So I screwed in the idle screw till it would stay idling at about 950 rpm, and ran it long enough to go closed loop. Once it goes closed loop the fuel trims start to go negative and the o2 sensors switch back and forth from rich to lean. Closed loop

 

Ideally, you want it to idle around 650 or so. Still looks like your idle is unstable though? Fuel trims look good. That's what I expect to see. Long term will take a while to show anything.

 

Hows your battery? I have no clue if its related but my old 96 I had in high school, i fought the iac on that something terrible. First time had a shop work on it, they replaced the IAC, after that bill I started doing more work myself. Seemed like once a yea ri had to take it out clean it or I would get the no idle/stall issue, one time cleaning didnt fix it, fouight and fought it, was after i bought my second truck and it was sitting more the battery was weak, always had to jump it, wouldn't stay running, replaced the battery, suddenly the idle issue fixed itself

Just because I've had this happen on multiple different vehicles/engine. Have you tried testing for A/C voltage at the batteries, I have had these failed diodes cause mystery problems on at least 5 different vehicles of all brands/engines

 

I had just screwed in the idle screw to bring the rpm up enough for it to stay running long enough to go closed loop to make sure the O2 sensors were doing their job once warmed up. I'm not intending to run it that way long term. With the idle screwed in like that its running with the IAC completely closed. And it still died about half the time when I pull it into drive or reverse.

 

Battery is a 1yo Napa marine deepcycle/starting battery that has had a trickle charger on it off and on over the last few weeks while ive chased this issue. I tried swapping it out with a fully charged yellow top optima earlier in the troubleshooting for this and it didn't make a difference. I also made sure I had good grounds when doing the swap. I have 2/0 braided copper cable from negative directly to engine block, starter bolt, frame, body tub, and the winch negative lug. I have not checked for AC voltage at the battery or checked alternator diodes. Thats a good idea, I'll check it in the morning. Thanks man!

 

Took a couple data logs looking at timing because a guy at work said thats about the only thing I haven't messed with yet. It seems like it advances the timing right when it starts its rpm drop and it never comes back from that.Data log

 

Timing isn't adjustable. It is purely controlled by the PCM. Turning the distributor changes injector timing, does nothing for ignition timing.

 

I understand that, I'm just looking for anything that could be causing my idle to surge and then the engine to die. I've gone through everything I can think of and nothing has helped.

 

Idling high, but IAC is zero? What??? That's not right.

Reset the PCM...... Disconnect the battery, turn the headlights on, count to 10. Headlights off, reconnect battery, turn ignition to On, do not touch anything, count to ten. Start the engine. It *should* figure out idle pretty quick. Why yours isn't, is a mystery.

 

Tried that reset, didn't make any difference. I've also tried resetting the fuel trims and reset all adaptives. Nothing has made a difference.