So, somewhat weird, intermittent issues with my dad's 1989 Cutlass Ciera, 3300 engine, 4 speed auto.
Sometimes, maybe more than not, immediately upon startup, it will high idle for a few seconds as intended, then nosedive down below 500rpm far half a second, then shoot past 1000, then stabilise at normal idle rpm. When you immediately put it in gear (especially reverse) it will almost stall (sometimes does) and then accelerate as the rpm jumps up before stabilizing. Warm idle is 675 (factory spec).
2nd problem is that sometimes, rather rarely, but it's had it before in the past, it will occasionally have massive misfires in 3rd/4th with the TCC locked. Cruising there's nothing, but any acceleration before it kicks the TCC off, it will misfire really badly, just completely lose all power for a fraction of a second, then get it back, then lose it again, etc. the result shakes the whole car like the engine's trying to escape! In the past this problem was apparently solved with fuel injector cleaner, but that doesn't make sense, as it doesn't matter where the gas pedal is and where the rpms are, only happens when the TCC is engaged, and even when it is happening, it seems to go away once the engine reaches operating temperature.
Solved the first issue, and that may have had to do with the second too, there was an elbow connector plugged into the bottom edge of the intake, which had come fully out, I think PCV valve, anyhow, big vacuum leak, the startup enrichment led to a stable start, then once that finished it went lean, stalling or very close to it, until the o2 sensor was able to stabilize the overall mixture (still lean on some cylinders, rich in others, causing excess vibration). Plugged that back in, starts perfectly, throttle response is improved, spins the tires of the line at half throttle (never did that at all before), brakes will lock up all wheels (never did that before, my thought is less vacuum pressure) and my dad thinks it shifts better to (more low end torque maybe?).
