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High idle speed on 85 K-5 Jimmy computer controlled Rochester quad carb.

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by k-5 jimmy fan, Jul 28, 2004.

  1. k-5 jimmy fan

    k-5 jimmy fan Registered Member

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    On setting the TV cable the D-shaped button appeared to be sticking. I gave it & cable a shot of WD-40 and depressed the button a couple of times to made sure it was free. I depressed the D-button release and gave the cable slider a tug and it extended out easily, then pushed the cable slider back fully to the cable housing & released the D-button.

    Followed Bowtie procedure for setting TV cable, it ratcheted out only very slightly at WOT.

    After the TV cable reset the carb now idles "VERY" fast. All appears normal, all throttle components return to original settings, I have backed off to the max on idle adjusting screw, to no effect at all. I have checked all vacuum lines for major leaks, found nothing.

    To say I am confused is to put it mildly. All was fine until after TV cable adjustment. I did spray some carburetor cleaner with air filter off around the carb & plugged vac lines checking for vacuum leaks before & after making TV cable setting, could this have contributed to problem?

    Any ideas would be appreciated.
     
  2. hi pinion

    hi pinion 3/4 ton status

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    Welcome /forums/images/graemlins/thumb.gif BTW mine is doing this too, sorry i cant help, but good luck /forums/images/graemlins/thumb.gifjake /forums/images/graemlins/thumb.gif
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: High idle speed on 85 K-5 Jimmy computer controlled Rochester quad carb

    Whats the TPS reading? Somewhere around .50 volts with the throttle closed is correct, anything above that (say around .60) means the ECM "sees" the throttle open. (which it may be)
     
  4. Blue85

    Blue85 Troll Premium Member

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    Since this is a new problem, it is probably external to the carb. Check all of the linkages connected to the throttle. I have had the cruise control linkage get twisted and stick a few times. Makes it idle at about 2500rpm. Very shocking when you first turn the key /forums/images/graemlins/eek.gif
     
  5. k-5 jimmy fan

    k-5 jimmy fan Registered Member

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    [ QUOTE ]
    Since this is a new problem, it is probably external to the carb. Check all of the linkages connected to the throttle. I have had the cruise control linkage get twisted and stick a few times. Makes it idle at about 2500rpm. Very shocking when you first turn the key /forums/images/graemlins/eek.gif

    [/ QUOTE ]

    Do you ever have that one right, at my age, start up RPM runaways becomes significant emotional events. With some slack in the rear diff and a shift from reverse to ahead, (another project for another day) it do make for a slam/bang.

    I checked all linkages and seems normal, (?) for a 19 year old truck. I did disconnect the ECM to the distributor to check timing. When I restarted after the disconnect the RPM had dropped significantly, timing was out a bit, so reset. When I reconnected the ECM and restarted, the RPM was as fast as before.

    So as dyeager535 suggested, the computer sees/thinks it sees something amiss and appears to be trying to compensate. One thing I haven't done yet is disconnect the battery to clear the CPU memory and see if it forgets to speed back up.

    I have never taken a voltage reading on the TPS as dyeager535 suggested, so suppose that will be an option to take a look at.

    I am coming to hate the basically un-adjustable hermaphrodite carb with the CPU controlled 1980's environazi's wet dream garbage. I think it is getting time to go for manual and mechanical swap out. Need to investigate as to cost, expertise and effort for parts & etc.
     
  6. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    I am coming to hate the basically un-adjustable hermaphrodite carb with the CPU controlled 1980's environazi's wet dream garbage. I think it is getting time to go for manual and mechanical swap out. Need to investigate as to cost, expertise and effort for parts & etc.

    [/ QUOTE ]
    It's a stupid setup IMHO. My '85 had it and I removed it and as far as how it runs I never looked back but the problem is smog. Mine won't pass now(visual, not emmissions). /forums/images/graemlins/tongue.gif
    The worst part about the CCC systems is with the combo of a carb and computer system equals the drawbacks of both a computer controlled FI system without the benifet of actual FI but still get the less power, nat as smooth running, bad mileage, yada yada...that you get with a carb.
     
  7. trailblazer86

    trailblazer86 1/2 ton status

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    Are you sure this is a computer controlled carb?
    I have an '86 and it only has two wires running to the front of the carb and one wire running to the choke.
    If this is what your set up is like then the wires at the front only control the fuel shot from the accelerator pump.
    During warm up the carb gets a larger measurement of fuel.

    As for the T.V. cable, make sure that all of your idle screws are not holding the throttle open and then start adjusting the T.V. one click at a time until it is properly set. (You would be better off using a pressure gauge to set your T.V. cable)

    www.transmissioncenter.net/700r4.htm

    This is a great page about how to take care of a 700r and how to set the T.V. cable. The article is well worth the read.
     
  8. k-5 jimmy fan

    k-5 jimmy fan Registered Member

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    " www.transmissioncenter.net/700r4.htm

    This is a great page about how to take care of a 700r and how to set the T.V. cable. The article is well worth the read..."

    From what I understand the carb is of the feedback type & idle is controlled by the ECM. When I time the engine I disconnect the ECM connection to distributor & plug any lines that pull a vacuum. Set timing to 6 degrees BTDC, it will then idle great with the ECM disconnected. (idle would not change to normal at this time would it, if any mis-adjusted idle stops or other adjustable mechanical components were at fault?) I then shut off engine, reconnect the ECM to distributor and restart. Almost immediately the RPM will climb to 1500 & up at idle.

    On non-ECM carb engines I never worried about timing marks & such, just set the timing with a good vacuum gage at normal idle & it always worked out great.

    /forums/images/graemlins/waytogo.gifThat is a great page, sure firms up other's input that all tranny components are parts of an integral system, change one thing, and the effect for good or ill is transmitted & felt throughout.
     

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