ok, 1992 chevy silverado 4x4 w/ 5.7liter. All stock. I towed my 18 ft fifth wheel trailer appx. 50 miles and afterwards my engine will idle fine and drive fine but when you simply try to mildly idle along in gear w/ out giving it any throttle (such as rolling away from a stoplight after it turns green) it will spitter and sputter. Some times it seems like it might die but if you give it throttle it runs fine. Highway speeds are fine. I changed the fuel filter. It seems intermittent as some incidents are very bad and others it won't do it at all.

Has recently had new cap, rotor, and plugs.

What's going on here??

 

check fuel pressure with a gauge. clean the idle air control valve and egr valve. also, is check engine light on? if so, get the codes, we can help better with them.

 

Yes, I did a code test and no codes popped. Just 1-2 for diagnosis working. Was thinking perhaps weak fuel pump also. Will check idle air control valve and egr valve. Seems funny that I had no issues till I towed the trailer....seems something gave out due to the increased forces from the towing load....

What should I expect for optimum fuel pressure? And where should I check it at? the engine or outta the tank??

 

up by the motor on the fuel line before the throttle body, there is a test port. this is where you test the pressure. with rig running, pressure should be 11-13psi, if memory serves.