idle and trans problems

big bird

Registered User
My 89 auto SC has problems holding a steady idle and sometimes stalls out when idling while in gear. I recently replaced the plugs and wires and cleaned the throttle body which helped a little, but the problem persists. I have seen many suggestions on this forum ranging from alternator, tps sensor, vacuum leaks, to motor mounts. Problem is I dont want to go bankrupt in the process. How can I verify what is causing my problem or eliminate things that aren't at fault.

Also, my auto trans, in my opinion, shifts way too early under normal driving conditions. For example, it shifts into second almost immediately once the car gets moving. Third gears comes not far behind and overdrive consistently activates at 45 mph (i'm fine with the overdrive, its the 2nd and 3rd gear shift points that are bothering me). Is this normal as it always seems that i'm driving around town in to high of a gear.
 
Does your SC have any idling difficulty when the gear selector is in neutral? If not, then perhaps it is related to the transmission. What brand and type of spark plugs are you using? Also, have you checked for vacuum leaks? This can be done without any special tools.. try spraying water around the connection points and listen for hissing. If you have any starter fluid, that will also work well, the idle will rise if you find a leak. As far as the trans, It could just be your driving style. If you are light enough on the accelerator, it could shift early. As long as it shifts correctly under WOT, it is probably ok. Check the dipstick for fluid level, correct color(pink or red), and odor(no burn smell). My knowledge of transmissions is not significant, so others may have more info on this..
 
In neutral, the idle is much better. I am using champion double platinum plugs. The transmission shifts at much higher points under hard acceleration, it is only in routine driving that the shift points seem too low. I don't believe the transmission is related to the idle problem. I will check for vaccuum leaks, but where exactly do I check? I"M ASSUMING I CHECK ALL ALONG THE AIR INTAKE HOSE ROUTING, AND IC TUBES ETC, ARE THERE ANY OTHER MAJOR VACUUM AREAS THAT NEED TO BE CHECKED THAT ARE"NT OBVIOUS TO A NOT SO GOOD BACKYARD MECHANIC LIKE MYSELF. THANKS FOR THE INPUT..
 
Multiple items can affect low idle. A vacume leak is not typically one of them. A vacume leak adds additional air and should cause irratic and increased idle speeds.

There could be an issue with the integration between the Auto Transmission and the engine idle. I believe there is a cable that handles this. Don't know, don't have an Auto.

Otherwise it could be the Idle Control Solenoid is no longer able to reach the proper range to set the idle correctly.

Any engine codes?
 
Engine light is not on and no codes are comining up when scanned. This is why i'm trying to pinpoint the most probable source of the idle problem because i just don't have the cash to let a mechanic go hog wild and start replacing one sensor after another. anyway all input is greatly appreciated. Thank you fellow sc'ers,
 
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