2006 GT / Manual
125K miles
Series of events:
1) engine light comes on one day and start to notice symptoms (which I have a hard time describing).
-- Basically, the moment I touch the gas the engine feels rough for a moment before revving up. It's like the engine 'flutters' or hesitates before revving up.
-- It is always present when the engine is cold. It is completely gone or extremely minimized when the engine is warm.
-- I primarily drive the car on the highway ~15 miles to and from work. There's no noticeable problem at highway speeds and by the time I get to work usually the problem is completely gone.
2) Take car to autozone to pull the code quick: P2004 (Intake Manifold Runner Control (IMRC) Stuck Open (Bank 1))
3) 1-2 days later the engine light goes OFF but symptoms remain.
4) Roll with it for a few weeks before taking it to a mechanic since the situation is persisting (but not any worse). I tell them all of the above about how the light was on, the code, and how it went off.
5) Mechanic checks computer and sends me this:
"p0316 Engine misfire detected on start up. P0689 PCM power relay sense circuit low.. There is history of misfires on cylinder #2 in the data. Removed spark plug and found it worn. Recommend replacing plugs and coils."
6) I ask them to pull a second plug - they pull 2 others - they all look old and corroded.
7) I tell them to replace all of them + coils. $1200
8) Get car back and... rough running still there. Not fixed. Exactly the same.

Now, I can see how they get from P0316 to "replace spark plugs" - especially in their state, BUT, the plugs were working. The car drove down the road just fine. (and going out on a limb here, a misfire or two at startup doesn't sound like the end of the world - the car, and those plugs, had a lot of miles on them).

It seems to me they completely disregarded what I told them about the engine light coming on and pulling P2004.

It seems way more likely to me that an entire bank's butterfly flaps not functioning well would cause this rough running. But I'm no mechanic.

As an aside, they only drove the car minimally because (and I'm not making this up) the driver's set is stuck in the furthest back position and their mechanic didn't feel safe driving it. That is, they were too short to reach the pedals safely.

It seems to me like a complete mis-diagnosis.

What would you do?

 

I would pull the intake off myself and check the charge motion flaps and see if there is a lot of build-up there preventing normal operation. They tend to sometimes get stuck. Before the supercharger install, I did that and removed those plates and put the deletes on and as I had a Brenspeed tune, I had them adjust my tune for that and it ran just fine. Mind you I had no problems prior.