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1988 dodge w150 idle problem

Discussion in 'Pre-1994 trucks, commercial vehicles' started by upser145, Jan 16, 2017.

  1. upser145

    upser145 Member

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    Also there is a something maybe some kind of sensor on the bottom of my passenger side exhaust manifold looks more like a vaccum advance then a o2 sensor. it has a vaccum line run to something on the firewall not sure what exactly it is that it is run to may upload a picture tommorow when its light out. but any ideas what this would be I'm assuming a O2 sensor since its in the exhaust manifold
     
  2. ImperialCrown

    Level III Supporter

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    It sounds like a vacuum operated manifold heat control valve. Instead of the bi-metal spring, they used a timed vacuum to an actuator to heat up the floor of the intake manifold during warm-up.
     
    Bob Lincoln and pt006 like this.
  3. pt006

    pt006 Active Member

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    I would verify 12V at the plunger solenoid wire whenever the ignition key is on. Swapped wires? The solenoid wire should be -------------- dark green/light green tracer. The choke heater wire [a larger wire] should be dark blue/red tracer.
     
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  4. upser145

    upser145 Member

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    Imperialcrown you hit the nail on the head it is the heat control valve. would the electric choke being unplugged effect the solenoid. someone that was helping me work on it broke the plug in the goes to the choke heater and i hadn't picked up another yet. I will check the wires
     
  5. upser145

    upser145 Member

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    after messing with it some more it seems the soilenoid works fine until I drive it maybe half and mile and the truck warms up then it acts like it loses power. I can turn the switch on in my yard and not crank the truck and the solenoid will stay on all day. I'm stumped. I checked and it seems to have the correct wires run to it.
     
  6. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    Start it and monitor the 12V at the solenoid. See if the 12V goes away when the solenoid appears to retract or the idle drops.
    It sounds to me like your truck has or had the electric choke heating element, and perhaps someone has miswired the truck so that the solenoid is now powered by the wire that powers the choke heating element. That would explain why the wire de-energizes after 45 seconds. The heating element was on a timer.

    Is there another wire with a single Faston terminal near the carb, that's not being used? Or is connected to the choke heating element? If so, swap the wires.
     
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  7. upser145

    upser145 Member

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    Well i think i got my idle problem right thanks for the help guys. really helped me out alot
     
  8. upser145

    upser145 Member

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    one thing that baffles me is it is said in my haynes book the throttle plates will bind if you turn the curb idle screw all the way down but ive always had mine far down as the mechanical linkage would let throttle go down and pretty much disable idle solenoid. is that normal lol
     
  9. ImperialCrown

    Level III Supporter

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    I don't have a high opinion of either Haynes or Chiltons manuals. They are too generalized and sometimes inaccurate or just plain wrong for the model you are working on. The factory shop manual is much more detailed and accurate.
    This is a Rochester Quadrajet? The chance of throttle plate/choke linkage binding is remotely possible, but may not happen. I think that the manufacturer (GM) tried to make the carburetors safely move from fully closed to fully open with no chance of anything binding or sticking.
    Of course on a 29 year-old truck with an unknown past, anything is possible.
     
  10. AHBGuru

    AHBGuru Active Member

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    This is what Chrysler called a "step-up" solenoid. As indicated elsewhere, its purpose is to bump up curb idle to about 800 RPM when the A/C or rear defrost are on.

    It is on a timer, controlled by the choke heater, located on the manifold, behind the carb, inline with #6 hole.
     
  11. AHBGuru

    AHBGuru Active Member

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    Excellent point -

    I had an '85 Fury squad that came from the factory with the wiring swapped.
     
  12. AHBGuru

    AHBGuru Active Member

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    You're getting your two idle screws mixed up.

    The curb idle screw should barely touch the cam that opens the plates at warm curb idle. I always adjusted any of my older Mopars, whether QJet or TQ, to run this way. Most of that kind of tuning was getting the timing and mixture dead-nuts, which requires a good bit of farting around - but with today's tools, should be easier.

    The A/C (step-up) solenoid is *only* used for bumping up curb idle under heavy-load idle conditions. It is adjusted last, after timing, mixture, and curb idle are set. Your curb idle, which should be on the emissions sticker, is probably around 650-675 RPM. A typical solenoid setting should be 800-850.

    Older ThermoQuads with Lean Burn came without a regular curb idle screw, so you did use the solenoid to adjust idle on those vehicles (just one idle setting). Most trucks, and all Quadrajet cars (squads) and trucks have an idle plus a solenoid to adjust. Just make sure when adjusting the curb idle that the solenoid is grounded (you can use a piece of paper, plastic, rubber, etc) or simply back out the screw enough so it doesn't touch its cam.

    For all of the flack that the last (85-89) ESC/EFC systems and TBI catch, fine tuning something like this is still a very methodical, fussy process. But you can definitely get this thing running great.
     

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