As the title says. I own Saab 9-3 1.8t 2002 (it's gen II) manual trans, and it has strange and big issue.
Main symptoms: missfires, lots of unburnt fuel from exhaust.
Now about how it gets more complicated - alongside to the main symptoms, there is clicking noise from ECU, when engine is turned off, and hissing sound from around vacuum pump/injectors when it's running and unstable. OBD II tool shows no codes except from missfire, broken lambda probe behind the cat (I'll fix it eventually) and too high voltage. I checked, the voltage is too high by 0.07, so it's marginal. The most important thing - no code hinting what could it be. Next thing - it all is stabilizing at higher rpm's, from around 2500 and higher it's as if nothing was wrong.
Edit: some more symptoms - on low rpm car sometimes chokes and turns off; throttle lag happens sometimes
Also, the fuel level sensor is broken, but this broke long time ago, idk if it's related, honestly doubting it, but who knows.
The stuff I did to the car not that long time ago - new vacuum pump seals, new power steering seals, new battery, new spark plugs, new engine and balance timings, new water pump, regenerated clutch, cleaned MAF sensor, regenerated turbo, cleaned intake manifold, installed ECU protection spacer, new coolant reservoir and I think that's all the stuff that happened under the hood. Timings, clutch, turbo and water pump were done by the shop.
Now, I have a few possible ideas, but I still feel the need to hear what others think.
It could be ECU, but afaik there should be some obd code indicating it most of the time - in my case there is no such thing, that's why I think it might not be ECU. Not for sure, but it is just my intuition.
As for other possible culprits, I figured it could be - vacuum leak, faulty injectors, faulty fuel pump, faulty MAF sensor.
Now, I'm open for your opinions and ideas, help me save my baby 🥺