Hi,
My 89 Sable is running great exept for this; sometimes after driving at highway speed for 20 miles or so I finally come to a light and the idel is racing up to 2500 rpm's. If I keep driving it wil keep racing, I have to turn the car off for a minute and then restart, then it will work normal again. It never does this driving around town at 35 mph speeds....

puzzled,
Jeff

 

there may be some binding in the throttle cable or the cruise control cable may be out of adjustment. There may also be build-up in the throttle body preventing the flapper from closing fully. If it's carbureted, then it may need some tweeking of the throttle linkage or fast idle setting.

 

Thanks for those ideas to check out. It happens very rarely but like I said the formula is highway speed for a long duration like 25 miles, then when you come to a stop light, the idle is racing, nothing kicks it down but restarting it.

I will check the linkage, carberator and cruise control, because I was using the cruise control and forgot to mention that. Could it be in the direction of electronics with a sensor or computer decision because restarting solves the problem?.

Ok, thanks, I welcome all suggestions

 

it could be a flaky throttle position sensor. Since it is carbureted, you may need to check the choke. The choke may be holding the throttle open at the fast idle setting. This could be caused by a bad choke coil, the connector falling off the choke, or just getting turned out of adjustment.

 

ooooops.............this Sable is fuel injected, just was thinking it's old 1989 and didn't check on the carburator, but it is fuel injected. So, will I still need to check the choke/fast idle setting? The throttle sensor sounds like the problem but there is no check engine light, , ,maybe I could just replace the sensor, the car is 20 years old, wow!!

Thanks again ~

 

with fuel injection, sometimes a TPS won't throw a code if it's just not resetting properly. that could be it. The fast idle is controlled by the computer and coolant temp sensor. If the engine is not up to temp (very cold temps on the highway could cause the temp of the engine to drop back down if the thermostat is stuck open or missing). Check your coolant levels too. If it's low, it could cause false low/high readings. You should definitely check the throttle body (where the hose connects to the engine from the air-filter box) for carbon build up as this can hold the throttle open. You may also need to clean out the idle air control that's attached to the throttle body. This controls the idle speed on fuel injected cars. Considering how old the car is, I'd rather think the buildup is the issue before the electronics. You may also need to check and clean wire harnesses that go to these parts.

 

Thanks again, I think you've got the solution. My sister had the same problem with a Ford Escort, old, and my brother in law who is a mechanic replaced the TPS and cleaned the carburator and it worked fine after that. On my car since turning off the engine and restarting it solves the problem wouldn't that point to a computer/electronic sensor issue?

Either way, we are going to clean all the linkage connections & carbon build up and just replace the TPS, he can do it so I won't even have a shop fee. Since it doesn't happen all the time, I can't just test it immediately, the only way I'll know it is fixed is if it never happens again......

J

 

turning the engine off also resets the idle air control motor if I remember correctly. But yes, it does lean towards the electrical/sensor issue. cleaning out the intake like you're planning on doing is also a really good thing to do just because it helps things work better and air flow smoother (which in turn may help get a little better gas mileage)