73-87 Chevy _ GMC Trucks > Engine/Drivetrain

Cold Engine Problem

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boll213:
I just finished a 350 for my 87 4X4.  It is a driver with a few exceptions - balanced, forged pistons, everything new, small cam (Comp Cams says it works fine with ECM/TBI), fresh rebuild of TBI (I've tried a Holley replacement also - no real change).  The problem I'm having is that when it is cold, it runs rough - doesn't really have much power - I have to pump the accelerator (like a carb) to get me down the road.  After it warms up and I've shut it off and restarted - it runs fine - no problems at all.  I've changed the O2 sensor and the TPS - no improvements.  I thought about switching to a heated O2 to see if that would help, but haven't had a chance yet.  Any chance at all this could be a bad cap or wires (these are all also new - Accel, but could still be a problem)?  I've heard, what seems to be spark jumping (not much - maybe once every minute or so - doesn't really seem to effect the engine idle though) - but can't find it anywhere - tried looking at night and can't find any spark crossing over or jumping.

I'm stumped - any help at all would be appreciated.

Thanks.

aprice:
did you replace the vaccum lines? heres my thoughts, there could be a vaccum leak, and until the rubber lines heat up and expaned they are leaking, to cause it to run rough. I hope that makes sense to you, lol its been along day

roundedline:
I am just thinking aloud, (hard to diagnose without actually witnessing the problem)  Have you changed the fuel filter?  Is the IAC acting up? Did you check the previously mentioned vacuum leaks? Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

boll213:
I believe I've found the problem - bad EGR vacuum solenoid and a VERY slow vacuum leak in the EGR valve itself.  I'm replacing them both for good measure.

Sort of on topic / off-topic question.  The TPS that I replaced isn't adjustable.  Should it be.  I checked the voltage and it seems a bit high - about .70 volts at idle - but there isn't any adjustment in the switch.  What if any problems could this cause???  Will it make it run rich?  Less fuel economy?

bowtieguy:
what about your fuel filter?????  Is it new as well?  Stumped me on my 94 TBI for a while.  Also check I believe numbers 5 and 7 plug wires, if they run beside each other they can jump spark, but that would happen at all temps not just cold.  Good luck.

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