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  1. #1

    Default 1986 code 34 problems

    1986 code 34 problem
    my engine started runing roughly the check engine light came on and code 34 showed up .Per the flow chart it seemed to run (a little) better with the MAF disconected so I replaced the MAF with a rebuilt unit from SIA Electronics via ZIP Corvette catalog. Still bad and 34 code. I then replaced the ECM with a rebuilt ECM from same co..Still bad with 34 code. I then took I to CHEV. dealer who promised a diag. and fix with their scanner. They claimed both the rebuilt MAF and ECM bad (seems unlikely). They replaced the ECM with a rebuilt Chev. ECM. but I still get 34 code.And very rough starting,idle). The SIA co. tested both their rebuilt ECM and MAF and say both are good. I replaced the MAF again with another rebuilt one and still runs rough and 34code. (per flo chart disconnecting the MAF does make code 33 which is said to mean the MAF is bad and the ECM and wiring is OK). HELP! , any ideas? what should I do next? (the local Chev. dealer doesn't inspire me with confidence )

  2. #2


    It's your MAP. I agree with your comments about Mr Goodwrench.

  3. #3


    Originally posted by Jim
    It's your MAP. I agree with your comments about Mr Goodwrench.

    Thanks but it turns out '86 does not have a MAP (most other years do) NEW INFO! the code 22 came on (TPS) and the TPS tests erratic and with too high a voltage. A new one is on order, I hope this fixes it. Thanks for the help.

  4. #4

    Default ongoing code 34 and hard starting

    No luck! Changing the TPS didn't fix any thing. So far there is a new ECM, two new MAF's, new TPS , new EGR switch. Symptom is crank engine and it starts fine then dies after about 2 sec., crank engine again and it runs about 3 sec. and dies etc.. After 5 to 10 times it barely stays running till it warms up then runs ok but with very poor gas mileage. The check engine light usually does not come on but 34 code eventially sets. Any ideas? could it be the idle air control?, pick up coil?(where is the distributor by-pass line?- the chev. manual says to try opening this line and if then runs ok it's the pick up coil) Thanks for any ideas!

  5. #5
    Technical Advisor c4c5specialist's Avatar
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    May 2001
    New Haven, Ct. USA
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    Hi there,
    There are so many bulletins for this condition in GM database that Icannot name them all, however, I will mention a few that may help you. GM dealers can access this information in SI2000.
    87-270-6e is a revised diagnostic trouble tree that gives some insight into correct diagnosis of this system. It also suggests that you check the power relay, located near the battery. This powers the MAF, and should have part number 10067925 on the top of the relay. If you do NOT have this relay, the first course of action is to replace this, no matter what else is done, this is first.
    Next, 87-650-109 is instruction on cleaning the throttle body of any excess carbon from the throttle plates, as this could also cause your 34 code.
    Finally, 87-650-119 is for a particular insight into TPS, IAC, and MAF diagnosis, and interrelation between these.
    A final thought, I am sure that you can check your grounds, and the power supply to your PCM, confirm that they are all clean and tight.
    Also, make sure to check your prom id number,and confirm with your GM parts source that this is the most current calibration, as not that this could affect your running, for maintenance.
    Please keep us posted, as to your progress, as I find this interesting.
    Besttoyou, c4c5
    GM World Class Certified Technician.
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  6. #6
    Member BigRed's Avatar
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    May 2001
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    The sypmtoms happend to me my mechanic replaced the plug in for the Dealer computer and then replaced the throttle speed sensor or something which made everything run better except the check engine light was still on but with the hook up to the dealer comp working the WHOLE computer got replaced

    I hope this helps but I also hope you dont have to replace the Computer like I did!

  7. #7


    My 86 had a similar intermittent problem. Replacing both the MAF power and burn off relays fixed it. They are inexpensive and it is recomended that they both be replaced at the same time. They are also supposed to be replaced when the MAF is replaced. I'm surprised at the lack of knowledge at your GM dealer!

  8. #8

    Default Code 34 problems


    As an owner of an 86, I just went thru a code 34 problem. I replaced the MAF, both the power relay and burn-off relay. No more 34 but now a 33.

    I checked the chip, ECM and wiring. Everything OK, but still very rough idling. I borrowed a throttle-body and replaced the existing one. Guess what, that did it. Back to normal

    Hope this helps.

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