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Communities > Diagnostics > USA Cars > 2008 Chevy Malibu - Stumbles on Takeoff
2008 Chevy Malibu - Stumbles on Takeoff

860 Views 0 Replies Create Time: 2021-10-12 17:52:00

  •   Level 2   
    (23) points
    Josh Mucinski
    2021-10-12 17:52:00
    Car: 2008 Chevy Malibu 3.6L (190k miles)
    Scan Tool: MX808 (Up to date)

    Short Problem Statement: When accelerating (both on take off, and accelerating on the street/ highway) will stumble. Has high idle (900 RPM) with and without AC off/on.

    Long Problem Statement: When I take off from a stop or accelerating on the highway. Every now and then the car will stumble. Typically happens between 2k and 3.5k rpm. No check engine light and no other codes showing for the PCM or TCM. There are couple of codes for the remote locking system and body control module, dont know the codes right now, but seems like it has nothing to do with this. So with my 808 i looked at the short and long term fuel trims, MAF, TPS, and O2 (both up and down stream ones). Short term look, less than 5 either way. but long terms are close to -15 (negative 15). MAF looks ok. 4.6 g/s at 900 rpm idle, changes with increase as well. I pull the MAF to see what the car would do, still high idle. TPS looks good, no dead spots that i could see, will have to look closer and test again. The car also has what i think is a high idle, car is 900ish and desired from the PCM is 900 as well. At times i have seen the car idle around 600 rpm and be fine, not sure why the car is idling at 900 and the pcm is telling to idle at 900 either.

    Any one have any ideas or similar issues

    Fixed Items:
    -Cleaned Throttle Body
    -Cleaned PCV and did the mod
    -Changed Air filter (it needed a new one anyways)
    -Changed out Front top O2 Sensor (one from the junk yard, no change)
    -Ran Fuel System Cleaner in a full tank of gas
    -Plugs Awhile ago (less than 30k miles ago)
    -Transmission Rebuilt (1k ago) (was happening before rebuild)

    Items to do yet
    -Injector leak down test
    -Track down the negative long term trim issue
    -High desired idle (900 rpm)
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