Hello,

I own Mitsubishi Colt CZT - 1.5 Turbo.

Afaik the car is fully stock, but I cannot say if there were any modifications before that may be returned back in stock.

I own the car for about 6 months now, maybe a bit more, and just now, recently, it developed this jerking/stuttering.

Its best felt on 2nd and 3rd gears, and happens when accelerating, maintaining speed/rpm(which is exactly the RPM range where you'd be driving through town - 3rd gear 1800rpm), but also happens on deceleration - so going downhill with 3rd gear engine braking, the car will stutter.

Because its happening on deceleration, I have ruled out fuel filter and injectors issue.

I have tested for Vacuum leak, and car dies as soon as I block the main intake hole.

I tested the MAF sensor, and it does seem to be working. When unplugged, the idle went haywire, after plugging back in idle resumed normal function. Disconnecting intake after MAF causes the car to die(as MAF reports no air coming in).

I checked spark plugs - those were brand new 10k km ago. After inspecting them again, they are clean, no issues whatsoever and gap is uniform across all 4 of them. These are also expensive iridium ones.

Diagnostic tools are showing no errors at all, no misfire, nothing. Only thing I have received a few times is 420 error code, which indicates low catalytic converter performance, I do not believe it being connected, but what do I know.

I am not sure what to test next?