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Thread: PO302 Cold start issues and stalling

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    Question PO302 Cold start issues and stalling

    I have posted this on another Fiat 500 forum, but it hasn't received much attention and I am hoping there is someone here that can help.

    I have a 2012 500 NA that I purchased this fall with 82K. Since the cold MN weather has set in, I have been receiving terrible cold starts – misfiring, idle all over the place and eventual stalling. The ECU has thrown a couple different misfire codes, the most common being PO302 cylinder 2 misfire and occasionally a PO300 multiple cylinder misfire code.

    Once the car is up and running after the initial cold start issue, all symptoms disappear and the car drives beautifully. I’ve let it sit a few hours and the startup is normal. Sitting longer than 8 hours in this weather tends to bring back the cold start issues. It is hit or miss if I get the cold start after sitting outside at work for 7-9 hours. This is not a primary vehicle, so I have been driving it once a week since these conditions have started occurring.

    The previous owner had the following services performed within the past 2,000 miles, a coil pack was replaced, 4 new spark plugs, engine oil flush and change. I noticed the oil change receipt indicated that they put 0W40 synthetic oil and the cap indicates 5W30 should be used.

    Is there any chance the oil weight would be affecting the cold start? I know the multiair system is driven by the oil pressure.

    My thought is that it is somehow related to the ECU programing that runs the engine rich at cold start to get the engine up to temp. If it were a bad plug/coil etc, I would anticipate having issues beyond the cold start - specifically at WOT.

    I know there's a TSB related to cold start issues, but when I read though it the symptoms are not the same.

    The nearest Fiat dealer is 150 miles away and I usually avoid dealerships when it comes to maintenance and repairs.
    Last edited by FrankieBeats; 02-08-2018 at 09:27 AM.

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    It's always difficult to troubleshoot textually, but here are a couple thoughts:

    Yes the Fiat Multiair system relies on oil to run the intake valve system. There have been known issues when either engine oil pressure runs low due to deferred maintenance, or running the incorrect viscosity oil. I would definitely start by changing to the correct viscosity oil.

    The number two cylinder misfire may or may not be related to the Multi Air valve system. I would do a cylinder leak-down test on the #2 cylinder. There have been instances (my wife's car as an example) where 2012-2013 NA 500s have had burned #2 exhaust valves. The symptom of that is similar to what you're describing, where you start getting a combination of specific #2 misfires with some random misfire codes. The symptoms get worse, where eventually the #2 won't fire at idle. Hopefully that isn't the case with your car, and maybe just an oil change will help, but thought it would be worth mentioning.
    Last edited by KellyfromVA; 02-08-2018 at 09:47 AM.

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  4. #3
    Like Kelly said go to the basics like the correct oil weight. No need to flush the engine like the previous owner did and probably not a great idea anyway as it could push gunk into the MultiAir filter/ unit. As you get a misfire on cylinder 2, try moving the coil to another cylinder and see if the misfire follows. Also, because you don't know the quality of the mechanical work performed by the previous owner, check the spark plugs to make sure they are the proper, OEM ones and have been gapped correctly.

    As it sounds temperature dependent, you may want to check the temperature sensor to make sure it is reading correctly.

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    Quote Originally Posted by Fiat500USA View Post
    Like Kelly said go to the basics like the correct oil weight. No need to flush the engine like the previous owner did and probably not a great idea anyway as it could push gunk into the MultiAir filter/ unit. As you get a misfire on cylinder 2, try moving the coil to another cylinder and see if the misfire follows. Also, because you don't know the quality of the mechanical work performed by the previous owner, check the spark plugs to make sure they are the proper, OEM ones and have been gapped correctly.

    As it sounds temperature dependent, you may want to check the temperature sensor to make sure it is reading correctly.

    Thanks for the advice. The work performed on the vehicle prior to my ownership was done at a reputable shop that specializes in European vehicles. They specify on the receipt that they put a "Fiat" oil filter on, but then went with the 0W40. I will change it out for 5W30 and give the coil swap a try to see if the code follows the coil. Any idea where the temp sensor is located?

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    How old is the BATTERY?

    Believe it or not, a battery that is strong enough to start the engine on these may not be strong enough to provide for a smooth idle or even to prevent the engine from stalling when under load in cold temps.

    FWIW I'm fighting a very similar issue on my Abarth. P0302 sometimes, and then stalling when I clutch in and it dips to idle. Only does it for about the first 20 minutes of the day.
    Last edited by aelfwyne; 02-11-2018 at 05:36 PM.
    2015 Rosso Abarth
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    "Most of Alvin's Parts are on Other People's Cars" - NGEN

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    Quote Originally Posted by aelfwyne View Post
    How old is the BATTERY?

    Believe it or not, a battery that is strong enough to start the engine on these may not be strong enough to provide for a smooth idle or even to prevent the engine from stalling when under load in cold temps.

    FWIW I'm fighting a very similar issue on my Abarth. P0302 sometimes, and then stalling when I clutch in and it dips to idle. Only does it for about the first 20 minutes of the day.
    Thanks for the response.

    The battery, alternator, and starter were all replaced in November right after purchasing the vehicle.

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    Senior Member aelfwyne's Avatar
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    Well is you find a solution post back here. I don't feel I have mine solved yet.
    2015 Rosso Abarth
    - HEAVILY MODDED - Eurodrive Ph.2

    "Most of Alvin's Parts are on Other People's Cars" - NGEN

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