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1999 Cadillac DeVille D`Elegance
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58 Posts
Discussion Starter #1 (Edited)
When I first start my car, it starts idling high and out of control for a good minute to three minutes. I can put it in drive and it will do 20 MPH by itself. I try to, I guess "flush" the engine, by pushing the pedal all the way to the floor for a split second and see if that helps, but it doesn't. It eventually stops the idling problem but the Service Engine Light comes on randomly and when I drive, the acceleration is mighty jumpy, and not a smooth increase in speed anymore. What's the first thing I should check?

I have a 1990 Cadillac Sedan DeVille.

Here's my engine: (I know it doesn't really help, but hey. :eek: )


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Random Pictures Of My Cadillac: (Click To Enlarge)


 

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1988 Coupe Deville, 1991 Coupe Deville, 1989, 1994 Eldorado
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160 Posts
check if there are any codes..
sounds like your idle speed control motor might be stuck..
 

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1999 Cadillac DeVille D`Elegance
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58 Posts
Discussion Starter #3
Is that when you go to Auto Zone and have them do the check when your service engine light is on? If so, the light stays on randomly, and more less than often. So it'd be hard to catch it at the right time as they don't do the check unless the light is on. And the high idle is only when I start the car, it eventually dies down and seems to run fine until the next start-up... the only problem while driving is the jitteryness... for example instead of a smooth acceleration getting up to highway speed, it's a bumpy acceleration as if I was tapping the pedal every couple seconds. It kind of drags when trying to accelerate until I get to a steady speed. Hm.
 

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1991 Cadillac Brougham D'Elegance 5.7 Litre, 1994 DeVille
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6,796 Posts
It doesn't matter if the light is on or not. If something made it turn on it will still keep the code even if it goes off again. You don't need to go anywhere to get it checked you can do it yourself. There are posts here that say how.
 

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1999 Cadillac DeVille D`Elegance
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58 Posts
Discussion Starter #5
I got:

E30 - ISC RPM Out Of Range
E52 - PCM Memory Reset
E66 - Cruise - Engine RPM Set Too High

Can someone help me define these and find what to look for and fix? Thanks so much for the help you've already given!
 

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1999 Cadillac DeVille D`Elegance
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58 Posts
Discussion Starter #6
Well, I took off the hose to the MAP sensor and let it shut my car off to reset it, and then plugged it back in... car drives fine now, but feels like it's going back to how it drove just 45 minutes ago. I also reset the codes to see which ones come back. I'm just a newbie trying to learn the Cadillac. I still want to know what the fixes are for the 3 codes I did have though. Buy a new part? Adjust something? I've been reading and reading but can't find it. So if anyone still can explain the codes I had, let me know. I'm checking back every hour. lol :halo:
 

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2003 STS w/BoseNav, 1993 Deville, 1985 Deville
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1,089 Posts
I had a similar problem with my 85 Deville. It would go 60MPH by itself. I commanded the PCM to do a total diagnostic (exercises all the switches, etc) and it found that the TPS was bad. I replaced it and it behaved fine since.

$50.
 

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1999 Cadillac DeVille D`Elegance
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58 Posts
Discussion Starter #8
Well, I reset the codes and got a new engine light, and the only code on now is the:

E30 - ISC RPM Out Of Range

My dad says it's the MAP sensor going bad, so I'm going to buy a new MAP sensor and hope that fixes it. If it doesn't, I'll update ya. (Unless someone here says it's something different. :hmm: )
 

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1993 Eldo 4.9 66K miles
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368 Posts
Before you do anything else, remove the air horn and clean the throttle body bore and plates with carb cleaner and a toothbrush. Reassemble. Disconnect negative battery terminal and count to 30. Reconnect and start car. What do you have now?
 

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1999 Cadillac DeVille D`Elegance
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58 Posts
Discussion Starter #10
Will try it ASAP after work around 5pm CST and let you know. Thanks!
 

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1968 Cadillac Sedan deVille, 1994 Chevrolet G20
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2,795 Posts
FWIW, ISC failure is pretty common on these cars, and yours shows much of the symptoms associated with it. I'd make sure the TPS is set correctly, then start looking to the ISC.

If it turns out it is the ISC, you can temporarily "fix" it by unplugging it, then turning the plunger screw in until an acceptable idle is reached. (this is assuming the motor inside is seized.) If the motor still moves, but moves too slow to be of any use, Hold the car at a fast idle with your thumb pushing in on the plunger. Wait until it retracts, then let up on the throttle trying to allow it to touch the ISC. let the ISC extend until a desirable idle is reached, then unplug it. Keep in mind you may have some stalling on sharp deceleration with this temporary "fix", but you shouldnt throw any codes. Try to get a new ISC as soon as you can.
 

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1999 Cadillac DeVille D`Elegance
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58 Posts
Discussion Starter #12
Thanks I'll try that after work as well. Appreciate all the advice! Now my work day is going so slow because I'm eager to get this back into mint running condition as it was before. =P hehe :)
 
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