Engine 90 LX 5.0 won't keep running, dies at idle

Jaybal80

Member
Sep 16, 2019
2
1
13
40
Wintersville OH
How I got here: I got this project mustang 2 years ago and it was in all kinds of disrepair. The transmission as pulled and never put back, the engine was supposedly 'rebuilt', but never run (the block was in the engine bay but no accessories bolted back up.etc..- I've spent a ton of time un-doing the stuff a prior owner did wrong). Long story short, I had a new (to me) AOD with 76k put in with a new TC and got the engine accessories put back in. Initially I had a no-start issue, so I went through the checklists and found some ignition and fuel issues that needed resolved. Ended up finding a slew of bad or questionable components that I replaced (got new plugs, wires, coil, IAC, TPS, Dizzy, TPS, fuel pump & filter, relays, etc, rebuilt the injectors, etc...). Finally was able to verify spark, compression, and fuel. So now it starts, which is leading me to my next problem...
I can start the car, and it'll rev up in a cold start to 1100ish RPMs for a few seconds and everything sounds good. Then it'll settle down to idle and starts loping around 550-600. It'll struggle for a minute or so before dying. If I give it some gas it'll rev up, but as soon as I let off it starts struggling again. Fuel pressure is good, although when I bleed the tested it does have some air bubbles in the line - I haven't replaced fuel lines yet. Plugs are properly gapped and I'm getting spark in each cyl.

I have a code reader but my test port is wonky and I have to hold it a certain way to keep en established connection with the PCU. My KOEO codes are 81, 82. 84, and 85. This car at some point had the smog pump/cats/related accessories and AC pulled. From what I can tell, it was done mostly right - and I went over the vacuum/SMOG diagrams and made sure what needed to be capped was and that there were no issues there. I THINK these codes are all smog hardware related - can anyone confirm?

I got my code reader plugged in and started cycling through KOER and it actually went from it's death lope to a steady idle while the test was running - I don't know if that was coincidence or if something the PCU did in testing did it (and if so what was it) but then my wonky test port lost connection and resumed it's rough idle before it gave me any codes. I'll try pulling KOER codes again tonight, but if anyone has any ideas as to what could be causing this I'd love to hear it - I'm at a bit of a loss. Thanks in advance!
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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polk county florida
Go through this checklist step by step, don't skip around.
Clean and check the connections for the diagnostic port so you can get good readings or use the 'hairpin' method
 

Jaybal80

Member
Sep 16, 2019
2
1
13
40
Wintersville OH
Go through this checklist step by step, don't skip around.
Clean and check the connections for the diagnostic port so you can get good readings or use the 'hairpin' method

Thank you, I hadn't seen this checklist before so I'll start going through it tonight - the no start checklist was a HUGE help in getting it this far!. I think I need to try the hairpin method - I've tried cleaning the port already to little avail.
 
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