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1990 cadillac deville
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Discussion Starter · #1 · (Edited)
1990 cadillac deville having idling problems/running to rich

Hi i have a 1990 deville with the 4.5l i have been working on it for the past week now. It all started almost 2 weeks ago now my car started running really rough so i change the pulgs nothing change so i put new wires on and nothing changed so i moved on to the cap and rotor nothing so i changed the coil cleaned out the throdle body removed the egr to clean it out and removed the cat (it was pugled) changed the oil fulshed the trans and repalced the line that runs from the throdle body to the trans and timed the motor just to be sure it was good and still nothing so i started looking into the feul system tested the pump changed the fiter test the feul rails/injectors still nothing. Now the last few days it hasnt ilde rough at all but now it smells like its running very rich and when driving and say u slow downor come to a stop it wants to keep a high idle but then i drops after i few short seconds and then hesitates when taking off but just for a short second (almost like if it wasnt getting gas but all of that was ok) and then drives just fine it hasdrop about 4 miles to the gallon (from it running rich). the only code i have gotton and get is e 96 and i found out is Torque Converter Overstress so if anyone can help me please let me know i would hate to sell this but i need a reliable car cause i drive 36 miles one way to work and dont need any car trouble thanks
 

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1985 Sedan DeVille
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Now the last few days it hasnt ilde rough at all but now it smells like its running very rich and when driving and say u slow downor come to a stop it wants to keep a high idle but then i drops after i few short seconds and then hesitates when taking off but just for a short second (almost like if it wasnt getting gas but all of that was ok) and then drives just fine
The last time I had that problem the timing was too far advanced

Sounds like you've done everything, fixed the rough running, and now have a timing problem
 

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1990 cadillac deville
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Discussion Starter · #4 ·
Thanks for the pointer about the title ill change that asap. And the timimg is spot on right at 10 degrees btdc. the guy at the parts store tolled me about a temp sensor could be the problem. has anyone hered of that befor?
 

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1985 Sedan DeVille
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It's possible. When the engine is first started the computer runs the mixture rich until the O2 and coolant sensors indicate that the engine has reached operating temperature, and if either of them are faulty the computer will keep the car in open loop forever. There is also a temperature sensor for air in the manifold--the computer needs to know volume and density to apply the right fuel load, and it looks at pressure and temperature to calculate the density (quantity is fixed per displacement). You can use the diagnostics display to show coolant temperature and maybe air temperature (although I think it only displays the final density), which will tell you if those sensors are working correctly. You might also inspect your O2 sensor wire, or replace it for kicks if you haven't in a while.
 

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2010 DTS
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Yeah, that's one nice thing about OBDI. You can go into the PCM DATA and get all the readings that the PCM is seeing.
 

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1990 cadillac deville
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Discussion Starter · #7 ·
So i just got back from taking my car in to have it looked at well they didnt hlep me very much all they said is to change the plugs and wires lol i already did. so i came home and tested the temp, map, throdle air thing on the front of the throdle body and the tpi on the back and all of them work just fine i havnt had any codes come up. the only thing i see thats differnt is the fuel preesuer drops down to 38 psi when it running they said its to between 40 and 50 when running. I know u can look at the codes on the ccc but how do u work the other things on? thanks angain
 

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1993 Coupe Deville, 2009 XLR-V 1 of 6 Crystal Red
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Have you pulled the vacuum line from the throttle body to the pressure regulator? If it's wet with gas you need to replace it. Four MPG less is alot of gas going out the pipe and will eventually ruin the cat. Did you clean out the intake tubes when the throttle body was off?
 

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You can get into the PCM data mode, but you'll need a FSM to tell you what you are seeing. Otherwise it's just a bunch of numbers.
 

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03 DeVille
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Not sure if it's the same as my '03, but mine was idling rough and it turned out to be a vacuum leak. The boot that connects the TB to the intake had a tear in it. It was impossible to see. The way I found it I took a section of vacuum hose, put one end to my ear and moved the other over possible leaks. When I got to the leak I could hear rushing air. Hope this helps.
 

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1990 cadillac deville
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Discussion Starter · #11 ·
I did have to replace the vacum line to the fpr it was cracked i clean as much as i could get to as i only too the throttle body off anf not the hole intake. but i think i now know wat my pronblem is that air throttle sensor on the front of the throttle body the one that tells the car how much air is coming will it works prefcet when the throttle is opening but now when u let off of the throttle is dosnt move back in as fast as it comes out in fact it jerks back a little bit stops back stops back stops ect intell its all the way back in. but i took it off and tested it. as far as i can tell its good now 2 things dose it come back on its own(with spring) or under power(the motor pulls it back in) and wat controls it(how does it work?) im getting ready to go to the junk yard to look for one so if that dosent work wat do u guys think it could be? Thanks for all the input its been alot of help this is the only car to stump me so bad lol. but thanks
 

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Turbosixx -:welcome:
You are talking about the plenum. Very comon failure on the 2000+ engines and has been discussed here many times.

Sshmude -
but i think i now know wat my pronblem is that air throttle sensor on the front of the throttle body the one that tells the car how much air is coming
That would be a MAF sensor. Maybe I'm wrong, but I don't recall the 4.5 having one.

but now when u let off of the throttle is dosnt move back in as fast as it comes out in fact it jerks back a little bit stops back stops back stops ect intell its all the way back in.
as far as i can tell its good now 2 things dose it come back on its own(with spring) or under power(the motor pulls it back in) and wat controls it(how does it work?)
Sounds like you are talking about the ISC (Idle Speed Control) motor. It's controlled by the PCM. It only controls idles speed. Once the throttle hammer is off the plunger it does nothing.
 

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03 DeVille
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Ranger - Thanks for the welcome. I was a member in the past but couldn't remember my username/password so I started over. From what I've seen you have been a HUGE help to many owners and I'd like to say thanks for your time and valuable information. I"ve been a shade tree/hotrodder for close to 30 years so I'm hoping I can contribute some.
 

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1990 cadillac deville
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Discussion Starter · #16 ·
Thanks to everyone for ur input. I have found what was wrong with my car it was the idle air control valve that pices i was taking about on the front of the trottle body. It wasnt retracting right so i just got one from the junk yard off a 4.9 and now she purrs like a kitten should of done that in the frist place would of saved me a lot of time. Thanks to everyone
 

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Just for clarifications sake, that is an ISC (Idle Speed Control) motor, not an IAC valve. The IAC valve was not used on the 4.6 and not on the 4.6 until '96 or '97.
 
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