Why does my 2012–2019 Fiat 500 misfire, especially on a cold start?

Short answer: The Fiat 500's 1.4 engine uses a MultiAir actuator (owners call it the "brick"), an oil-powered unit that opens the intake valves. When it starts failing, you get misfires and rough running, often on cold starts. Check the oil level and plugs and coils first, because the actuator is expensive.

Symptom: Rough idle or shaking on a cold start, a flashing or steady check-engine light with misfire codes, or a misfire at low speed that clears up once warm.

What to check first

1. Check the oil level and make sure it's the correct oil. The MultiAir unit runs on engine oil, and owners point to low or wrong oil as a trigger.
2. Read the codes. Misfire codes like P0302 (cylinder 2) are common.
3. Swap ignition coils between cylinders and see if the misfire follows the coil. Check the spark plugs too.
4. If plugs and coils are fine, have a shop test the MultiAir actuator before you buy one.

Likely causes

1. Spark plugs or ignition coils. The cheap stuff to rule out first.
2. Low or wrong engine oil. Can upset the MultiAir unit.
3. Failing MultiAir actuator ("brick"). The big one. Owner-reported quotes are in the cost section.

What it usually costs

Owners report MultiAir actuator quotes well into four figures. One r/abarth owner was quoted about 2,100 dollars for the part plus about 1,600 dollars labor; another posted about 1,400 dollars for the part and 1,100 dollars to install; and a Fiat 500 USA Forum thread is titled after a 1,700 dollar actuator job. Prices vary a lot, so get more than one quote.

Is it safe to keep driving?

A steady light with a mild misfire can be driven gently to a shop. If the check-engine light is flashing, the car shakes badly, or it loses power, don't drive it. A heavy misfire can damage the catalytic converter.

DIY or shop?

Oil, plugs and coils are DIY. The actuator is DIY for experienced owners only; most owners have a shop do it.

Recalls, bulletins and complaints in plain words

• No recall covers MultiAir misfires in NHTSA's list. Fiat 500 recalls on file cover other things, like a manual-transmission clutch spring and an automatic shifter cable bushing, so check your VIN.
• NHTSA complaints: 110 of 810 Fiat 500 complaints from 2012–2019 mention misfire, MultiAir, rough running or stalling.

What owners report

• A Fiat 500 USA Forum owner had a MultiAir "brick" failure and asked what to do next.
• A Fiat 500 Owners thread covers misfires on startup with MultiAir-related codes.
• A 2012 Sport owner on Fiat 500 USA Forum chased an intermittent cylinder 2 misfire.
• An r/abarth owner asked for advice on a MultiAir actuator quote, and another r/abarth owner asked if their actuator quote was fair.

My take

My advice as a former finance manager: on a used Fiat 500 the MultiAir unit can cost a big chunk of what the car is worth. Start it cold before you buy, and walk away from one that shakes on startup unless the price reflects it.

Vehicle focus: 2012–2019 Fiat 500 and 500 Abarth with the 1.4L MultiAir engine.

Safety / mechanic note

A flashing check-engine light means stop driving and get it checked. Verify with a mechanic.