What does the code po85 mean for a 1994 cadillac deville

It means that the throttle body is dirty and the deposits in the throttle bores are restricting air flow at idle to the point that the idle speed control has no more authority to maintain the correct idle speed.

Take the air cleaner off, hold the throttle wide open and look down the throttle bores. Spray the throttle bores with carb cleaner and scrub the bores and backside of the throttle blades with an old toothbrush. Cleaning the deposits off the bores and throttle blade backsides it will restore the idle air flow to the correct level. When the throttle body is clean, disconnect the battery negative cable for 60 seconds to reset the idle learn offsets to the "clean throttle body" default values.

While you are in the throttle body and looking down the bores....see the two tubes sticking up at you from the intake manifold floor just below the throttle blades...??? Those are the EGR tubes and they are NOT supposed to be full of carbon and crud. Rod them out thoroughly with a piece of stiff wire to remove the deposits. Go all the way down thru the tubes to the cast passage below and make sure that they are clean and unrestricted so that the proper amount of EGR can flow.

Turning the key to the run position extends the ISC anticipating a restart, so if the setting is incorrect it would not erase a hard code. Just turning the key to run would light up both the service soon and service now lights as a bulb check, in other words, letting you know the bulbs work. Do you have the factory service manual?

The ISC adjustment is simple on this car. With the engine running and at operating temperature, You raise the throttle arm slightly with your right hand and push the shaft of the ISC in to fully retract it with your left hand. With constant pressure on the ISC shaft it will slowly retract. The very second it bottoms, you quickly remove the wiring connector to the ISC. Now you should have a very low idle and a gap between the throttle arm and the tip of the ISC. Approx. 0.060 of an inch. Once you know the gap is correct, shut off the engine, wait 10 seconds and reconnect the ISC wiring. Restart the engine and the ISC is set to spec. The TPS setting must be verified at this time. At minimum idle, ISC not touching the throttle arm, and unplugged, the TPS should be reading approx .0 or .1. Once the ISC is reconnected, you should see a TPS reading of approx. .5 at idle. with the A/C off.

A hard code can be erased but will continue to reset as long as the reason for it has not been corrected. Idle learn procedures were designed into later year engines with multi port fuel injection to adjust idle regardless of the amount of coke build up within the throttle body. Your fuel injection system does not build up coke or deposits because the 2 injectors spray down thru the throttle body, effectively cleaning the throttle body while running. Alot of owners adjust the ISC as if it were a throttle stop screw on a carb. guessing as they go. The ISC and TPS "MUST" be in sync to get the best off throttle response and smoothest idle. Adjusting the ISC without verifying gap or TPS voltage usually results in a surging or too high warm idle. You say the car failed at idle. For what reason? CO or HC? or idle too high?

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