What's up guys, I'm new to the forum, and e30's, but not cars in general. My 85 eta has developed a fun issue that has me kind of stumped, I've seen a few other threads with similar issues, but no resolution, so I'm hoping we can finally get to the bottom of this.So here's the story: I bought a lemon, 1985 325e (m20b27), minty interior (I thought) and pretty straight body. Ran beautifully (minus a high idle, IACV) and drove well. Once I got it home I realized that I had been screwed over, PO had covered several rust holes in the floor with sound deadening and undercoated them, the only way I found out was that I noticed some rust by the throttle pedal pivot and pulled the carpet back to find a nice hole right next to it.
Fast forward about a month, and I've patched all the holes (battery was disconnected most of this time as a safety measure while welding), replaced the booster and master, and a few fuses, changed oil, flushed coolant, and adjusted valves. Intake plenum had to come off to get the booster off, so new gaskets there. I go to start the car, and it runs like garbage (bitch pipe leaking too, but that's unrelated to running issue) no spark on cylinder 4, replace plug wires, coil, and plugs (friend used to have an m20 car, gave me coil and wires, plugs were black and old) Idles great, IAC actually works now (fuse, I assume) and I think I'm good to go.
Now for the fun part: when the car starts to warm up, it still idles ok (sometimes it'll drop and miss a little, but it's an old neglected eta) and free revs fine IF you tip in gently, any quick throttle application makes the engine miss and shudder, revs basically stop climbing, this continues until you back out of throttle (to probably 10%). same story while driving, ease in and it runs beautifully, can go full throttle, and all the way to redline (whopping 5k that it is) no problem as long as you are smooth and slow with the application, any quick press of the throttle and it shudders and falls on its face. Shudder feels very spark related, or at least rhythmic, and regular (think rev limiter). definitely get's worse the warmer the car gets (more sensitive to application of throttle, shudder does not change character based on temp).
TL:DR: I let My Eta sit for about a month to fix rust, now she doesn't like the heat. Slow throttle application is fine, quick throttle and she falls on her face until you back out, threshold for "slow throttle application" get's slower the warmer she is.
What I've done:
Plugs: Replaced with new autolite coppers (old were different brands and gross)
Wires: Replaced with used, known good set
Cap: visual check, looked very clean, sanded contacts lightly to remove corrosion
Coil: one in the car was a generic and wrong size, replaced with used known good bosch unit
Valves: adjusted to within spec, this was maintenance before the issue presented itself
Booster: before issue presented, was leaking, had to remove plenum for this
Plenum gaskets: new, see above
Vacuum leak check: pressurized intake, found and fixed a couple, no change
Temp sensors: checked resistances on all 4, all were proper
TPS: checked resistances open and closed, seems to function properly, issue presents whether plugged in or not, but unplugging affects idle/off idle response
O2 sensor: unplugged, no change, heard these don't do much, especially on earlier cars
AFM: checked voltage (resistance first, but then realized that's the wrong way) climbs smoothly through the full sweep, temp sensors have normal resistance
Baro? sensor: on the airbox, resistances checked out based on the internetz
ECU: visual inspection, no obvious cold solders or anything, didn't fully disassemble to look at components
I'm really not sure what's going on here, I'm not a fan of the "replace parts til it's fixed" approach, so I'd really prefer some input, the fact that it's transient and related to how fast throttle is applied, not actual position, makes me thing AFM, TPS or ECU, but I'm not familiar with these cars, and it seems the design ideology is fairly different from my typical Jap-crap, so maybe I'm missing something simple.
TIA,
-Nathan
Edit: Found it, PO had soldered a resistor inline with the coolant temp sensor (to fool the ecu into running richer/different timing I guess, car is one big hack job really) Wire broke, so I fixed. Runs beautifully, glad I bought her for the first time since the drive home.
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