Misses, runs rough when damp or raining 1996 Corolla 1.8 Auto. 224K Miles

#1
Okay, So my main complaint is that the car runs like heck when it's damp or raining, and also shifts like crud I'm guessing because the engine is not firing properly. (been doing this for about 8 months). Here is the pertinent info:
  • Engine Code P0401 (Low EGR Vacuum) That has been on for years, but ??? hasn't caused ??? the recent problem. When cleared comes back on within a couple of days.
  • Engine Code ????? (cylinders misfiring) gets thrown when running rough, again only when damp or raining. Has to be cleared with the reader.
  • Recently replaced: Plugs (gapped properly) (dilectric on all of the electrical/s replaced), Plug Wires, Full Distributor including Dist. Cap and Rotor, Vacuum Switching Valve, Egr Valve is about 1 year old and works (with vacuum testing), EGR solenoid, Engine Thermostat is about 1 year old, Throttle position sensor is about 1 year old, Front O2 Sensor replaced about 2 years ago.
  • Had shop clean the Throttle body and the Upper Intake manifold. Passages not completely blocked they were at about 50% plugged.
  • All fluids are kosher, All parts are OEM (denso or toyota) bought from an auto parts store not Ebay. Timing Belt is about 20K miles old.
Any help would be greatly appreciated, Sorry for the long post but my philosophy is more information will hopefully result in better / easier diagnosis. I've included everything I think is important.

Thanks,
Ken
 
#3
If it only does this when damp or raining I'd check for any leaks, all possible ways that water may be entering the engine this can/will cause a misfire. Also 96 is OBD ll so I would check to see which cylinders are misfiring
 
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