Fast Idle

It was another one of those situations where I should have learned my lesson - women KNOW what they are talking about!! Listen to them!!

It was my daughter again. This time she was telling me about her problems with the car wanting to run away all by itself. Sounded at first like my uncle Matt's Studebaker but this was different. She complained that she could pull up to a light and the brakes seemed like they weren't going to stop the car, an '85 Olds Cutlass Cierra with a 3.0 carbureted six in it.

I took it for a test drive and stopped at the Rundell Library to pick up the service manual. When I pulled into the library parking area I almost rammed the car in front of me - it seemed like the brakes weren't working. I slipped it into neutral and it raced like the throttle linkage was stuck. I gave it a ceremonial tap on the throttle to see if it was stuck on the hi-idle cam of the carb, but no luck. It just sat there and raced. She was right.

I checked out the service manual and headed home. I stopped at my buddy's house and picked up the gizmo* that lets me tap into the computer interface just in case. Back in the Lazy Boy I read all about the idle control mechanism. Olds decided to use a small "servo" motor to drive a pin back and forth to adjust the idle speed and to allow the throttle to close completely when the key is turned off, an "anti-dieseling" feature.

I went outside to the garage and hooked up the gizmo and started it up - it behaved flawlessly! Took it for a ride - now this is an experience you shouldn't try at home, er in your car. Always have someone else drive if you want to observe the computer readout! It's fascinating to watch the readout of every sensor in the engine output directly to the screen - in real time!.

I decided to return home after running up on the neighbor's lawn and asked Arleen to drive while I played computer guru. I watched as the shift switches opened and closed and watched the mixture control toggle back and forth from rich to lean. The engine temperature display showed the engine warming up degree by degree. Everything was working just fine. Then it happened. Arleen pulled up to a light and started complaining that the brakes weren't working right and she might have to run the light. I reached over and popped the transmission into neutral. Then I saw it. The readout for the "throttle closed" told me that the throttle was open, yet Arleen's foot was off the gas. I popped the hood and slipped the air cleaner off. The throttle linkage was free, however I noticed that the servo motor had pushed the idle pin well up into the fast idle position. I tapped the servo with a small wrench and immediately the idle pin retracted and the Olds came down to a normal idle speed.

Back to the Lazy Boy to read some more about where the "throttle closed" sensor was. I found that it was inside the servo motor and that it was spring loaded so that it popped open as soon as the throttle was pressed. The servo immediately drives the idle pin out. If you then release the throttle abruptly, the switch closes (or at least it should) and reverses the motor to slowly let the throttle come back to the idle position. This is the function that the dash-pot (a pneumatic shock absorber of sorts) did on the older cars.

I removed the servo motor and took it to the workshop. Now you can't tell me that there are no user serviceable parts inside anything so I pried and pulled and tugged and finally the servo motor came apart to reveal a very dirty and corroded set of contacts which acted as the "throttle open/throttle closed" sensor! A quick spin of the Dremel tool and the contacts once again shone brightly. I sealed it up with a small amount of RTV and re-installed it.

It performed flawlessly for at least twenty five stop-an-go events and I turned it over to my daughter who drove it for another two years with nary a hint of the problem ever occurring again!

*The gizmo is a commercially available computer analysis tool which I sell from my website. It is called the Diacom unit. Send me a mailnote if you are interested in buying one.

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