i have a 1999 Z28 LS1 it misses a little bit at idle but it misses really bad when you accelerate. I have changed pluges, Wires, cleaned MAF, new injectors, 2 new o2 sensors, new fuel pump. Still misses
MODS:Slp air lid, K&N, Headers, no cats
TROUBLE CODE: P0174

If you have any ideas please let me know Thans

 

Have you checked for vacuum leaks?

PCV or Intake manifold leaks?

 

Do you have access to a scanner with "GM Enhanced Parameters"? It can recall the misfire count by individual cylinder, which may point you to the problem.

 

I would look for leaks and such on the passenger side of the intake (indicated by your code). Could be an intake gasket. The PCV come in on the passenger side up by the throttle body too, and those lines are known to crack. That misfire by cylinder could be key too.

-Geoff

 

def sounds like a intake leak... did you check that none of the new plugs had any cracks in the porcelin? I've seen how plugs nib can be thrown around during store transfers... also.. check for cracks in your coils too.