I have a '94 Chevy Blazer Vin W. I have totally rebuilt and replaced almost all sensors and components. These are heater core, distributor, cap, rotor, wires, plugs, ecm, map sensor, tps, egr valve, coolant temp sensor, oxygen sensor, fuel pump, fuel injector, fuel line kit, ac compressor, ac drier, lf window motor, water pump, fan clutch, reman cylinder heads, ignition coil, front and rear brakes and wheel cylinders, new shocks, iac motor, starter, battery, and knock sensor. Some days the vehicle runs fine. Other days it searches for idle and runs rough under load. It kind of makes a popping noise. I have a lot of money invested in this vehicle and I'm hoping someone can help. We first thought it was a fuel problem with the way the truck was acting, but replaced all fuel compents with and put on a new fuel injector. The only thing that I think it could possibly be is the pcm. That's the only component we haven't replaced. Any ideas would greatly be appreciated.

 

You didn't mention the cat. If that is plugged, it can cause a lot of problems.

 

The rough idle and roughness underload are both intermittent. The cat seems to have good flow. Took it off and cleaned it. Maybe it needs replaced. I actually found out that the pcm has been changed. Don't know if I got a faulty one of those or not though. Any other ideas of what to test??

 

Its probally the fuel injector connector, that plug that connects onto the top of the Spider inside the plenum. The rubber spacer goes to mush from being exposed to fuel and cause's a loose connection. Theres 2 wires, red and blue that run out the front of the plenum on the driver side. Wiggly them while its idling and see if it acts up. I figure its this, becuase you say underload, so the connector vibrates and causes a poor conection. Its a $10 fix at Autozone.

 

After more careful inspection, I got the bright idea of unplugging the egr to see what would happen. Idle smoothed out and could rev engine with no hesitation. There is a three way check valve on the back of the intake. When I inspected it, I noticed a small crack that was allowing the intake to get too much air. It was intermittent b/c when it was turned one way the crack closed and the other opened the crack. Replaced the three way valve and the truck is running like new. Thank you to the people who helped me narrow it down. I just wanted to post the fix in case anyone else runs into the same problem.:icon_raz z:

 

x2 - That part is my friggin nightmare. My fix was to solder on a new connector, then before putting it on the injector I put 2 of the tiniest Orings on the pins, then press the connector on and its tight as all hell now. Its a whole $8.00 and the dude will give you 4 of the tiniest rubber rings hes got. You need the ones that stretch a little over the pins on the injector.