working on an L32 3.4L MPFI early 90s style in an F body

the owner very recently assembled the engine completely from scratch and everything is brand new in it.

i am unsure whats stock and whats not inside but externally it is bone stock. no mods to the throttle assembly or to the injectors or ignition etc.

when you fire it up it runs real strong almost like its lopey and modified.

originally i had to turn the throttle stop screw in more to keep it idling because it would randomly stall at idle.

while driving it it has a horrible lack of power and runs as if its missing a cylinder,

however randomly when just driving it down the road normally(and especially when its warmed up good) it will come out of it and run smooth and like a stock 3.4L should.
but only for a few seconds

then it falls out of this good and normal running "mode" and runs incorrectly again, lost power and like its missing a cylinder. rough hitting idle etc as well as if one of the cylinders is hitting harder than others.



my stepdad said something about maybe they didnt adjust the rockers correctly,. but i dont think so because it iwll randomly run smooth and fine for a few seconds


CEL comes on

ive gone over it completely and everything is connected even the PVC hoses and EGR etc and all looks fine.
i saw the old crank sensor in a napa box in the car so apparently its replaced.


i dont have any real experience with the 3.4 and instead have assembled and replaced and done other work to pretty much any other gm v6 out there, especially the 3800 3300 3100 2.8 and so on

where should i start ?


thanks for any ideas!

 

Did you ever figure this out? I have similar problem. Mike