Engine lopes while idling

run fault codes
check for dirty injectors

Lets start at the beginning. Did anyone check fuel pressure before and after replacing the pump ?
Has anyone checked the fuel pressure regulator and the injector spider ? The 4.3w engine uses a spider with one injector that supplies all 6 cylinders. And it runs at 65psi or more.

Try cleaning the mass air flow meter. There;s a spray cleaner you can get at an auto parts store

engine check light should be on
check theses things
engine timing
idle control valve
TPS
crank angle sensor

Check the fuel pressure it souds like you might have a weak fuel pump.The fuel pressure should be 60-66 with key on engine off.

1. Vacuum leakage Check throttle body and intake manifold for tightness. check all vacuum hoses.
2. Faulty fuel or pump or electrical.
3. Plugged PVC valve.
4. Air filter clogged
5. Leaking head gasket.
6. Camshaft lobs worn.
All of these porblems can cause lopes or erratic idle.

You could have a clogged fuel filter, if you haven't changed it in awhile. You could have a leak in the intake system somwhere also. When you slow down, you get less power to the engine. It may need spark plugs and wires as well, if in need for a tune up.

replace the electric part of the ignition down on the steering colum ....u will have to drop the steering colum down but not totaly remove...fixed 2 s-10 trucks same year that way

ENGINE LOPING CAUSED BY.LEAKING BY VACUUM LEAKS AT THE INTAKE MANIFOLD.CHECK ALL BOLTS ON THE INTAKE MANIFOLD TO MAKE SURE THEY TIGHT.YOU COULD HAVE LEAKING EGR VALVE OR PLUGGED PVC VALVE.DO A COMPRESSION TEST TO CHECK FOR LEAKING HEAD GASKET.DO A FUEL PUMP TEST CHECK FUEL PRESSURE.IT SHOULD BE 35 - 45 PSI.IF FUEL FILTER HAS NOT BEEN REPLACED.REPLACE IT FIRST IF FUEL PRESSURE TO LOW.DIRTY FUEL INJECTORS WILL CAUSE LOPING.TIMING CHAIN WORN.IGNITION TIMING OFF AND WORN LEAKING VALVES.AND WORN CAMSHAFT LOBES.ALL ABOVE WILL CAUSE ENGINE LOPING OR SHAKING.

This usually happens when the fuel pump is loosing pressure.

I will just advice you make a replacement on the fuel pump. It is located in the fuel tank beneath the back seat.

Be sure to consider the rating on the fuel pump when replacing.

Good luck and rate my solution.