[Liam2011]

Our 2011 Passion coupe has 71,000 miles, and for the last 4,000 or so it has suffered frequent (2-3 times/week) engine-limp mode--most often when cold. So far it is always cured with a park/restart, and usually a single restart fixes it. Engine light has been on the whole time. Pitiful excuse for a dealer (Mercedes-Benz of Ann Arbor MI) unable to diagnose/rectify the problem; just put new plugs in, reset the MIL, and experienced no misfires on their "test drive" so gave it back to us. Here's what we know from generic scan tool and parts-store borrowed tools:

Codes: P0300, P0301, P302, P303, P0455.

Don't care about the last one, and somewhat wonder if the gas cap is just bad, because we've tightened the bejeebers out of it.
Apparently we're getting occasional misfires in each cylinder. The battery tests perfectly fine, so that's out too. I really don't want to contemplate "low compression" but I suppose I can run some Marvel Mystery Oil or whatever and see if that helps. I am trying to track whether one cylinder misfires more than another. Then:

A) Maybe invest in a coil-pack for that one, then see if it never misfires again.
B) Contemplate fuel injectors? (Or hope for a Marvel Mystery Oil miracle here too?)

Anything I'm missing? In limp mode the transmission still always uses all gears, so I'm ruling out transmission clutch/shift-motor issues. We don't get the triangle lamp either, so I'm inclined against reluctor rings as a culprit.

Also, anyone know of an independent in Southeast Michigan who works on smart cars? We can't even find an alignment rack anywhere that can fit the fortwo (including the dealer).

 

[jwight]

Sounds like at least one cylinder misfiring. If it's the dreaded burned valve issue, there's no fix except reworking or replacing the cylinder head.

 

[Liam2011]

Runs perfectly fine, totally peppy until the limp happens. And 71,000 miles is pitiful durability if valves are burnt. It was owned by two different women who had full service history too, so I don't suspect abuse in its previous lives. Surely this is some electrical or fuel issue.

 

[MB DNA]

Burnt valves on a smart are not necessarily miles driven?

Any aftermarket options - Cruise Control or GoPedal???

 

[Liam2011]

Nope, it's all bone-stock. And wouldn't burned valves run kind of rough in between limp events?

 

[jwight]

YMMV, but our 2011 went through this around the 34K miles mark. Tried Seafoam, resetting the trouble code, etc. and while the CEL kept coming back the car drove fine, including a couple of road trips, with normal gas mileage. Only in really cold weather would it run rough....