A chatterbox gas pedal...

Dear Car Talk

Dear Car Talk | Aug 01, 1991

Dear Tom and Ray:

I have a 1977 Toyota Corolla lift-back with 107,000 miles on it. It has been the best car we've ever had, with a minimum of maintenance and down time. I don't want to get rid of it, but it is making a horrible noise, and no one can tell me what's causing it. It started last winter and did not do it all spring and summer, but when fall came and I started using the heater again, the noise returned. When the heater lever is all the way over to either cold or hot, it is quiet. But when I try to get just a little heat by putting the lever in the middle, something moans and groans and chatters. You can feel the chattering in the gas pedal. If I push the heat lever all the way to one side or the other, it stops. Do you know what would cause this? And can it be fixed?

RAY: Interesting question, Mickey. And believe it or not, I think we have an interesting answer for you.

TOM: You know that cars in Japan have the steering wheel on the right side, right? Well, when the American version of this car was produced, they moved the steering wheel to the left side, but they didn't move the carburetor. The carburetor is still on the right side, in front of where the gas pedal USED to be.

RAY: So to connect the accelerator pedal to the carburetor, the American Corolla required something called throttle linkage--that's a metal rod that runs across the back of the firewall and connects the two.

TOM: The result is that on the American version, the throttle linkage and the heater controls are right next to each other. And what I think you're hearing is the heater control valve interfering with the throttle linkage. That would explain why you also feel the vibration in the gas pedal.

RAY: My guess is that the control valve has worked itself loose and is no longer firmly attached to the firewall. When you move the heat lever, you push the entire valve away from the wall and make it touch the linkage. But if the throttle linkage ever got stuck, the noise would be the least of your problems. So get it looked at right away, Mickey.

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