Hey, have this problem that i can't seem to figure out...

Couple years ago when I changed my radiator to a mishimoto, I found that sometimes on mornings even if it's fully warmed up, when I first go into boost, the car gives a bad hesitation and stuttering: sometimes with a puff of white smoke (I think) and sometimes with the idle being rough for a few seconds...

It will do this once or twice, then it will boost normally right up to redline... sometimes may have a slight hesitation if any. It's more pronounced if i don't drive the car for a few days or if it's been raining the night before and most of the day. After that, it runs fine all day.

What I can't figure out, is why. If the night before and next day is warm, it doesn't do it. I could be driving out of boost for a couple hours well after first start on a rainy day and once I go into boost it stutters and hesitates badly for that couple times, then it's good.

I have no loss of coolant, no oil/water mixing, changed plugs and even the cam sensor, changed vacum lines and checked for boost leaks, coilpacks and sensors were all in spec etc and nothing changed it.

Could changing the radiator somehow cause it to be "too cold" for initial full boost? Is there a parameter in the ECU that could cause this?

 

My E4 is doing the exact same thing. As soon as it goes on boost it starts stutering. I changed the plugs and still the same. I am leaning towards boost leak or bad coils. it was running very rich and there was a pretty big flame out the back one time before it got really bad with the hesitation.

Any ideas suggestions?