Like nathan97zook, I have a 97 SV420 180000kms and have the exact same symptoms. 1200 to 4000rpms the engine will sometimes stall randomly. It has only started this since 4 days ago. Some trips it'll be fine and others itll try and stall/surge at any speed, - revs will instantly drop to 0 and the engine feels rough and sputters back to where the revs were, but sometimes itll drop to 0, sputter and completely stall, even at highway speeds (VERY SCARY). Other times, just idling or waiting at a traffic light, it will stall and ill have to turn the engine back on (normally 2-4 times if this happens). Before these symptoms happened, the engine light would sometimes come on at 110kmh and above and goes away after driving 60kmh for a while (this still happens). After reading Stueys post it sounds like this is caused by faulty coilpacks not burning the fuel properly. I have shorted the diagnoses wires and code 13 pops up, I have ordered an o2 sensor in hopes this will solve something but am not confident after reading other posts.
So, could the unburnt fuel be clogging up the cat causing back pressure which would cause the weird stalling issues? Is it the idle control valve, although idle is not rough, its consistent but the engine only sometimes will stall. I have started it with it unplugged and revs are the same at idle and feels exactly the same as when it is plugged. Would the air temperature in the air box being faulty cause my symptoms. Wondering if anyone else has had similar issues and has a pretty sure idea of what it could be.
I am yet to get a multimeter to check if wires are faulty but its next on the list to diagnose but thought id ask to get a narrower idea of what it might be.
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