Hey all, my brother has a '94 K1500 that he want's me to look at for him, and maybe someone can point me in the right direction to start. He had it at the Chevy dealer and they were unable to fix it.

The engine has a surging idle and decreased power.

The engine will start and idle fine for a minute or so, then start surging like it want's to die. He can pull up on the EGR diaphram and then it will idle smooth, and return to a poor idle once he let's go.

Here is a copy/paste of what he says he has replaced:



Here is a video of the idle. It sounds worse in person than it does in the video. When he pulls the EGR away from the intake it will idle smooth.

 

Some EGR valves are designed to move by either vacuum or pressure. If the engine idles smoothly when the EGR diaphragm moves in a direction away from the engine, then it might be that his new/replacement EGR valve is the wrong one. IIRC they have stamped labels on the frame that are either P or N (positive or negative) for the type of pressure needed to make it operate.

IOW EGR is supposed to be close, non-functioning, at idle..... and yet your brother's engine runs better when the EGR is open. That suggests the EGR valve fits but is opposite in function. Maybe the EGR valve was in the wrong box when he bought it.

edit: it's also possible that he has the vacuum lines to the EGR solenoid and/or valve improperly attached to the wrong location.

See also: https://www.thirdgen.org/forums/tech...e-testing.html