I have a 2003 S40 1.9T which i got for a steal 1,400$ one owner 84k miles and perfect inside out, the only problem im having is when i hit the gas (automatic trans) at about 2500rpms I get this stutter its feels like somthing holding it back and the car trying to push thru the stutter and when i push harder on the gas i get a flashing CEL so i try not to do that. I put it on the computer and got the code that i had a misfire and coil was bad. Replaced all the coils (2) and still same problem. Now i thought it could be somthing with the turbo, so i disconnected the rod that runs from the waste gate to the exaust. I cant think of the damn right name for the parts right now, but its the rod that runs from the wastegate and goes over the top of a hindge type that moves from left to right to open and close a valve by the exahust right by the engine block.. When i did this and had no turbo running i had no stutter or any problem with my engine. It ran like a new 4cyl without a turbo. SO now my problem is what the hell is going on. I checked all the hoses for the turbo and the intercooler and everything is ok. I still have the stutter. ANYONE GIVE ME SOME ADVICE.

Thanks

 

did you also replace the plugs? I avoid expensive premium plugs as I've found my S40 runs nicely on OEM or copper core (old school plugs). The other issue common to the s40s is the connectors to the coils. Look for cracks and corrosion - I bet your wire looms have all disintegrated too right? After that, check for any vacuum line issues - cracked hoses or caps, broken tees and then check the MAF to turbo to intercooler to throttle body tubing - you may need to spray around with some carb cleaner to see if something gets sucked in. Any problems starting the car - cold or warm? Another possible cause of misfires is fuel pressure issues, so you may need to test that as well.

 

Installed a new fuel pressure regulator all the hoses so far look good and the plugs were changed just a few hundred miles ago all good. Ill check the connectors to the coils, they looked decent to me be i really didnt look to close. thanks for the info i check back later when i check everything else. Didnt think about the MAF for the Turbo thanks

 

Did you also replace the wires with the coils? Each time I've experienced the symptoms you describe it was either a spark plug, or a coil or a spark plug connector (plastic part that fits down over the spark plug on the other 2 cylinders). They get these hairline cracks that allows the spark to jump to the head when you get into boost. The reason it misfires under boost is that it's easier for the spark to jump to the head rather than across the spark plug gap. That is why turbo engines need a closer gap versus a non-turbo engine. (typically .028 vs .040 or larger)

As an experiment you can try covering the lower part of the connector in something like RTV to see if the problem goes away.