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1990 DeVille, 1993 DeVille
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Discussion Starter · #1 ·
With my '90 Deville, I am experiencing a rich fuel mixture, as well as the idle control solenoid keeps the throttle open until after i come to a complete stop, then it releases.
For now my three questions for anyone who knows:
--What data (or sensor) tells the idle control to open or close? I assume it gathers from the TPS, but is there a speed sensor involved also?
--For rich fuel trim, on cold mornings it cranks and runs perfect. In the warmer afternoons its rough and stumbles some, so my halfway educated guess is the ambient air temp sensor thinks its 29 degrees out all the time and is dumping fuel, just looking for confirmation on this thought process.
--Air diverter valve....has anyone had luck cleaning these, and what process did you use. Im thinking cut it apart at the factory plastic welds, then epoxy back together once clean.

Thanks for any info the group can give, this is a daily beater, but sure would be nice for it to run right with no huge amber engine light for the car next to me to see.
 

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2010 DTS
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What data (or sensor) tells the idle control to open or close? I assume it gathers from the TPS, but is there a speed sensor involved also?
No


Air diverter valve....has anyone had luck cleaning these, and what process did you use. Im thinking cut it apart at the factory plastic welds, then epoxy back together once clean.
If it's bad, I'd just replace it.


For rich fuel trim, on cold mornings it cranks and runs perfect. In the warmer afternoons its rough and stumbles some, so my halfway educated guess is the ambient air temp sensor thinks its 29 degrees out all the time and is dumping fuel, just looking for confirmation on this thought process.
I think a bad ambient air temp sensor should set a DTC.
Check the two fuel injectors in the TB. They should PULSE the fuel. If you se a steady stream, you may have a stuck open injector.
Also check the two EGR tubes down in the TB to be sure they are not carboned up as pictured below. If so, for them out with a coat hangar or drill bit.
P.S>
This picture is of the 4.9, not positive, but I think the 4.5 might be the same.

Circle Metal Steel Aluminium
 

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89 Deville, 06 DTS
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188 Posts
What data (or sensor) tells the idle control to open or close? I assume it gathers from the TPS, but is there a speed sensor involved also?
There's a few parameters, per my '89 Deville. I'd have to check the FSM to be sure, but there's a few parameters. The engine is set to maintain a specific RPM, and will open or close the IAC motor to maintain that. The set RPM will change based on certain things such as AC compressor selected ON/OFF, or even how much you're trying to turn the wheels.

For rich fuel trim, on cold mornings it cranks and runs perfect. In the warmer afternoons its rough and stumbles some, so my halfway educated guess is the ambient air temp sensor thinks its 29 degrees out all the time and is dumping fuel, just looking for confirmation on this thought process.
Per the FSM for my '89:
The fuel control system is made up of the following parts:
- Information sensors:
  • Coolant temperature sensor
  • Manifold Absolute Pressure (MAP) Sensor
  • Manifold Air Temperature (MAT) Sensor
  • Oxygen (O2) Sensor
  • Throttle Position Sensor (TPS)
  • Vehicle Speed Sensor (VSS)
  • Engine Speed Sensor (DIST)
  • Park/Neutral Switch
  • Power Steering Switch
  • Battery Voltage Input
The ambient temp sensor isn't part of this list. Your MAT however, is. It's screwed into the manifold up near the alternator. A quick check of the onboard diagnostics should give you the reading off this sensor

Air diverter valve....has anyone had luck cleaning these, and what process did you use. Im thinking cut it apart at the factory plastic welds, then epoxy back together once clean.
I wouldn't bother. The only thing going through there should be clean air, unless, of course, your check valve has gone bad. In those cases, you usually end up ruining the air diverter valve. Most often, you'll find the rubber diaphragms inside starting to go bad, as they crack with heat and age. Finding replacements are difficult. Hit up a junkyard. In any case, these rarely cause runability issues, just failed emissions tests.

What code is the check engine light setting for?
 

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1990 DeVille, 1993 DeVille
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39 Posts
Discussion Starter · #4 ·
Ranger.
The air diverter for 1990 is unobtainium, and I could buy one, but it would cost more than I paid for the car, so I cant, with a good conscience, do that. I found a thread in a dead forum where the poster had disassembled the diverter, cleaned out the foreign material (smog pump impeller shards) and reassembled. However the thread is so old, the pictures are gone. I have dumped as much of the shards out of mine as i can, but i feel like the valves still have material stuck.

cksnyder,
manifold air temp is what i was trying to find,everyone calls it something different for the same thing. i feel like the computer thinks its cold at all times.
The code is 049 for the diverter valve.
 

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2010 DTS
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I have dumped as much of the shards out of mine as i can, but i feel like the valves still have material stuck.
Before you attempt to disassemble and reassemble it, maybe spray some Brakleen in it and shake it like you would when cleaning an old rattle can PCV valve. That might do it.
 

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89 Deville, 06 DTS
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188 Posts
Are you sure your car is going closed loop? Not doing so would cause rich running. Bad thermostat or coolant temp sensor causes this. Can be verified through onboard diagnostics
 

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1990 DeVille, 1993 DeVille
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Discussion Starter · #7 ·
I have changed out the air and coolant temp sensors, I cheated and didn't test them first, but it has made a huge difference in the sound and engine smoothness. I still have a rough cold start, rich idle and slight hiccup on take off. I haven't checked the tps adjustment yet. Do you know what the volts or ohms should be at idle and wot
 

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1990 DeVille, 1993 DeVille
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39 Posts
Discussion Starter · #8 ·
Does anyone know what controls the fuel on cold starts? Warm starts are much improved, cold starts are terrible now. I am also getting an intermittent O2 sensor code and would like to inspect my grounds, if anyone has the chart for ground locations, or known bad ground locations.
 
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