Vibrating pedal with brief power loss

[chrischris]

Hi everyone,

My 1981 pickup has recently been acting strangely. Earlier this week I noticed the accelerator pedal was vibrating while driving, to the point where my foot started to almost go numb. The vibration continues even when the engine is warmed up.

Also, I have noticed that whenever I shift gears (mostly noticeable going from first to second) there is a very brief power loss, causing a quick jolt in momentum. This jolt seems to occur at the same rpm range. At freeway speeds, I must be at this rpm range because I swear I can feel the power surging a bit, nearly making me nauseous.

Everything under the hood looks mechanically sound, but I can't figure out for the life of me what is causing the brief surge in power and pedal vibration. Any help would be appreciated.

Thanks.

[coke]

Check all the injection pump mounting bolts to ensure they are tight, or in some cases, even exist. There are 4. 3 on the front, 1 on the bottom rear.

Make sure the brackets the pump mount to are tight as well. There are two. One that the front mounts to, and one that rear bolts to.

[82vdub]

I'm with Coke here. The gas pedal is a cable, so it's not a rigid connection to under the hood. I believe that the only thing that could be happening is that your IP is moving, or the motor itself. How good are your motor mounts?

[bscutt]

My 1980 Rabbit did this and I found that just tying down the cable itself at a few points kept the vibration from traveling to the pedal. Sometimes you can get standing waves induced into the cable at certain engine speeds and it gets to oscillating (like that bridge in Tacoma in 1939...)

[Vincent Waldon]

Check the 4th mounting bolt on your IP carefully... the one down low at the high-pressure end. It likes to wiggle loose and then the pump passes on the fact that it's now dancing the rumba directly to your right foot. BTDT.

[Fatmobile]

Yes, and the surging or change in power can be another symtom of a loose injection pump bolt/nut.

[coke]

Maybe Volkswagen will hire all 3 of us due to our extensive knowledge, huh?

[tylernt]

I had the same symptom -- vibrating accelerator -- until one day I had no accelerator. Turns out the hook in the pedal end of the accelerator cable goes through a rubber bushing -- a bushing that falls apart over time. When this happens, engine vibration is transmitted directly to the pedal, and in some cases the hook unhooks itself from the pedal.

If the bushing goes, you'll also lose the last 1/4" or so of throttle, leading to an apparent power loss and sloppiness/jerkiness in throttle changes.

[vwkook]

anyone have a part # for that bushing or something else that would work? Mine's probably been gone for three years or so now.

[tylernt]

A Google search turned up 431-721-559. No promises that's accurate though!

Jack, the owner of this site, could probably hook you up with one.