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s10 4.3 vortec rough idle

Discussion in 'Chevy Trucks' started by 00bluegtp, Apr 27, 2010.

  1. 00bluegtp

    00bluegtp Member
    Messages: 71

    This truck i have has a rough idle when im sitting in traffic for some time it starts to chug almost. Somtimes it wont do it at all. Very strange problem. It has a new cpi unit and lines, new fuel pump, engine only has 20k on it, It also has a newer cap and rotor that i replaced with the plugs and wires(all delco parts). What should i look for? Anyone have any ideas?
  2. creativedesigns

    creativedesigns PlowSite.com Addict
    Messages: 1,929

    Vacuum pump loose or off?

    Im pickin up an '03 S-dime this week. Gonna be a hot rod truck by the time the build is finished! 572 engine, boxed ss frame, bodydropped, black pearl with 14 clear coates with Foose spank 5lug rims! :cool:
  3. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    On the 4.3's it's caused by a partially stuck open EGR valvee. The quick fix it to use a screened EGR gasket available at most any parts store these days. It is/was a well known problem that the EGR ports from the exhaust ports up the the EGR passage in the intake would get carbon buildup in them and periodically small bits of carbon would break loose and get caught in the EGR valve, thus it can't fully close when commanded (at idle) and thus the open valve causes a rough idle. The invented screened gasket prevents the carbon from getting into the EGR.

    The correct fix is it remove the intake and clean out the exhaust passages through the intake but at a much higher cost than simply using the screened gasket deal.
  4. Mr.Markus

    Mr.Markus PlowSite Fanatic
    Messages: 5,779

    Perfect.... my wife's jimmy has had these carbon build ups for yrs. Knew what it was and how to clean but didn't know about the screened gasket. Thanks BB!!! (I call it a valvee thingy too)LOL
  5. 00bluegtp

    00bluegtp Member
    Messages: 71

    well it turned out to be a serious amount of carbon build up on the intake valves. Thry did te decarbonizing at the shop and it runs amazing.
  6. brad96z28

    brad96z28 PlowSite.com Addict
    Messages: 1,525

    serious carbon on a 20 k mile motor?
  7. 00bluegtp

    00bluegtp Member
    Messages: 71

    yea i dont understand that either. ahhh... But i drove it for 500 miles since i got it back and it was fine. Now its back to running like **** and the guy charged me $600. wtf. what could be wrong with this thing and why would it have run like a clok for 500 miles and then **** up again. It built up the carbon again?
  8. RacingZR

    RacingZR Senior Member
    from Maine
    Messages: 400

    Nice guy :eek:
  9. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    What did a $600 decarbonizing consist of? Should be details on the repair order.
  10. 00bluegtp

    00bluegtp Member
    Messages: 71

    yea three hours worth of labor and $120 for the BG induction cleaner. I live in wstchester county NY where everything is more expensive than anywhere else.
  11. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Still don't know all the details and I'm not one to point fingers but it all sounds fishy. $600 for a de-carbon? Hope that included physically removing and cleaning the intake for that cost. I also don't buy for one second that the extreme rough idle was caused by carbon buildup on the intake valves. It takes an extreme amout to grossly affect the idle and that's tough to swallow on an engine with only 20K.

    Sounds more like they cleaned the carbon blockage from the EGR (original root issue I touched on previously) and did a quick FI clean procedure (the $120 job) and down the road you went. Also bet the rough idle is back do to the same situation the first time, carbon holding the EGR valve open. The 4.3 Vortecs were notorious for it, hence the invention of the screed gasket I spoke of before.
  12. unit28

    unit28 PlowSite Fanatic
    Messages: 6,634

    Hi fellas,
    Hope i'm not being rude by posting on 00bluegtp's thread.
    What I have 93 S-10 vine code R 2.3 litre 5 spd.

    floods at start up
    poor gpm
    stutters after shifting then bogs down while accelerating, smooths out after letting up
    clatter while accelerating like it has low octane
    rough idle when sitting for awhile,
    sometimes idle will rev very high after shifting

    check engine light is operational at start up but is not staying on for codes
    I replaced plugs and wires, pcv
    I've used Lucas injector cleaner and 104 octane as per label
    will get fuel filter changed
    any suggestions for this is appreciated
  13. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    A 2.3 vin code R? Perhaps you meant 2.8?

    A fuel pressure test would be first on the list followed by checking running parameters with a scanner, checking specifically MAP readings and fuel trims.
  14. unit28

    unit28 PlowSite Fanatic
    Messages: 6,634

    yes 2.8 is what I meant to type. Thanks.
    It was cooler this moring and was a pain to get started. But when it did it was all over on trying to idle, then all of a sudden it revved up like a banshee.
    I'll find an ASE shop to help scan and test it

    Thanks again.
  15. 00bluegtp

    00bluegtp Member
    Messages: 71

    well no its not the egr cause that has a block off plate on it. It seems now that after i do the tps relearn and iac relearn at the same time it runs fine for a couple days then starts doing the same **** again. I put on a new tps and still does the same thing. I also put on a new iac... still same thing. Could this be the computer? Or even the ICM? No the labor was for checking for vac leaks. smoke testing the lines and motor to see if it had lower intake leaks wich it didn't. Labor is expensive in these parts but still not happy with his work. I will not go back to him again.
    Last edited: Jun 1, 2010
  16. unit28

    unit28 PlowSite Fanatic
    Messages: 6,634

    I finally dragged mine to the shop. It just progressed itself into heavier stutters and no gas at the injectors on starting it. I changed the map out myself and it helped with the idle until now.

    I couldn't get the fuel filter off as it was rusted together. So the shop charged me $130 for that. They did the pressure test and found it to be nothing next to zero. So here we go
    New fuel pump, sender and screen going on tonight. looking at $425 more.
    After that I still want to get a scan while it's running right?

    may you bless the mechanics and help them put my lil money maker back together in good health
  17. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    You sure do, just because there's a found problem doesn't mean there isn't more than one. It's even good practice as general PM to scan a truck occasionally even where there's immediate perceived issues or symptoms. Many times you can heed off an issue that can leave you dead in the water in the future.

    Think of it as a thorough periodic checkup. Many check the mechanicals but few even think to check the internals.
  18. unit28

    unit28 PlowSite Fanatic
    Messages: 6,634

  19. unit28

    unit28 PlowSite Fanatic
    Messages: 6,634

    well so much for that.
    Already back to sputtering bad.
    Things that are fixed is idle, start up and no more bogging down

    sputters in all gears, I thought it was also backfiring just a little between shifts
    I ran the tank low and filled it with 15 gallons of premium before I ran it today.

    I just got it from the shop yesterday and didn't run it untill today. Starting out this morning was great.
    sorry for the utube vid...I was excited..
    Last edited: Jun 9, 2010