Mechanics

HIGH IDLE

1998 Cadillac Deville

Engine Performance problem
1998 Cadillac Deville V8 Front Wheel Drive Automatic 113 miles

how do I Perform  the  IAC  Valve  learn  procedure  cadillac I changed the iac and maf and some hoses and still I have a high idle how do I reset the system to get the right air flow
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Bigbill3975
September 22, 2009.




You have an idle speed control motor( ISC) on your vehicle. It is also called servo.
You're right, you will need some adjustment of the TP sensor to get the ISC right.

To Perform the TP sensor adjustment.

Disable the generator by grounding the green harness connector plug adjacent to the generator.
Start the engine, enter diagnostics, and select PCM override PS103 'ISC Actuator'
Press the 'COOLER' button on the CCP to retract the ISC Actuator. This action will disengage the A/C compressor and command the EGR 'OFF'. The Climate control center display will change from '50 to 00'. The ISC Actuator will slowly retract (about 20 seconds) to a fully retracted position. Verify that the throttle lever is resting on the minimum idle speed screw. With the ISC Actuator plunger fully retracted, disconnect the ISC harness.
Select the PCM data PD01, 'TP Sensor', while still in PCM override PS03. Note the throttle position (in degrees) displayed on PCM parameter PD01.
(-0.5 TO + 0.5 )

Tiny
Mathiaso
Sep 22, 2009.
98 does not have ISC, that went out in about 1996 on the Devilles. If the IAC valve is disconnected or disabled with the engine running, the PCM may loose track of the IAC valve position causing erratic or incorrect idle speed. If this occurs, reset the IAC valve by doing the following: The coolant temperature must be above 0 C (32 F)
The vehicle must be in Park (P) not Neutral (N)
Turn the ignition switch to Lock for 20 seconds

Do you have a vacuum leak causing the high idle?

Factoryjack
Sep 22, 2009.
How are you doing gstacey
Cadillac Deville 98
4.5L and 4.9L Engines does according to my source have ISC. You are talking about 3.0 L. For the same year.

The ISC motor is calibrated at the factory. It is a nonservicable unit. Do not attempt to disassemble it. Do not immerse the ISC motor in any type of cleaning solvent and always remove it prior to cleaning or servicing the throttle body. Immersing in cleaner will damage the ISC unit.

Tiny
Mathiaso
Sep 23, 2009.
In 98, the only options for engine size was 4.6l Northstar in either VIN 9 or Y. Don't know your info source, but it is incorrect.

Factoryjack
Sep 23, 2009.
Ok I'm back
I found the mistake, look at the wrong page for1994 CADILLAC DEVILLE 4.9L v8.
Look on 94 instead of 98.
You are right. Thank you for catching the mistake.

Now let help Bigbill3975 to diagnose the problem.

Poor connection IAC motor. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Inspect the wire harness for damage, including; proper routing, broken insulation, rub through, or broken wires. A restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element, or foreign objects blocking the air intake system. Check the throttle body for objects blocking the IAC passage or throttle bore, excessive deposits in the IAC passage and on the IAC pintle, and excessive deposits in the throttle bore and on the throttle plate. Check for a sticking throttle plate. Also inspect the IAC passage for deposits or objects which will not allow the IAC pintle to fully extend. Check for a condition that causes a vacuum leak, such as disconnected or damaged hoses, leaks at the EGR valve or EGR pipe to intake manifold, leaks at the throttle body, faulty or incorrectly installed PCV valve, leaks at the intake manifold, a brake booster hose that leaks or is disconnected, or a faulty component that uses engine vacuum to operate.
Inspect the hoses you changed, make sure the clamps are tight. Make sure the small rubber ring around the IAC is there.
Let me know if you have questions.
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Tiny
Mathiaso
Sep 23, 2009.

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