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Thu Jun 13, 2019 6:55 am

Vanagon folk,

I have been experiencing a strange acceleration behavior in my 1986 Tin Top 2.1L Manual for some time now. The best way to describe this behavior is that the acceleration feels binary. When I step on the gas, it feels like a mild jerk, and when I step off the gas, it will jerk again and then engine brake (or coast). I want to say the threshold is right before the accelerator pedal is completely released. If I release the gas at a certain speed in either 2nd or 3rd gear, the van will rock forward and back until I disengage the clutch.

I want to say it has something to do with the Throttle Position Switch (TPS) in my GoWesty Throttle Body (new aluminum one, not rebuilt). I readjusted the TPS per the Bently and confirmed the switch is functioning correctly. I also went though my entire fuel injection system over the past year adjusting all the basics and replacing questionable parts. This helped the van run a lot better, but never solved this jerking behavior.

Is there a chance the TPS is causing this strange behavior? Or am I overthinking this and its completely normal?

Thu Jun 13, 2019 8:49 am

perhaps your throttle linkage from the pedal to the cable below is binding slightly. creating a notchy release of the cable interacting with engine operation

Thu Jun 13, 2019 9:04 am

does your shift lever move during this binary action? you may have a broken front transmission mount. look at the rubber center of it, you should see the bond to the outer steel circle on all 3 legs of the rubber, if any have pulled away from the steel, it is bad.

Thu Jun 13, 2019 9:11 am

danfromsyr wrote: perhaps your throttle linkage from the pedal to the cable below is binding slightly. creating a notchy release of the cable interacting with engine operation

+1. I've experienced this.

Thu Jun 13, 2019 9:54 am

That is a good point, I have not checked my throttle cable yet. That should be easy enough to inspect just by watching the throttle body while a friend presses the pedal.

I have cleaned the Idle Control Valve (and replaced the Idle Control Module with a rebuilt one) recently. My understanding is this valve is taken out of the loop once the car warms up?

Thu Jun 13, 2019 9:57 am

DanHoug wrote: does your shift lever move during this binary action? you may have a broken front transmission mount. look at the rubber center of it, you should see the bond to the outer steel circle on all 3 legs of the rubber, if any have pulled away from the steel, it is bad.

I recently replaced my Transaxle bushing with a Powerflex polyurethane one. I also just finished rebuilding the shift linkage including all new bushings and adjustments. I would say the shifter vibrates a bit but only because of the engine running and not due to the accelerator pedal starting/stopping.