So last week, I took my car ('09 Matrix, 75K miles, bought new) in to the dealer because there was a recall out on the computer - apparently it would still gun the engine if you were to push both the brake and gas pedals at the same time. The fix was a software patch that would prevent that from happening.
Anyway, I get the car back and it starts shaking for about 2 minutes, whether it was idling or moving. I didn’t think much of it because it went away and nothing happened for about a week. Sunday, the car shudders for a few seconds and the check engine light comes on. I check online and it says that for an '09 Matrix, the most common cause is the gas cap not being tightened all the way. I give it a shot, and voila, it goes away for 2 days. Yesterday, the shudders for about 20 seconds (it starts when idling, but continued for a few seconds after I started moving), and the check engine light came on. This time, fiddling the gas cap didn’t cause it go away.
When I had the car in for the recall, they did the whole “free 25-point inspection” bit and the only item of note was that the transmission fluid was starting to change color. My car hasn’t ever had to have any maintenance work done on it (besides the standard service interval).
So I guess my main question is: what’s the cause of this happening, and was it related to the recall fix?
Also, side question: when they said that the transmission fluid was changing color, they also said that my car required a full flush (for only $400+ dollars). Normally I’d be skeptical, but this was a Toyota dealership service department. Are they BS-ing me?