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This is where a scan tool/data logger that can view live data would help greatly. You just monitor and look for the input that drops out. it's not O2 sensors, the ECU has a 12.5% trim limit on those. MAF is easy enough to test, when it's rough just unplug it and see if it helps, though that also is the test for an intake leak. I'm betting there's a bad wire that becomes an open as the wire itself gets hot, I've seen that before. On Levi's car IIRC one of the PTU wires about a foot from the PTU would fail as it warmed up and acted like bad PTU with no spark.
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What kind of diagnostic device would you recommend?
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Those capacitors look original, and they need replacing. Caps go bad over time, and it's the #1 component that goes bad in old electronics. When the capacitors bulge or leak, that's an obvious sign, but they also go bad without bulging and leaking. I just repaired a unit last month that looked perfect, you couldn't see any bad capacitors from viewing from the outside. Anyhow, that person is happy now, it's fixed, and problems are gone.
For diagnostic device, see here:
https://www.3sgto.org/threads/17224-...rs-on-our-cars
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Here's pic of the ECU I repaired with good looking capacitors. Age is the problem, they need replacing.
https://i.imgur.com/wH4XYTi.png
