Just registered on gearhead efi. I am working on a 72 C10 with a 87 TBI 350 in it and am about to pull what little hair I have left out! I am having trouble with the idle surging and missing and thought I would try to datalog using tunerpro to hopefully diagnose something with it. It looks like this is the place to hopefully find some answers.
welcome!
datalogging might help figure out your idle problem
one thing people notice is that tbi systems seem to like very low iac counts at hot idle (the iac being mostly closed), so sometimes just opening the throttle plates a bit extra can help.
...but a mechanical level inspection is also important, verifying integrity of plug wires, lack of vacuum leaks, valves not hung open, spark plugs firing properly... those things may not always show up on a datalog, although you may see a clue or two
Is it ok to just open up the throttle plates a little with the idle screw or what is the proper procedure for doing this? I have put a lot of new into this motor. New AC Delco plugs gapped to .035 with new 8mm Accel wires. Rebuilt Delco distributor with new cap and rotor. New IAC valve, knock sensor, CTS, new heated O2 sensor, new fuel pressure regulator, cleaned throttle body twice, relocated fuel tank to rear of pickup with new in tank fuel pump (getting constant 13.5 PSI), checked MAP voltage and TPS voltage and they are both good and voltage moves like it is supposed to. Checked for vaccum leaks 5 or 6 times and nothing. It idles good until it goes to closed loop after it warms up and then the surge shows up with a miss now and then. Checked for arcs from plug wires in the dark and don't see anything. The only thing that is not making sense is my vacuum reading. I have tried every port on the throttle body and am only getting 17". I bought this pickup with the motor in it and was told it had been rebuilt not too long ago, so I pulled the pan and looked at a couple rod and main bearings and they had very little wear so I went ahead and put it back together. I am just wondering if it has a little hotter cam than stock which is causing my vacuum to have dropped a little and this may be causing the issues? I am not getting any codes at all. I should probably be posting this in a thread somewhere but anyway, this is where I am at.
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