News

308QV Inconsistant Idle?

Discussion in 'Technical Q&A' started by Harta320, Apr 3, 2005.

  1. Harta320

    Harta320 Karting

    Nov 6, 2003
    169
    Sarasota, FL
    Full Name:
    Bill Smith
    Well, after many changes to my 83 308 qv my car's idle seems to rise anywhere from 200 to 500rpm. The changes where not to try and fix the problem but just to update the car.

    Things I have checked and changed.

    1. New injectors
    2. New manifold gaskets
    3. New hoses
    4. New spark plugs and wires
    5. Set the idle by using the throttle plate screw to get 800 rpm then turn the large bolt below the throttle body to get 1000rpm.
    6. New rubber gaskets below the intake manifold
    7. Fairly new battery
    8. Throttle cable is not catching rug or getting hung up anywhere.
    9. It is not the rpm gauge, you can here the engine rev higher.
    10. Rebuilt alternator

    I had this problem before I started all of these updates but just figured that the new injectors would probably fix the problem. The car runs great. No stumbling and revs very smoothly all the way up to 7000rpm. I plan on grounding the digi's but I think my problem might be a vacuum leak some where. If it is a vacuum leak how do you try and find it? Any other suggestions would be great.

    Bill Smith
     
  2. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Two Time F1 World Champ
    Rossa Subscribed Owner

    May 4, 2001
    28,832
    Birmingham, AL
    Full Name:
    Tommy
    I am betting it's your 02 sensor.
     
  3. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
    TN
    An 83 has no 02 sensor. 84s and 85 US specs do.
     
  4. tbakowsky

    tbakowsky F1 World Champ
    Professional Ferrari Technician Consultant

    Sep 18, 2002
    14,616
    The Cold North
    Full Name:
    Tom
    Check the o-ring under the fuel distributor. This seals the fuel head to the airflow sensor assembly. I have run accross this same thing before and I found the o-ring was dry and brittle and no longer able to keep "false air" out of the airflow meter. HTH.
     
  5. RF128706

    RF128706 Formula Junior

    Apr 8, 2004
    280
    Hi Bill,

    If I can't find a vac leak by thorough inspection of all the hoses etc. (e.g. it's a leaking flange or something) then an old trick I use is to spray the suspect area with petrol.

    If it's leaking where you spray, then the revs will momentarily change when the petrol is ingested into the intake system.

    Obviously you need to be really careful. It needs to be a small quantity sprayed each time in a relatively fine spray. Don't saturate everything in fuel (both for safety, and because it makes it harder to pin-point the leak) and no smoking.

    To give an idea, the type of spray pattern is similar to a perfume bottle spray !

    Good luck,

    RF.
     
  6. Rifledriver

    Rifledriver Two Time F1 World Champ

    Apr 29, 2004
    25,491
    Austin TX
    Full Name:
    Brian Crall
    You need to be sure that the EGR valve is not sticking open, disconnect the pipe at the air flow housing and plug it to see if the idle quality or speed changes. Also you need to set idle by putting a vacuum gauge on the port for the EGR and adjusting the throttle stop screw to less than 1 1/2 inches of vacuum and then using the idle air bleed to establish proper idle speed. If this is not set correctly you will be opening the EGR at idle and it will never idle correctly. Also make certain you have slack in the throttle cable and that all passages in the throttle housing are clean.
     
  7. Harta320

    Harta320 Karting

    Nov 6, 2003
    169
    Sarasota, FL
    Full Name:
    Bill Smith
    Thanks for all of the ideas.

    TBowsky, How hard is it to replace that gasket on the fuel distributor. Is it something I can do or should I get someone who knows what there doing?

    Rifledriver, forgive me for asking a dumb question but which valve is the EGR valve. Is that the one directly off of the throttle body with 2 small hoses connected to it?

    I will let keep everyone updated.

    Bill Smith
     
  8. Darolls

    Darolls F1 Veteran
    BANNED

    Jul 2, 2003
    6,799
    Full Name:
    Sparky
    Use a spray can of carb. cleaner instead.

    Available at your local auto parts store.
     
  9. RF128706

    RF128706 Formula Junior

    Apr 8, 2004
    280
    Good point, I have used carb cleaner and also "easy-start", these have the same effect, but I wouldn't suggest you use it on a catalyst equipped car just in case of cat contamination. I'm not too sure what stuff is in carb cleaner.
     
  10. Darolls

    Darolls F1 Veteran
    BANNED

    Jul 2, 2003
    6,799
    Full Name:
    Sparky
    A carb cleaner such as 'Gumout', won't harm cats or oxygen sensors. It doesn't contain Methanol or Methylene Chloride.
     
  11. geekstreet

    geekstreet Karting

    Feb 7, 2005
    220
    Sydney
    Full Name:
    Cam
    What's the frequency of the rpm variation? Does it go up & down & hunt around say every few seconds, or it is it a faster idle sometimes & slower at others (eg next traffic light, next day)?

    If the former, this is easier to debug. Try pulling one a plug at a time, leaving the other 7 running. This will obviously affect the idling smoothness & speed but you're looking to see it is stops the "hunting". If pulling a particular cylinder or 2 gives you a more constant (rough!) speed then you can look at injectors, plugs, etc for those cyls.

    If all plugs have the same effect then it's a "global" influence such as vacuum, electronics, etc. Good luck.
     
  12. Harta320

    Harta320 Karting

    Nov 6, 2003
    169
    Sarasota, FL
    Full Name:
    Bill Smith
    First, thanks for all of the suggestions.

    I finally got my car back together and sent it to a shop in Sarasota (Grand Turismo) for final alignment and various other items I could not do. Fuel distibutor settings being one of them. Ends up my fuel distributor needs to be rebuilt. It works ok now but a few cylinders are running a little to rich and cannot be adjusted correctly for a good smooth idle. If anyone on the west coast of FL needs a good shop the guys at Grand Turismo are fantastic!

    Bill Smith
     

Share This Page