91 Z28 5.0 5speed
Recently had tune-up plugs,plug wires,distributor cap, rotor,new injectors,fuel pump,fuel filter.

when your at idle the car shakes when you shift to change gears it will back fire and shake in low rpms. all the plug wires are in correct order and the timming is also correct.I pulled the plugs cylinders 5,6,7,8 look to have oil on them. cylinder 8 look to have a flat black look,cylinder 5,6,7 had a bit of a gloss look to them.Is this valves? worn rings? the car is not burning any oil.

 

Check you fuel pressure.

 

Checked fuel pressure

With key on
40 PSI, in about a minute in drops to 30psi

With the car running 35 psi with FPR vac line off 43 PSI

Possible fuel problem?

 

A leaky diaphragm would make the gauge needle wiggling or would not keep the pressure at all.

Just to make sure, you put same size injectors? Do you have any check engine code?

 

Injectors are 19lb and no check engine light.

 

Bump

The car smooths out past 2k rpm any thing under that and it is shaking.