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idle speed


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hi! when first starting 94 etc car idle is about 1200. if the weather is cool idle drops to about 700 and also lowers on deceleration. if weather is hot (85+) most of the time idle stays about 1200 and is very slow to lower, with foot off of gas car runs almost 40 mph or about 1700 rpm. sometimes it will act normal. a few times after driving and stopping then restarting car idle will drop to 0 and die.

any help greatly appreciated. thanks rich

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normally idle should higher when it cool. then it goes down when the engine warms up to working temperature (around 600 RPM). It is always lower while in a gear.

Pool the codes you'll get some idle speed control related codes. perhaps you need to perform IS learning procedure, but first push Warmer and OF buttions simultaneouusly for a few seconds until the DIC starts giving information. Write down what you see and post here, we'll try to help.

The saddest thing in life is wasted talent

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happened again this morn.

there are no pcm codes or any other. drove for about 10 min, shopped maybe

1/2 hr then idle was 1250, water temp 220, outside temp 84. driving 45mph

and letting up on gas, car does not slow down. tried for codes again tonite

still none

thanks rich

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It sounds like the closed throttle switch on the idle speed control motor is acting up. Do a search in the archives on ISC or idle speed control and read up.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I agree with KHE, for the moment I would rule out the tps (throttle position sensor) because you would get a code if there was high voltage problem. First check and clean the isc, check the pintle length if all the way extended replace the isc. Another problem is that when a engine is cold it is in open loop once it warms up it goes to a closed loop mode. It seems that your engine is returning to open loop mode the main things to check for this are the water temp sensor and the oxy sensor both of these can be checked with a digital volt ohmmeter with a impedance of 10,000 ohms per volt. Mike

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thanks

problem solved. i disconnected the battery then removed the idle speed control, completely diassembled, degreased, and cleaned the whole unit. i then lubricated and re assembled, then reinstalled the unit and battery. everything worked fine but then i had every rss code showing. i then disconnnected the battery and waited aprox 1/2 hr and carefully reconnected the battery. after 3 days of stop and go driving i have no codes and all rpm's are normal.

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