would notice they were about to slip and automatically ease off the throttle!

mipsco1 · June 29, 2009

not just a gm thing i think. Girlfriends 2009 escape does it. Im not sure if its TC because i dont think the ford has enough power to break free at 1/4 throttle.

spikesputnik · June 29, 2009

Just left work with the TC turned off->still does it. It feels like a light hydraulic or servo" thunck" felt through my gas pedal....like maybe the tranny and throttle servo are interacting. First thunk is firmer, but there is always a second smaller one about 2-3 seconds after the first. Not worried about it, just wondering.

C. Charles Hahn · June 30, 2009

All drivetrains have a little bit of play in them from the factory, are you guys sure this isn't just u-joints or something like that seating themselves after being at rest?

spikesputnik · July 1, 2009

All drivetrains have a little bit of play in them from the factory, are you guys sure this isn't just u-joints or something like that seating themselves after being at rest?

This is a timed, automatic, absolutely predictable happening, and is always under light load on initial drive off only. Also, I don't think that a drive line clunk would be felt through the gas pedal only. I'm starting to think that it is related to transmission coming up to pressure after a rest- something that bleeds out/releases when turned off and has to reprime?

I'm gonna pay attention and see if it happens with a hot engine today, and check it out in reverse....

jf781 · July 1, 2009

New here.... been lurking for awhile and figured I'd post make my first post (I'll get over to the introduction thread next).

Haven't noticed it on mine yet (Wife drives it more then I do), but i know on my 06 grand prix it was the ABS cycling when you first take off. Maybe your feeling it though the accelerator since your not hearing it.

Could be way off but the way it sounds (firs taking off, around 10 mph) sound like it would fit the bill for me. Just a thought.

sleblanc63 · July 1, 2009

It is not the transmission. It is a feeling like someone physically taps the bottom of the accelerator pedal. No rpm or gear change. No engine response... nothing. Just a feel through the pedal. If my pedal were physically attached to a carburetor I would say it felt like someone hitting the linkage from the side. No increase or decrease in rpm's or pedal stiffness. Just a tap back through the pedal.

spikesputnik · July 1, 2009

It is not the transmission. It is a feeling like someone physically taps the bottom of the accelerator pedal. No rpm or gear change. No engine response... nothing. Just a feel through the pedal. If my pedal were physically attached to a carburetor I would say it felt like someone hitting the linkage from the side. No increase or decrease in rpm's or pedal stiffness. Just a tap back through the pedal.

Exactly. In my mentioning the tranny, I was more alluding to the probable computerized connection between the throttle servo and tranny servos, like the throttle and tranny are discussing amongst themselves whether they are both "all systems go", and the throttle servo is double checking the pedal position, making minute adjustments, or calibrating itself?

ABS is another thought...I had an Acura once that did that ABS cycling also.

CapitalTruck · July 2, 2009

Well, I couldn't find it to save my life, but there was a bulletin about this some years back (I remember being relieved when I saw it). That is the throttle doing some sort of self diagnosis check. It should only to it once after starting. Totally normal.