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Idle Adjustment

Discussion in 'Truck & Equipment Repair' started by Daddy Wags, Sep 24, 2007.

  1. Daddy Wags

    Daddy Wags Member
    Messages: 62

    I have an '89 Chevy K2500 350 CID. I just tuned up the engine, but need to bump up the idle a little. I think it's set from the factory (stupid). Is there anything I can do?
     
  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Was the idle too low before you did the tune up or did the tune up affect the idle speed? What all did the tune up consist of?
     
  3. Daddy Wags

    Daddy Wags Member
    Messages: 62

    No it wasn't. The timing was off quite a bit. Plugs,Wires,Cap,Rotor,PCV Valve,Air Filter,Fuel Filter.
     
  4. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    The timing is what probably affected your idle setting then...what was the exact procedure you used while setting the timing? Did you disconnect the timing connector plug near the firewall before you set the timing? If not, then the timing will be way too far ******** which will slow the idle way down.
     
  5. sweetk30

    sweetk30 PlowSite.com Addict
    Messages: 1,588

    if you realy need to set idel. its not a simple set thing. the tbi unit and computer need to be done a certion way.
     
  6. Daddy Wags

    Daddy Wags Member
    Messages: 62

    I did unplug the wire while the truck was off. Then started it and set timing, shut off engine and reconnected wire.
     
  7. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Did the truck idle even slower after you disconnected the timing wire and then started it, or didn't disconnecting the wire seem to affect the idle speed any?
     
  8. Daddy Wags

    Daddy Wags Member
    Messages: 62

    Yes, the idle was definitely lower after I unplugged the wire.
     
  9. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Ok, that tells me that you got the correct wire and that the ECM is controlling the timing like it should be. The only other reason the I can see that you could have affected the idle speed by changing the timing is if you incorrectly read the timing marks on the tab or balancer.
     
  10. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    Does a TBI system have like an Idle Air Control Module? Like the newer systems?
    It feeds air to the system for the idle, it closes when ignition's turned off. Or maybe something to pull the throttle open a little for the idle that may need adjustment or cleaning / lubed.
    Make sure the timing's right. If the trucks kind of new to you the old owner may have set the timing to correct the idle. The harmonic balancer may of turned on the shaft and changed the location of the marks. My Ford has rubber between the two parts and they will move when it gets rusted. Does it have a threaded throttle stop on the throttle linkage with no way to turn it? I took a drimel with a fine cut off wheel and cut a slot in the screw on the opposite end so I could adjust the idle speed.
     
  11. sweetk30

    sweetk30 PlowSite.com Addict
    Messages: 1,588

    like i said before its a big prossess. and if not familer with it. you can screew stuff up. but yes there is a iac=idle air control on a tbi unit. and i could dig up the steps to reset its position. you should never need to mess with the sealed cap on the base idle set screw. that would be opening a can of worms:dizzy:
     
  12. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    It's an old tired truck I needed to get just a little more idle speed out of it. Tired injectors everything else is newer.
     
  13. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    OK, couple more things here...

    You originally said that it needed bumped up "just a bit". What RPM is it at now and what was it idling at before you did the tune up and timing adjustment?

    You also mentioned that this low idle problem didn't occure until you set the timing and did the tune up. What did you set the timing at?

    And, since the tune up/timing adjustment affected the idle speed, I wouldn't be too quick to try and reset the idle speed. If it was OK before the tune up, why would you need to change it afterwards? You shouldn't have too...
     
  14. Daddy Wags

    Daddy Wags Member
    Messages: 62

    I don't have a tach, so I don't know what it idles at in gear. I've read to set the timing @ 0. I can't read the #'s on the tab, but my mechanic said to use the middle point on the metal tab for 0. There's 3 points on the tab that point towards the front of the truck. I don't want to mess with trying to reset the idle. It's not worth it. I just hope that middle mark is the correct one.
     
  15. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    I can't remember from memery where zero is on the tab but every "point" on the tab is 4 deg. Would it make it possible to read the tab if you scraped it with a wire brush or sand paper? Or is it like most of the tabs on an older truck...barely hanging on there?:D Also, have you driven the truck much since you changed the timing and cleared the code (from having the timing wire disconnected) for the ECM? Some of the TBI trucks are extremely slow to "relearn" their operating parameters after a major adjustment or a battery disconnect.
     
    Last edited: Sep 29, 2007
  16. Daddy Wags

    Daddy Wags Member
    Messages: 62

    I tried sanding the tab, but still can't read. The tab is solid, but not legible. I've been driving the truck alot. It has good power, better than before. When I plugged the timing wire back in, the check engine light went off on the dash. I didn't have to disconnect the battery.
     
  17. sweetk30

    sweetk30 PlowSite.com Addict
    Messages: 1,588

    every spot is 2* on gm.

    and take a fine pick and gouge around and the top dead center will be a front to back grove in the ballencer. clean it out and use tire chalk or paint pen and fill it in so you can see it. then set to 0*
     
  18. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Every "spot" as your calling them is 2 deg, but every forward facing "point" from one to the next one is 4 deg.
     
  19. Daddy Wags

    Daddy Wags Member
    Messages: 62

    So, is the middle of the 3 "points 0 deg?
     
  20. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    On the TBI 454's it could be, but I can't recall from memery...sorry. I know on the small block's it isn't, as most of them have 5 or 6 "points", not just 3, that go all the way from -4 deg to +10 or +12 deg. I'll have to look at the next 454 TBI truck I see to refresh my memory. If the truck runs good and has good power I wouldn't worry too much about it although if you want you can bump the timing up just a bit. It will add a little more power and throttle response