308 QV Cold High Idle

Discussion in '308/328' started by teatime, Sep 24, 2011.

  1. teatime

    teatime Rookie

    Mar 8, 2009
    NW Burbs, Chicago
    Full Name:
    Todd A.
    I was hoping to get some thoughts around my high idle issues on a cold start. My car is a 1984 308 QV US version.

    I just had a new Cat installed (Fabspeed) and now my car jumps up to ~2,800RPM on a cold start and stays there until I blip the throttle after about 7 mins. It then comes down to ~1000 RPM. Before I had the new Cat put on, the cold start seemed to work normal. Cold start would go to ~2,000 and then ON ITS OWN, would drop to ~1,000 after warm up (5-7 mins)

    Now it just stays high @2,800, and I have to blip the throttle to get the RPMs to come down. After almost 10 mins it still will not come down and the temp on the water gauge jumps up to 195 & past after just 7 mins!.... I called the mechanic who put tha new Cat on to ask about this. Turns out he jumped the temp swtich on the coolant expansion tank, and told me that he found the switch to be bad. He said jumping this switch should solve it. I didn't like the idea of having wires jumped, so I bought a new coolant expansion tank temp switch from Ricambi and installed it and hooked up the wires. I have noticed no change (jumped vs non-jumped) in this high idle behavior.

    Any thoughts, I'm thinking a vaccum hose leak somewhere but wondering if anyone else has encountered this. I did try searching and couldn't find a similar issue.

    Basically I just want the car to high idle up to 2,000 anf then come down on its own like it did before.

    A side note, before I had the new Cat installed, the mechanic said my car was super rich(6%), he says he adjusted the fuel mixture and now with the new Cat and adjustment he says it is back to normal. I have no way of telling for sure, but I can confirm the really bad rich smell is gone. Not sure if his adjustment of this fuel mixture has an impact on idle speed.

    Thanks in advance...

  2. Neonzapper

    Neonzapper F1 Rookie

    Oct 19, 2008
    Full Name:
    I'm not sure about your car. I have an '83 QV which idles the same on start-up in any weather. Perhaps it is because the car is garaged? When downshifting at high speeds, the Borla exhaust gurgling is prominent. My mechanic tells me it is unmixed fuel and normal. I have no cats (Maryland Historic, so they were removed).
  3. Paul_308

    Paul_308 Formula 3

    Mar 12, 2004
    The AAV bypasses air around the throttle plate, controlling idle speed. And it has it's own internal cold/hot control. However, US cars have 2 additional components added to them to add even more air, raising the cold idle rpm much higher. Cold idle spec for US cars is actually 2800 rpm.

    For a general understanding and diagrams, read this article. Also know the coolant temperature switch also controls more circuits than cold idle speed and shouldn't be altered, otherwise the life of your new cats can be reduced.

    Reducing cold idle speed on US spec cars:
    1) Place a restriction in the large tubing which the air valve controls. (Don't confuse this device with the AAV.) This way you can achieve a cold idle speed of 1800 rpm or sum-such depending how much air the restriction cuts off.

    2) Or reroute the vacuum lines from the cold idle electrovalve to the air valve so the air valve is always pulled shut by the vacuum. It works for me.

  4. teatime

    teatime Rookie

    Mar 8, 2009
    NW Burbs, Chicago
    Full Name:
    Todd A.
    Thank you, I appreciate the messages.
  5. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    Full Name:
    Steve Magnusson
    #5 Steve Magnusson, Sep 24, 2011
    Last edited: Sep 24, 2011
    '83 (K-Jet without Lambda) and '84-'85 (K-Jet with Lambda) US 308QV are different in this regard:

    '83 has the AAV and the cold star air valve that Paul mentioned, and the stock cold idle is quite high -- like 2800 RPM.

    '84-'85 only have the AAV so the cold idle shouldn't be so high.

    Easiest test for you would be to physically "pinch" one of the large air lines going to-from the AAV closed during your unusual high cold idle (simulating a fully closed AAV). If the cold RPM comes down a bunch, the AAV would be suspect (open too much when cold and not closing soon/smoothly enough); if the cold idle stays high, you've got some other problem, or, as fastradio has previously observed many times, it's multitude of adjustments are just not tweaked up properly ;).

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