E36 323i hunting revs and error codes - please help!

Hi all

Please help me cure my car (1996/7 E36 323i) before I drive off a cliff or buy a Polo (no offence meant, I would seriously consider a TDI).

Symptoms:

• Sometimes would not start. Metallic like sound when starting. If I depress the accelerator pedal for +- 5 seconds, turn the ignition to on, wait a second or two and then start it always/almost always starts. I replaced the crankshaft position sensor with a Goldwagen (Febi) one and a couple of days later the metallic like sound started to happen.
• When driving through water, the car would start to miss/die when pulling away from a stop and struggle to start afterwards. I've sprayed water with a hose under the manifold at the region of the crankshaft sensor and after a while the engine died and wouldn't start or start but would sound like it's not running on all 6 cylinders and die. Don't worry, the engine was cold.
• Hunting revs, sometimes just a little and other times quite violently with fluctuations of 500 RPM or more. This does not happen as a rule but would happen any time; just after the car was started or start doing it when driving for a while. I can control it by keeping it at about 800-900 RPM. It happens regardless if the engine is hot or cold.
• Sometimes the car would bog and/or surge. When coasting I can see the econometer fluctuating.
• Heavy fuel consumption; +- 7-7.5 km/l in town.
• Sometimes a sulphur like exhaust gas smell is present.
• Sometimes the car would not feel as brisk as usually when accelerating.
  

What I've already done:

• Replaced CCV
• Cleaned ICV
• Replaced all vacuum hoses except the U shaped one at the ICV. I was leaving on holiday and couldn't get that one on time
• Cleaned MAF
• Cleaned throttle body
• Replaced spark plugs
• Replaced fuel filter
• Had fuel pressure tested
• Had O2 sensors cleaned at Diesellec/Diesel Electric using an ultra sonic machine used to clean injectors
• Replaced throttle valve potentiometer with a Goldwagen (probably Febi) one
• Replaced crankshaft position sensor with Goldwagen (Febi) one
• Tested a couple of times for vacuum leaks by spraying everywhere (all hoses where I could reach, manifold, air intake boot) with Q20, carb cleaner and water
• Replaced leaking valve cover gasket
• Replaced VANOS seals
  

The O2 sensors were cleaned after getting error codes for them.
The throttle valve potentiometer and crankshaft sensor was replaced after getting error codes for them.

Most recent error codes:

• 12 Throttle valve potentiometer
• 83 Engine speed/crankshaft position sensor
• 200 Oxygen sensor voltage rise 1
• 100 selftest ECU
  

All of them except the last one have occurred previously. The oxygen sensor error only re-appeared more than a year after they had been cleaned.

My thoughts:

• The aftermarket throttle valve potentiometer and/or crankshaft sensor are crap? Replace with very expensive OEM parts?
• Problem with crankshaft sensor connector at the engine, causing intermittent problems or stalling when it gets wet? Alternatively, the aftermarket sensor's connector is the problem?
• Replace O2 sensors? Are Bosch sensors OK?
• ICV seems fine after cleaning it. The spindle valve can move freely where it was a bit tight before. Any way to test this?
• Should I be concerned about the ECU self test code?
  

I used INPA to read the codes (OBD setting on my cable, MS41.0 for M52 option in software).

I would really appreciate your help. I've already spent a lot on this car and don't want to incur any unnecessary cost by simply replacing parts by trial and error.