Okay so the blazer (4.3 cpi) runs rough for the first few mins on start up when cold. Ive ran seafoam through the brake booster vac line then let it sit for 15 mins then drove it till it stopped smoking. I cleaned the EGR valve and made sure it wasnt stuck close. I changed the O2 sensor and scrubbed the throtle body. Its got a new cap, rotor, and bosch plugs. I did a fuel pressure test and it was at 55 psi while running and 53 ten mins after it was shut off. I plan to change out the plug wires soon but Im running out of stuff to check to find whats causing the problem. Possible the module or coil?

 

Sounds like an open loop problem, when you say running rough can you describe the condition more? One thing you might try is resetting the computer by disconnecting the battery or pulling the computer fuse, several minutes should reset it. I doubt it's the ICM since the module only controls the spark during start up, after that the computer takes control of the spark.
Here's a link to the control module:
http://easyautodiagnostics.com/gm_ic...n_module_1.php

The coil causing the problem would mean it's temp related, that's the only thing I can think of that would represent a time issue. Seems to me if the coil was the problem it would be causing problems cold or hot, but you can always do an ohm test on the coil to check it.

 

Thank you for replying. On start up when cold it shakes badly and the engine light comes on but after a min is clears out and runs smooth. I will try new plug wires and resetting the computer.

 

I'm wondering if there may be a problem with the EGR valve to where it isn't sealing up. This would have more of an effect on a cold engine than it would on a warmed up engine.

Another possibility is a problem with the ECT (engine coolant temperature) sensor located in the lower intake manifold near the t-stat. If for some reason this sensor isn't registering cool temperatures (stuck hot), the engine wouldn't be in fuel enrichment mode when cold.

 

^^^ I unplug mine when the motor is cold just to see what happens and the idle changes. Try starting it cold and unplug it and see if idle changes.

 

lots of good advice and compiling a new list of things to check. I thought about the ect sensor at work today.