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1993 DeVille sparattic idle upon start up

7K views 14 replies 2 participants last post by  Ranger 
#1 ·
Hello everyone. It's been a while since I've posted here last; but I’m having some issues with my car lately. About 1 out of every 3 times I start my car, weather the car is hot or cold, it idles very strangely. The idle will surge between about 700 and 2000 rpm's, sometimes so radically it kills itself. The idle usually regulates itself after 10-20 seconds of run time.

Anyhow, I believe I have found the culprit. Pictured below is the solenoid I believe is causing the problem.



Every time after I shut the car off, I can hear it retracting and extending itself for about 20 seconds after the ignition is off; even if the key is removed. I know this unit makes idle adjustments while the A/C is on, but does it also control normal idle function? Have I found the problem in this solenoid, or is there a module that controls it that might be going bad?

This problem is on a 1993 Sedan Deville
 
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#3 ·
I thought so. My concern was is it the ISC motor itself going bad or is it part of the computer that controls the unit itself? Is this a common thing to go out?

I checked a few local auto parts stores today on a price for the motor and the cheapest I could find it was for about 81 dollars.

If I remove it, is there anywhere you can think of that would perform a test to see if it is malfunctioning before I shell out the $81 for a new one?
 
#4 ·
It's all one unit. You can pull the switch and clean the contacts. I forget how without looking at it, but there may be some threads about it. Failure is somewhat common after time. Be sure to find the adjustment procedure after installation. I have posted it many times.
 
#5 ·
Thank you both for this helpful info. It's been driving me nuts! I'll pull it in the morning, clean the contacts, adjust, and start from there. I should have mentioned the car just turned over 114,000 miles, so it's done its fair share of work. The solenoid appears to be original.
 
#6 ·
Ugh. Well it seems that I have more problems to worry about than just the ISC unit. I did a diagnostics check through the Climate Control Center as instructed on the forums page as my check engine light seems to come on as it wants. The results were not good.

P016 (E016) ......................................... Voltage Out of Range [ALL SOL] <----No idea

P039 (E039) ..... Torque Converter Clutch/Viscous Converter Clutch Engagement Problem <----This explains the torque converter unlocking on the highway

P065 (E065) ................................................... Cruise - SPS Failure <----The cruise works fine :hmm:

P085 (E085) ........................................... Idle Throttle Angle Too High

P091 (E091) .................. PRNDL Switch Problem (transaxle range switch problem) <----?

P096 (E096) ............................................ Torque Converter Overstress

P098 (E098) .................................... High RPM P/N to D/R Shift Under ISC <----This answers my initial question.


Oh boy :nono: :bonkers:

I take good care of this car, but I guess my best efforts are useless. I really wish I never checked them. This is just depressing.
 
#7 ·
P016 (E016) ......................................... Voltage Out of Range
If this is a battery voltage DTC and you drop the voltage real low, it will set all sorts of false codes. Make sure your battery voltage is good, clear the codes and see what returns. Take note as to whether they are current or history.
 
#8 ·
Thank you. Well I do have some good news. I took the ISC motor off, took it apart and oiled all the gears and sprockets inside and reinstalled it. No more crazy idle!

Next on the list is to give the battery a nice long charge and remove and clean the EGR valve.

Eventually I want to drop the trans pan and change the filter. Then, take the car somewhere to have the transmission flushed and maybe nip some of the transmission problems in the butt.


Its time to take action and chase these problems down rather than cry about them!
 
#10 ·
Thank you Ranger. I adjusted the ISC motor back to the way it was when it came off. I will also be sure to read up on transmission flushing as you suggested.

If I may ask, what is the difference between a check engine light and a service vehicle light? I think I know where the cruse control malfunction code came from:

This past weekend, I took the car on a 200 and some mile trip. I was on the highway when the service vehicle light came on. At this point, I had not used the cruse at all that day. I then (by chance) tried to engage cruse control while the service vehicle light was lit and the cruse wouldn't engage.

Once the light went off after about 5 minutes of being lit, I was able to engage the cruse. I'm thinking the computer stored the trouble code, because after the light went off it worked properly all the way home.
 
#13 ·
If you really want to drain the torque converter as well, then pull the supply line to the side tank and add a hose and put it in a bucket. Start the engine and let it idle and pump the trans down. Shut it down when it stops pumping. Then drop the (dry) pan (no mess).
 
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