1995 Cadillac Deville - 4.9L High Idle

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Tim Martin
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1995 Cadillac Deville - 4.9L High Idle

Post by Tim Martin »

A customer brought in a 95 Cadillac DeVille with a 4.9L power plant and 109,000 miles on the clock.

The issue is when he is driving and he gets to a stop sign or traffic light and needs to stop, the engine is at 1200-1500 rpm and stays there. Sometimes it will not kick down at all unless the engine is turned off and restarted. Now, this is another one of those vehicles that has been elsewhere and by going with what the customer says, the idle speed motor, (no IAC on this one) has been replaced twice already. No difference. It starts well, runs very good, not trouble codes in the PCM except when the engine has the high idle, a code PO52 pops up. However once the engine is shut off, the code PO52 disappears. Fuel pressure is within specs, tps is at 1% (koeo or idle), for whatever reason it only gives percent and not actual voltage. I am thinking that the PO52 code may be a clue as to why the intermitant high idle, or am I off? But, not having as much experience with the Cadillac lkine as with other brands of GM vehicles I am somewhat puzzled as to what to look for. Also, MAP reading is at 1.09volt at idle in neutral and no load. Idle speed in park is 650rpm. The guy brought it to us because he was referred to us by another shop sometime back.

What do I look for on this one?
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steven kiser
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Re: 95 Deville High Idle

Post by steven kiser »

There may be a slight vac leak under the throttle body, incorrect pcv valve and in some cases intake gaskets leaking. If the idle motor hasn't been set up correctly it will roam quite a bit. There is a specific way of setting it up and if it's not followed things will go bad. If the timing has been set incorrectly it will cause issues like this.
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