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1993 Cadillac Sedan DeVille, 1995 Sedan DeVille 4.9 V8
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40 Posts
Discussion Starter #1
I don't know if I'm willing to deal with this problem any longer. The car has had an idle problem since January of this year. Replaced O2 sensor, ISC Sensor, TPS sensor,Dealer cleaned the TB, replaced fuel filter. Car idles fine for 15-20 seconds and then starts dropping and surging.
 

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1993 Cadillac Sedan DeVille, 1995 Sedan DeVille 4.9 V8
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40 Posts
Discussion Starter #3
Yep. Car never threw a code except for one. E55(just had the dealership replace the TPS)
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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567 Posts
Similar issue with my Fleetwood (although not identical.) The list of things it couldn't be might actually be shorter than the list of things it could be. If you have no codes, it's time to start testing... well, everything. You have the same choice I did - do the proper diagnostic work, have it done by someone else, or load a shotgun with parts and money, and fire it at your car until something corrects the problem.

If the problem is only when idling, it might be time to clean/replace your ISC motor. You can search this site and find more info about that process. If you have the factory service manual, you might be able to get more info from your car using it's directions, even without a Check Engine Light or codes setting.

My car was/is acting up at idle, on coasting, and occasionally when accelerating. I replaced a bunch of ignition parts and all the filters, and there was no change. I figured having new ignition parts was worth the money though, so no big loss. Further diagnostics have lead me to a failed injector. So you either have to do the work, or hope you're lucky and roll the dice. I hope you have better luck than I did!
 

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1992 DeVille
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2,339 Posts
Hows the fuel pressure?

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Yeah man like eat said it definitely could be an injector possibly.

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When did you last do cap coil rotor plugs wires tune?
 

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1993 Cadillac Sedan DeVille, 1995 Sedan DeVille 4.9 V8
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40 Posts
Discussion Starter #6
I think I've thrown at least 500 bucks at it already. But yeah, it's driving me insane because I can't figure out what it is. I've replaced most of the stuff and next up on the list is the fuel pressure regulator or test for a bad injector.

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Also I took it to an independent shop and had the 30,000 mile service done. Replaced spark plugs and wires, flush transmission and coolant, oil change, multi point inspection. At this point I'm pretty much ready to throw parts at it again, but I can't figure out why there isn't any codes.

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Never thought a car with 52,000 miles could have so many little problems.
 

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1993 Cadillac Sedan DeVille, 1995 Sedan DeVille 4.9 V8
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40 Posts
Discussion Starter #8
The car is going back to the shop soon to see if it can be corrected again. And as far as I know, there isn't any vacuum leaks, the car works perfectly apart from the idle. I'm leaning towards a temp related issue though. Is it a minor coincidence that the engine temp lights don't function anymore?
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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567 Posts
I don't know on your car, but on some GM vehicles, the coolant temperature sensor is also the temp sender. If the coolant temperature sensor doesn't work correctly, it will affect how the car runs - but I think it would be more consistent, not just at idle but all the time.

I'd still think getting your Idle Speed Motor checked out and/or cleaned should be considered. Trouble only at idle, and a part that controls idle... warrants consideration.
 

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1993 Cadillac Sedan DeVille, 1995 Sedan DeVille 4.9 V8
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40 Posts
Discussion Starter #10
I do believe I did replace the ISC. Somehow ended up with a high idle, so I replaced the TPS and now I'm back at square one. At least it doesn't stall like it did before I replaced everything.
 

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White Diamond '03 DHS (with DTS floor shift)
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86,783 Posts
Did you adjust the ISC motor plunger after installing it? There is a special procedure.
 

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1993 Cadillac Sedan DeVille, 1995 Sedan DeVille 4.9 V8
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40 Posts
Discussion Starter #12
I had the mechanic install and adjust the new unit. The car battery died a few minutes ago, I'm currently trying to do the car computer reprogramming procedure.
 

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1992 DeVille
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2,339 Posts
Mattgentry said:
I had the mechanic install and adjust the new unit. The car battery died a few minutes ago, I'm currently trying to do the car computer reprogramming procedure.
there's a thread on this forum that I posted the 91-93 fsm procedure to calibrate the entire system. Starting with verifying timing, min air screw adjust/verification, tps setting, isc plunger gapping. All needs to be done with a clean tb.

These efi cars will nickel and dime you to death if you let them. It's always best to properly diagnose and go from there.

I like rangers idea of checking for vac leaks. What's your vac reading at idle and what's your fuel pressure like??
 

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1993 Cadillac Sedan DeVille, 1995 Sedan DeVille 4.9 V8
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Discussion Starter #14
Oh dear lord this car is going to kill my pockets. Anyway, I have no idea about the vaccum or how to test it, however the mechanic tested the fuel pressure and told me everything was a-ok there. And thanks, I actually had no idea there was a special procedure until you all mentioned it. I don't know what I would do without these forums.
 

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1992 DeVille
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2,339 Posts
Mattgentry said:
Oh dear lord this car is going to kill my pockets. Anyway, I have no idea about the vaccum or how to test it, however the mechanic tested the fuel pressure and told me everything was a-ok there. And thanks, I actually had no idea there was a special procedure until you all mentioned it. I don't know what I would do without these forums.
we got you =) no worries!

I'll try to find and post the link.

Vacuum pressure can be tested by inserting a t into a constant vacuum port off the throttle body. I like to use the egr valve solenoid.

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baddaboom-

http://www.cadillacforums.com/forums/cadillac-deville-1985-2005-including-1985/620194-1992-deville-almost-dies-right-after-4.html
 

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1993 Cadillac Sedan DeVille, 1995 Sedan DeVille 4.9 V8
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40 Posts
Discussion Starter #16
Alright. I've got my chiltons manual and tomorrow I'm going to go hunting for the vacuum lines and test the vacuum. I've got a sneaking suspicion it's either that or the fuel pressure regulator.
 

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White Diamond '03 DHS (with DTS floor shift)
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Use the Chiltons as a door stop or to sop up fluid spills.

To check for vacuum leaks, just spray Brakleen, TB cleaner or any other such volatile fluid around any potential leak point (hose connections, TB base, manifold gaskets, etc.). If the RPM increases, you found your leak.
 

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1992 DeVille
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2,339 Posts
Ranger said:
Use the Chiltons as a door stop or to sop up fluid spills. To check for vacuum leaks, just spray Brakleen, TB cleaner or any other such volatile fluid around any potential leak point (hose connections, TB base, manifold gaskets, etc.). If the RPM increases, you found your leak.
yeah this. And you can create a vac leak and spray on it to confirm the rpm raise. That way you know what to listen for
 
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