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Hesitation, rough idle problem on 93 K1500 350TB

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by MitchellB, Jan 14, 2011.

  1. MitchellB

    MitchellB New Member

    I'm trying to figure out what has suddenly caused my 93 Suburban to have a rough idle and when I mash on the gas it wants to go dead? If is accelerate very slowly often it will catch and run OK. Changed fuel injectors, spark plugs (they had fouled), cap, rotor, fuel relay was bad and changed that, changed fuel pump & fuel filter and a broken vacuum line elbow at PCV valve. All these changes improved, but did not cure my problem. Any ideas where to go next? I have read bad EGR, MAF, MAP, Oxygen, TPS sensors and even a coil can cause this problem.
  2. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    I would do a sweep test on the TPS just to be sure it is testing good. Also did you clean the throttle body out well when you did the new injectors? and is the CEL on? if so then you will want to pull the codes which will give you the most info.
    But you will want to take a much closer look at the pickup coil, under the rotor. That is what advances your timing and it may be cooked so it isnt advancing the timing as quickly as it needs to for hard acceleration.
  3. MitchellB

    MitchellB New Member

    Thanks for the response. I clean the throttle body out somewhat with spray carb cleaner, although I did not remove from the engine it to replace the injectors. The Check Engine Light is not on either. How do I retrive the codes on this vehicle? Do I have to have a device or code reader to hook up to it?
  4. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    NOpe there is a thread that tells you how to do it, and a paperclip is all you need, however if the cel isnt lit then you dont have any codes to pull.
    As to the Throttle body i would pull it off and clean it up really good. Use throttle body cleaner as well not carb cleaner. Carb cleaner actually removes some of the plating on the TB. be sure to clean the IAC passage really well and be sure it can seat up tight.
  5. MitchellB

    MitchellB New Member

    Worked on the old truck some more today. I checked the TPS and got an intermitten reading in a couple places, so I went ahead and replaced it. Didn't help though.

    I'm beginning to think it has something to do with the air/fuel mix. I pulled the vacuum line off the PCV valve and the old truck picked up and run smooth. As soon as I plug or re-connect the line it boggs down again. I was thinking maybe something to do with the EGR or the device in the vacuum line between the EGR and vacuum port on the throttle body (MAP or MAF?) Anyway I took the device off. The two electic connections reads zero resistance or a simple closed circuit. The vacuum line (side that goes to port on TB) appears restricted, but I'm not sure if it is opened by the current passing through it or not. The other side of the device (vacuum line goes to EGR) is open, but air is comes back out a port on the same side of the device and not through to the oppsite vacuum line.

    Thanks for tips, but I'm not sure I know what the IAC passage is?
  6. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    Idle air control valve. and there is a chance that your PCV valve is plugged, which can cause the motor to run poor. If you shake the PCV valve does it rattle? if not then it is completely plugged.. but it wouldnt be a bad ideal to just go and clean things up.
  7. Looey

    Looey Rockstar

    You should check the ignition timing. You have to disconnect the timing plug which is located on the passenger side firewall along with the relays. It should be set at 0* with the plug disconnected.
  8. MitchellB

    MitchellB New Member

    Thanks again for the response. I had to look up IAC valve to find it. I may replace it. I did check the PCV valve and it seemed OK, but replaced it just to be sure. I can't imagine the timing being off without having moved the distributor shaft or the timing chain is loose. It was just sitting in the driveway. One day it run good, the next day I had problems.
  9. MitchellB

    MitchellB New Member

    Well, I finally give up and paid someone who knows more about vehicles than me to fix it. I just got it back last night. As it turned out, one of the new NAPA fuel injectors I installed was leaking and had to be replaced, and a temperature sensor had to be replaced. I doubt I would have caught the temperature sensor problem, and although I replaced the injectors, I never thought one of the new ones would be faulty. The reason I went to NAPA in the first place is the quality is usually better than most of the other parts stores. It was certainly expensive enough to be better. Anyway, the old “bourbon” runs better than ever now. Thanks again for all the input.

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