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No high idle on start, low idle, low power

Discussion in '308/328' started by sahn44, Sep 21, 2025.

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  1. sahn44

    sahn44 Rookie

    Aug 29, 2019
    45
    New York City
    Full Name:
    M. Sahn
    #1 sahn44, Sep 21, 2025
    My 1986 328 had a 50k service earlier this spring. Shortly after that, it started behaving strangely. First, the starting wasn't as strong/quick as usual. It would take some more cranking at feel like it needs some throttle to get going. Then, there's no high idle at all, it would just idle at around 500/550 or so. Eventually it will get up to about 800 which is also lower than normal. Acceleration from stop is sluggish, at higher RPM above 3-3.5k it feels more normal but probably still less than it should.

    In the past, I had the front ignition go out due to corroded main lead and got both coils and leads replaced. That's the only repair i've ever needed in 6 years other than going in for the 50k service. I tried to feel for header heat suspecting maybe a bank was out and thought the front bank might have been too cool. So, disconnected front bank ignition to see if it made impact and car wouldn't start, then started when hooked back up. Next I thought it could be frequency valve and couldn't quite tell if it was buzzing so disconnected that and it ran terribly and cleaned up when reconnected.

    Ideas of what to look into next?
     
  2. DanielGA

    DanielGA Karting

    Mar 19, 2018
    211
    Midwest
    Full Name:
    Daniel A.
    #2 DanielGA, Sep 21, 2025
    Fuel and spark are basic checks.

    Disconnect one spark plug at a time...and see if it makes a difference.

    Fuel is harder to check. Warm-up plug could be fouled -- that would explain cold start problem; again disconnect and try? Have you, or someone removed/cleaned the injectors?
     
  3. sahn44

    sahn44 Rookie

    Aug 29, 2019
    45
    New York City
    Full Name:
    M. Sahn
    #3 sahn44, Sep 21, 2025
    You mean cold start injector? No, injectors haven't been removed/cleaned to my knowledge.
     
  4. spirot

    spirot F1 World Champ

    Dec 12, 2005
    15,232
    Atlanta
    Full Name:
    Tom Spiro
    #4 spirot, Sep 23, 2025
    My guess is from just what you are describing that you have a vacuum leak... and or a cracked wire to one of of the ignition modules... or a loose connection. my gut says vacuum leak with one of the hoses.. not connected or with a hole... or large crack. the idle is a function of the Aux Air valve, under the plenum, and then sending signals to the cold start injector etc...
     
  5. sahn44

    sahn44 Rookie

    Aug 29, 2019
    45
    New York City
    Full Name:
    M. Sahn
    #5 sahn44, Sep 27, 2025
    Visually inspected all the hoses and couldn't find any issues. Sprayed brake cleaner around hoses to look for rpm changes from a vacuum leak and nothing so far.
     
  6. TheMayor

    TheMayor Ten Time F1 World Champ
    Rossa Subscribed

    Feb 11, 2008
    107,781
    Vegas baby
    #6 TheMayor, Sep 27, 2025
    Last edited: Sep 27, 2025
    I can only tell you what happened to me and the solution turned out pretty simple.

    When I got my car it would start ok but be a bit "lumpy". It didn't miss but there was something wrong causing the engine to idle uneven, particularly when warm.

    I did a major service and replaced all the injectors, hoses, filters, and sensors. Also replaced the ignition wires with OEM and new plugs. T belts and bearings, valve adjustment, etc. What we got was a car that had a hot start problem. It would start but I had to crank more and give it a bit of gas from the pedal until it fully lit up. We checked everything including the fuel pressure and regulator. All were in spec.

    We hooked it up to a gas analyzer and found it to be running rich. Eventually, we replaced the O2 sensor and after some more adjustment, it ran great. Now either cold or hot I get an immediate fire. Without question it was black and white.

    Not sure if this will be your situation but its what happened to me. For several months now I've had zero issues.
     
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  7. sahn44

    sahn44 Rookie

    Aug 29, 2019
    45
    New York City
    Full Name:
    M. Sahn
    #7 sahn44, Nov 9, 2025 at 7:47 PM
    Update here. Took it to shop and they found oil leaking into one of the distributor caps through the camshaft seal. Said it was full of oil. They fixed that and also found the fuel accumulator was leaking and not holding pressure so replaced that. The car starts and idles well now. But, they didn't do anything for it not high idling at all. I guess shop doesn't think that's much of an issue really, but I'd like to get it working normally. My main suspect is the AAV valve is stuck in closed position so doesn't let through any aux air cold or hot.
     

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