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Its a 92 STS 4.9L
it idles around 900-1000 cold
when warm it idles around 500-525ish but a few times its stalled

the Idle screw at 500 idle isnt even touching the Throttle body has been serviced when the last owner had it

The IDLE srew is about an 1/8th of an inch away from the throttle bracket No way touching and i can buy the tool from the dealer has anyone done this and know what the screw is
is it like 1 8mm hex a flat screw driver a phillips head screw driver is in the worst are to try to get to any help would be great

Thanks BOB
 

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'90 DeVille '97 DeVille
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The Chilton manual for my '90 DeVille 4.5 indicates a Torx T-20 for the min idle speed screw and a Torx T-25 for the TPS (Throttle Position Sensor) fasteners. The ISC plunger screw is not an idle speed adjustment; rather it is a potentiometer that changes voltage sent to the TPS. Shop manual gives procedures for adjusting min idle and TPS.
When my 4.5 was stalling, new O2 sensor cured it. Cleaning throttle bore and throttle plates with toothbrush and solvent and installing new cap and rotor helped too. I also cleaned the EGR tubes while I was at it. Then perform idle relearn (unhook battery 30 sec, reconnect, warm engine in Park 15 min, hold foot on brake while in Drive for 3 min)
Good luck!
 

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The minimum idle screw should not be turned.
The ISC controls the idle speed. Turning those screws has little or no effect except to mess up a factory setting that wasn't meant to be changed.
The computer controls the idle speed.
If it's too high or too low you need to find out why the computer is not controlling the idle right. Don't start adjusting things that weren't meant to be adjusted.

Setting the minimum idle screw also requires a few special tools to make sure the setting is correct.
 
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