1992 Blazer Rough idle in gear only
 

Mine is a 1992 full size blazer with the 5.7L w/ 225K, it idles rough only when in gear at a stop. It runs just fine 95% of the time when in Neutral or Park, this only started a few months ago and I am at a loss. When it does start to stall the oil pressure drops as well. At this point I just roll up to stop signs/lights in neutral. I am trying to sell this Blazer so any help would be awesome to get this thing running right again
What I have tried:
-plugs and wires
-new injectors
-cleaned the EGR valve but not replaced
-new O2 sensor

Someone recommended a fuel pump but that doesn't make sense since it runs just fine when not in gear. However, after I replaced the injectors it ran good for like 6 blocks on my test drive and started doing it again... Maybe fuel filter???

PLEASE HELP LOL

This is a shot in the dark, but could you have a vacuum leak? If it came on all at once, perhaps a vacuum hose fell off, was not replaced, or developed a leak?

I'd also suggest cleaning the throttle body and the IACS valve. I had a similar symptoms with my '02 Sonoma that turned out to be a crusty IACS valve that would stick and not allow sufficient air at idle. Cleaning it and the throttle body thoroughly with SeaFoam intake cleaner and a toothbrush solved the issue for me.

Bye engine. Its about to hand grenade. Oil pressure is the key.

Bad rod or main bearings. Maybe a bad pump.

Even cranking on the starter which should be around 400 RPM should generate most of full oil pressure.

It's losing oil flow and the pistons or crank are dragging. Saw thus happen in my old dodge van. The rod bearings were gone bc the previous owner used 20W50 in it year around.

Check the internals by trying to rotate the engine by hand. Might feel rough spots.