4.9 Will Not Idle Below 2500rpm! - Page 2
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HT4100 4.1, 4.5, 4.9 Discussion, 4.9 Will Not Idle Below 2500rpm! in Cadillac Engine Technical Discussion; Yeah, MAP of 103 kpa is typical around sea level (where I am). I usually observe 100-103 in my Caddy. ...
  1. #16
    peteski is offline Cadillac Owners Enthusiast
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Yeah, MAP of 103 kpa is typical around sea level (where I am). I usually observe 100-103 in my Caddy.

    But is "ED08 Spark Advance -- 34 Degrees" normal at idle (in those engines)?
    ANd how about "ED70 Cruise Control Feedback -- 22%"?

    Since I don't have a 4.9l car - those are just my observations.

    Peteski

  2. #17
    skor is offline Cadillac Owners Member
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    Re: 4.9 Will Not Idle Below 2500rpm!

    OK, here's the update.

    I replaced the fuel pressure regulator, and that had no effect. The car still idles at 1250-1300 rpm.

    For those of you who keep chanting ISC motor, forget it, that's not the problem. If you read my previous posts, you'll see that I replaced and adjusted the ISC motor. Secondly, the ISC motor does not move while the idle surges up and down. If the ISC is not moving, WHAT IS CAUSING THE IDLE SURGE?

    For those of you who live by minimum idle air screw molestation, that's a ghetto solution. The minimum idle speed screw does not go out of adjustment all by itself all of a sudden.

    WHAT ELSE CAN CAUSE THE IDLE SURGE? That is the $64K question.

  3. #18
    Raze's Avatar
    Raze is offline Cadillac Owners Enthusiast
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    Re: 4.9 Will Not Idle Below 2500rpm!

    I'm watching this thread...

    bump to keep it on top

  4. #19
    kdcing is offline Cadillac Owners Fanatic
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    Re: 4.9 Will Not Idle Below 2500rpm!

    When the engine is @ 1250-1300 rpm, is the throttle cam pressing up against the ISC plunger?

  5. #20
    skor is offline Cadillac Owners Member
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Well, I found out what was wrong, car is working normally now. Since none of you will believe me if I tell you what was wrong, I won't tell you.

  6. #21
    cadillac_tech is offline Cadillac Owners Fanatic
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Oh come on! Don't leave us hangin'. What was it?

  7. #22
    kdcing is offline Cadillac Owners Fanatic
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Quote Originally Posted by skor View Post
    Well, I found out what was wrong, car is working normally now. Since none of you will believe me if I tell you what was wrong, I won't tell you.
    So the floor mat was bunched up on the gas pedal? It's happened to all of us!

    Go ahead and 'fess up....we all can learn from it.

  8. #23
    peteski is offline Cadillac Owners Enthusiast
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    Re: 4.9 Will Not Idle Below 2500rpm!

    If that was the case he would never see the "idle switch closed" LED light up.
    He better tell us what happened - we all tried to help and gave him our time. Maybe it was a vacuum leak - maybe he left his PCV valve hose disconnected.

    Peteski

  9. #24
    HUF's Avatar
    HUF
    HUF is offline Cadillac Owners Connoisseur
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    Re: 4.9 Will Not Idle Below 2500rpm!

    He should be banned for knowing what happened and not telling us! Just kidding. lol

  10. #25
    skor is offline Cadillac Owners Member
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Never assume that the new replacement parts that you buy are actually good. The after-market ISC motor that I bought was defective out of the box.

  11. #26
    awadecki is offline Cadillac Owners Enthusiast
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Haha, I've learned this lesson too many times owning 4 older GM cars. I will never again buy non-AC Delco ignition modules, pick up coils, EGR valves, alternators, starters, or anything else that is readily available.

    I've been burned too many times by crappy "lifetime warranty" replacement parts that fail less than 3,000 miles later.

    The worst offender that I've found are Bosch alternators and starters. I went through 3 alternators in 3,000 miles on my 91 Deville before I sold the car and 2 starters before I finally put a Delco-brand on. The worst part was that two alternators failed mechanically (bearings burned out, snapped my serp. belt), and one failed electrically.

  12. #27
    kdcing is offline Cadillac Owners Fanatic
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Good to hear that the car is running correctly.

    Do you recall if the engine returned to normal idle within a minute or 2 of replacing the ISC or was it necessary to get the idle down to 425-450rpm by manually getting the ISC plunger to retract? I fought w/ my ISC for 3 months before I finally found an article online which specified the 425-450rpm requirement.

  13. #28
    peteski is offline Cadillac Owners Enthusiast
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Quote Originally Posted by skor View Post
    Never assume that the new replacement parts that you buy are actually good. The after-market ISC motor that I bought was defective out of the box.
    Interesting. So the new ISC was defecive even though it's idle switch was working properly and in it fully extended and retracted while in the test mode? That is really odd.

    But the important thing is that the car is fixed!

    Peteski

  14. #29
    cadillac_tech is offline Cadillac Owners Fanatic
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Quote Originally Posted by peteski View Post
    Interesting. So the new ISC was defecive even though it's idle switch was working properly and in it fully extended and retracted while in the test mode? That is really odd.



    Peteski
    Oh yeah, we're all gettin jacked here. Something too simple to admit was overlooked. Where's the humility?

  15. #30
    skor is offline Cadillac Owners Member
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Quote Originally Posted by cadillac_tech View Post
    Oh yeah, we're all gettin jacked here. Something too simple to admit was overlooked. Where's the humility?
    The new ISC did fully retract and extend. The throttle switch also worked. After retracting the ISC through the ECM override, I noticed something peculiar. The throttle cam was not on the min air screw even though the ISC plunger screw was turned in as far in as it would go.

    At this point, I removed the ISC plunger screw from the new ISC plunger and compared it to the screw from the old ISC motor. The plunger screw on the new motor was significantly longer than the screw on the old ISC motor. I installed the old ISC plunger screw in the new motor, did the adjustment and idle relearn, and all is now well.

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