My 05 MCS engine (4200 miles) is shaking, stalling, missing. It stalled out several times on the road, and it was hard to restart. Before stalling out, the SES light blinked for a few seconds, a couple of different times. It was bad. The car isn't driveable. It was transported to a dealer. The exhaust smells rich to some folks. But, I've been told that the car might behave the same if it were running lean.

Up to now, the car has always run smoothly and strongly. The problem appeared with no prior warning when accelerating into a left turn out of a restaurant parking lot. The car had been sitting for an hour before that. I had filled it with gas 45 mins - about 40 miles - before that. The car started normally and drove normally for a few feet to the road. Then, cough, cough!, spit, shake, stall when I stepped on the throttle.

The dealer has checked plugs, throttle body, sensors (map, O2, maybe others), header and cat, error codes (there was one code, I don't remember what it was), maybe pulley, maybe other things too. So far, they think that everything has checked out okay. They haven't yet checked the head, engine management software, cold air intake, injectors, fuel or fuel tank and filter. They haven't figured out the cause of the problem yet.

What's happening? What should the dealer be checking? BTW, I'm not unhappy with the dealer. I'm trying to help the dealer by tapping the fantastic pool of experience and skill within NAM's members. This seems to be a tough problem.

 

Bad gas? That's my guess.

Life was good before that fill-up. Chances are, if you can make it through that tank, your life can be good again. I think there are additives that can counteract water in the fuel, if that's what the problem is. Keep us posted.

 

This is going to take a good old-fashioned mechanic to sort out, not just one of these guys that knows how to read codes. My first two guesses would be bad gas (as has already been posted) or a sticking EGR valve. Third guess would be a faulty or dirty Idle Control Valve.

 

Your problem sounds pretty severe, but unfortunately there is no tell until you take it back to the dealer for a full check up.

Could this be bad gas? Sure. ECU software problem? No doubt. Defective engine wiring harness or throttle body control module? Quite possibly.

Take it back. That's what your warranty is for.

 

I think the biggest problem is your dealer! I don't see how this is not readable when they plug it in. Even if it's what was mentioned above, the memory should tell them exactly what was going on, and they should be able to sort it out from there. They should be able to even tell you the date and time you experienced this problem. No?

 

I had the same problem all though not as severe. I would start my car and it would run for like a minute them the revs would drop and eventually it would stall. I would start it again and it would stall right away, it kept repeating this process every once and awhile but the car is fine now. I believe the problem that I had was bad gas.

 

Here's the answer. It was a bad cam bearing cap and bad cam gear, and consequentially, truly lousy timing.

What a surprise.

I picked up the car yesterday and drove it for three hours, on the Interstate and on back roads, fast and slow. It's running great again. Woo hoo!