4.9 has irratic idle can you help
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HT4100 4.1, 4.5, 4.9 Discussion, 4.9 has irratic idle can you help in Cadillac Engine Technical Discussion; I have a 1992 fleetwood the engine was replace with a used engine. When i start it cold it idles ...
  1. #1
    Wolfpath2004's Avatar
    Wolfpath2004 is offline Cadillac Owners Fanatic
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    Question 4.9 has irratic idle can you help

    I have a 1992 fleetwood the engine was replace with a used engine. When i start it cold it idles just fine. once the engine warms up the engine idle goes up and down. the idle speed controler goes in and out sometimes to keep the engine running..what is the problem?

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    ehall's Avatar
    ehall is offline Cadillac Owners Connoisseur
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    Re: 4.9 has irratic idle can you help

    You need to get the ISC calibrated. Smaller shops don't always know to do it.

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    Wolfpath2004's Avatar
    Wolfpath2004 is offline Cadillac Owners Fanatic
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    Re: 4.9 has erratic idle can you help

    the isc only goes in and out when the idle drops almost to the point of stalling

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    awadecki is offline Cadillac Owners Enthusiast
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    Re: 4.9 has irratic idle can you help

    hard to pinpoint your problem without more info. could be the oxygen sensor (only read by the computer when warm), could be a failing closed throttle switch in the isc, could be a bad ground. check the engine block grounds first. make sure your 02 sensor toggles between rich and lean.

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    Wolfpath2004's Avatar
    Wolfpath2004 is offline Cadillac Owners Fanatic
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    Re: 4.9 has irratic idle can you help

    Well my battery has a bad connection at the posts...im going to clean them up and secure them ...I'll get back with you on the results

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    NickySantoro is offline Cadillac Owners Fanatic
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    Re: 4.9 has irratic idle can you help

    Quote Originally Posted by Wolfpath2004 View Post

    ...... once the engine warms up the engine idle goes up and down. the idle speed controler goes in and out sometimes to keep the engine running..what is the problem?
    I'd look for a vacuum leak very carefully.

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