i have a 95 deville and the service engine soon light recently came on...i noticed that while driving when i let off the gas there is a low humming sound coming form the engine....when i am stopped the idle is very high...so high that when i shift to drive or reverse the whole car will jerk. When slowing down for a red light the car will even jerk as it downshifts....does anyone have an idea what this could be?
95 deville idle problem
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maybe the tranny needs to be looked at. A new brake job could be in order. Or go get a good tune up. Also when i was in my tempo i had a problem with hard idle and i eventually had to replace my motor mounts. That cost a little bit of money i hope it is not the motor mounts.
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Remember how a gasoline engine works, when more air is let in, fuel is let in aswell and your engine speed goes up. So you either have a vacuum leak, or an ISC motor issue, either something is telling it to stay erect, or it is stuck erect. I would check for vacuum leaks first, cause the hum could be the sound of air sneeking in and vibrating as it does. Because you say transmission harshness, and because even though GM calls this trasmission electronically controlled, it still has a vacuum modulator, how ford is that? This is a fairly large volume vacuum port, a compromise here would not only yeild a substantial vacuum leak causing high idle and hum, but trasmission malfunction as well. But if you have an MIL on, check it first, that will probably lead you to the problem.Vinnie87 said:
-The Cadillac Rancher
im willing to bet your ISC motor has gone to that great junkyard in the sky ...look into replaceing it
i recently had that same problem with my 94 sedan deville and i had to get a new idle motor put on my car because the idle motor had gone bad. If you want to temp. fix the problem to prevent your tranny from slipping, tighten up your idle motor with a wrench and it will bring the rpm down, if you have a 4.9 it should be right in front of your thottle body. That'll do untill you get it replaced, hope i helped...
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if its a notrhstar they had problems with Map sensors and ISC motors not retracting
On a 4.9 check for a vaccuum leak, and be sure your isc motor is retracting...when its idling up....take and pus the throttle close if you hear the isc click its probably stripped out on the inside. cand be a pain to replace sometimes
On a 4.9 check for a vaccuum leak, and be sure your isc motor is retracting...when its idling up....take and pus the throttle close if you hear the isc click its probably stripped out on the inside. cand be a pain to replace sometimes
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i had the same problem with my 94' last year. i called it the "run away" car. lol. It ended up being a bad Throttle position sensor. All better since i fixed it but it got so bad that i could get going about 65mph without even touching the petal!
Has your car recently been serviced ( oil change ETC...) Usually what happenes is these brainiacs at your local oil change shop will check your air filter, and in doing so, knock off your MASS airflow sensor vacume line. It is a thick vacume line located by the air filter in the housing.
My 95 Deville had gone badly like that, this problem can still exist after changing the following:
- ISC motor
- TP Sensor
- Catalytic Converter
- Muffler
- Clean the blades in the air intake
- O2 sensor,
This problem wastes a lot of Gas because the car is constantly wants to drive on it own, and also works your brakes. so it's either something is stuck like the gas pedal cable, or a vacuum leak (epoxy worn out at the base of T Body), the transmission is fine with my car, I honestly couldn't stand my caddy like that, and ended up buying new Toyota Camry for "Gas sake". I still have my Caddy and it's a beautiful car, but not too many people want to touch (repair it) it or know about it.
But it seems like after doing the tests in the shop manual, the car does go down to its book idle speed when it's parked. When I drive it and I'm going to a stop, it feels like the gas pedal is still pumping gas, then seconds later after hitting brakes, the surge dies, and comes back again when driving. if it is a vacuum leak, the engine should stay high at all times?! isn't that true?
Maybe you have a problem with the throttle cable or the throttle return spring or the throttle body bore and blade need to be cleaned thoroughly or there is something (like a floor mat) holding the accelerator in position. Do you have aftermarket floor mats? Have you made absolutely sure they aren't rubbing? If you remove the air filter box and hose and the MAF, push the throttle blade open and let go of it. Does it stick in position or snap shut quickly? Inspect the throttle cable carefully to ensure there are no nicks or cuts. Look at the cruise/throttle cable junction and make sure everything moves as it should.
I'm launching a war of TB cleaner, Gas pedal cable inspection and WD-40 on my TB and gas pedal. it seems that this problem of high RPM is getting out of hand. I just hope everybody post what solutions they found for their problems so we can benefit.
So cleaning the TB should be really detailed around the blades,,,
So cleaning the TB should be really detailed around the blades,,,
There is always the most simple of answers. The intake could be leaking. That would make it accel, That would be too easy though expecially cadillac.
i know this soudns dumb but my friends 94 concourse had the same problem. I told him to make sure that the engine wasnt overheating because that would raise the idle in an attempt to flush the system with coolant. Sure enough he added coolant and he was stylin again. Just make sure your car isnt overheating.
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