Hey guys I'm hunting a ghost. I recently moved to Georgia and they require emission checks. So I've started replacing items that did need to be replaced. TBI base gasket, PCV, some vac lines, cap rotor plugs and wires, and a new EGR valve. Now the funny thing was I was chasing a slight mis fire at idle (Which is still there). The car ran great before I started all this and with each repair it seems to run worse! The latest being the EGR valve, I have a wonderful little stumble right off idle now and it's madening . Could a possible exhaust manifold leak cause this lean mis fire or should I be looking at something else. Thanks

 

How do you know it's a lean misfire? What are your O2 readings? What are the fuel trim numbers?

Idle air bypass clean? Idle air control working? Correct PCV valve installed? Computer getting correct engine coolant temperature reading from sensor?

Exhaust manifold leak would more likely cause a rich mixture. Air entry to the exhaust stream would show false excess O2 in the exhaust--lean mixture = rich command.

 

weak fuel pressure can cause the off idle stumble-my
crossfire did that when the fuel pump was going bad,
pump replacement/upgrade completely cured the
stumble.