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98 1500 chugging running eratic

Discussion in 'Truck & Equipment Repair' started by amcolandscaping, Oct 17, 2008.

  1. amcolandscaping

    amcolandscaping Member
    Messages: 31

    i have a 98 1500 and if i keep her at a steady speed lets say i keep it at 40 i feel it chugging, and if i watch the tach it will be at 1000 rpms and go up 3 clicks then back to 1000 then up 2 or 3 lines then back to 1000. If i accelerate i dont feel it, it seems to run fine as i am increasing speeds. I replaced the pcv valve and now i am thinking of replacing the egr valve. any other ideas. I do have high mileage on this truck 172k but other than this and a small leak in radiator she runs good!

    HELP!!! trying to get her ready to plow

  2. SnoFarmer

    SnoFarmer PlowSite Fanatic
    from N,E. MN
    Messages: 7,921

    look for a vac leak first those plastic lines going to the cruise controll etc are known for cracking.. Then i would suspect the TPS.
  3. amcolandscaping

    amcolandscaping Member
    Messages: 31

    whats the tps?
  4. tom_mccauley

    tom_mccauley Senior Member
    Messages: 465

    and after the TPS look at the IAC

    NICHOLS LANDSCA PlowSite Veteran
    Messages: 4,286

    I had a 96 that was doing the same type of thing, was a bad spark plug. Under a load or at idle it was fine but when you lugged the motor it would miss. Good luck.
    BTW, tps is the throttle position sensor
    iac, is the idle air control
    Last edited: Oct 17, 2008
  6. sechracer

    sechracer Senior Member
    Messages: 478

    Also, might want to post what type of truck and what motor you have. Each has their own little quirks....
  7. amcolandscaping

    amcolandscaping Member
    Messages: 31

    sorry its a 98 1500 z71 with the 305
  8. sechracer

    sechracer Senior Member
    Messages: 478

    When is the last time you did a tuneup? The distributor caps on these trucks suck, poor design imo. I had one bad from the box and it wasnt noticable, it acted exactly like yours, no codes, just kept running like crap.... only reason I knew what it was is because a friend that works at a chevy dealership told me he had seen it a few times and guessed the first time.

    The "lines" inside the cap are so close that if there is a thin spot in the plastic between them, it will eventually wear out and start arcing between them at random, so no code comes up.... If you have not done a tune-up lately, I would go get a cap and rotor from the dealer (better off with oem for these) and try it...... I usually dont like to reccommend throwing parts at something, but if it hasnt been done lately, it wouldnt hurt it.

    BTW, 172k aint bad, Im at 198k on mine and it still runs strong.
  9. terrapro

    terrapro PlowSite Veteran
    from MI
    Messages: 3,868

    throttle positioning sensor

    there are so many things it could be. just start from scratch and replace the cheap basics like spark plugs, rotor, and oil. while youre in the engine compartment look at all the hoses and lines to make sure they arent cracked because it sounds kind of like a vacuum leak.

    the egr is an expensive part dont replace it unless you have atleast given the truck a tuneup first.
  10. malibuvan

    malibuvan Junior Member
    from 49424
    Messages: 7

    It may be your lock-up torque converter. It may be locking up then releasing, lock up again and then release. Check your brake switch, as the computer gets its signal through the brake switch to turn the converter on and off. If your switch is bad or intermittent it will cause this. I know this because I had the same problem on my '98 as well, although the problem was stemming from my remote starter computer that was wired into the brake circuit.
  11. BigLou80

    BigLou80 Senior Member
    Messages: 558

    I had a truck that would do that from time to time even when it was just sitting in the driveway warming up. It was a bad EGR valve dumping exhaust when the engine could not handle it at low RPM. On that truck '90-91 chevy you could move the valve with a pair of needle nose when the truck was running. so we waited for it to act up grabbed the needle nose and moved the stuck valve and the it instantly started running right. I don't recall the EGR being all that expensive at least not compared to the parts I have needed to install in my 2500HD like $750.00 mufflers and $500 transfercase encoder motors.