have you tried another ECU yet?
check your fuses, seriously, sounds like when my 16v that i drove for a year didn't have a good fuse for the isv and all the fine tweaking modules
'87 GTI 1.8t, '03 20th GTI #2100, '96 Ranger 4x2
'01 TT 180Q, '98 Ranger 4x4, '01 Catera, '90 GLI 16vT, '94 850 Turbo, '90 Golf, '89 Golf, '90 Mustang LX, '91 Jetta, '88 9000S, '86 Jetta, '91 Continental
Have you checked and/or replaced all your ground wires? I know it seems minor, but I had an idling issue that drove me nuts for a month, and I fixed/ replaced a lot of what you did, then asked for help on the 'tex-- in the end it was a bad ground wire to the head.
^ Shotgun much?
OP, second on the grounds and ecu. Having done everything else that you listed, the management was the next thing I thought of. I tend to not suspect the ecu and lean more toward brittle/broken wiring, but give it all the diagnostics to isolate the cause. Don't send that to a yard if you decide to let it go, sell it to someone else or part it. Hate to see a good one waste away in the boneyard.
this is exactly what i'm not a fan of cis-motronic (though my audi 5k runs perfectly *knock on wood*)
here are a few of my ideas (some may be far fetched)
- vacuum leak (like everyone else said)
- dead spot in your air box's potentiometer
- tweaked hall sender window in dizzy
- bad signal to ecu, bad signal to coil stage
since you mentioned bumping the harness and a few seconds of decent idle... i'd not only trace the harness for continuity, but also measure resistance. most likely there's an issue with the wires between the fuel distributor and the ecu.
it's a huge pain in the ass, because it's tedious work, but the one thing i've learned is to never trust a harness (even if you've built it yourself).
years and years ago i had an 88 digi car (split year) that didn't match ANY wiring diagrams anywhere, and had some mysterious gremlin that i just couldn't track down for months. i replaced this and that and nothing made any difference.
finally, while at my wit's end, i took a day and rebuilt the entire engine harness, reusing connectors, but rerunning and repining everything, and the gremlins were gone.
EDIT: you can also bring it up to me in brooklyn for a few days and i'll get it sorted for you.
I would suggest pulling the entire harness from your bay and go wire by wire. Replace and re-pin as needed.
~25 year old copper wiring loses a lot of conductivity due to oxidation. It MAY have started out as oxygen-free copper (kind of doubt it..) but I highly doubt it is now.
VR swap. /thread
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I took the harness out. Cut most of the covering off around where I tapped it and it ran better. Didn't really see any issues with the wiring. The coil power stage harness was fixed when I installed that harness many years ago. Still all holding together. The DPR wires however are split at the connector. It is still connected and resistance isn't too bad. I have a feeling that this will be the end of it. Unless somebody has a good fuel distributor laying around that they want to sell cheap?