Initially thought that this was related to some water in the tank, since it started when the gas dropped to 1 bar (already put some stuff HEET when put the whole tank, did 60miles so far). ODB throws out multiple cylinder missfire (codes 300, 301, 302, 303 etc). It last up to 3 seconds. Sometimes the check engine pops up sometimes it doesnt. there was absolutely no problem under load. does it seem like a fairly common problem ? Intake manifold clogged ?
Yes and yes. There are YouTube videos on how to clean the transfer pipe. It's not too bad of a job if you are moderately, mechanically inclined.
there is this assemly mounted on EGR switch, both screws seems to be stuck/rust. any trick to loosen them ?
Those are probably SS bolts with a shouldered cap that retains the torque in conditions of expanding and contraction. First of all, use a proper socket or wrench to avoid rounding the head of the bolt. Then you need to use a snapping blow to the tool to break it loose. As with any exhaust related fasteners, you always run the chance of snapping the bolt off. Good luck
I thought I would make a small follow up. Initially it was a common gen3 problem, cold, rough start, for couple seconds, small hesitation. for some reason, I decided to put in 1$ gas treatment. Well, hell descended upon me - rough start, drive, acceleration. It took 4 full tanks to get that out. In the meantime I was so desperate that I cleaned that EGR pipe and put some WD40 to EGR valve body (no immediate effect). After almost a month it slowly came back to normal, and no more rough start! I got my power back...first 2 months and 5500miles. Im not sure what helped.
These Atkinson Cycle engines evidently don't like snake oil. How many miles are on your car? There is an extended warranty on the intake system that you might look into.
to my surprise, there was maybe 2mm buildup, completely dry. I got the check engine with the typical random cylinder misfire. Havent reset that engine light yet.
At 150 k miles, what intake maintenance has been done ( pcv, throttle body, MAF, intake manifold cleaning, etc)? Does it consume oil?
