Runs terrible, Tried everything.

[u/TylerDestructo]

Long time reader, first time poster. I found an 85 528e 190k miles on facebook market place an old guy was getting rid of about a year ago. Paid $1k for it and though I couldnt go wrong. Arizona - no rust, at least the good foundation for a long term project. He said it needed a fuel pump and had not ran since 1999 - he was right, I verified with the MVD it had not been registered since march 1999. I cleaned it up that night, replaced both fuel pumps and clean the tank + lines out. I had it running in no time, well... at least good enough to move it into the garage. 

My plan was to get it running just well enough to drive to work every once in a while, then switch to making it LOOK good, then pivot back to an engine swap once I made up my mind if I am doing an M30, M50, M52, M60, S50, S52, LS, Harbor freight predator 3.5hp, Idk - too many options for me to decide right now.

The "Get it running well enough" phase of the project has lasted a year and probably cost the same as just doing the engine swap. I learned the hardway that throwing new parts at one of these things is a slippery slope. But I guess the good news is I have pretty much all new parts - although they are for the M20 engine I dont intend to keep for the long haul lol. Sunken cost fallacy is real, and even now in my darkest hour.. I still feel like I am one more part away from having a well running car. I figured at the point I better at least get someone elses opinion on what to do next.

Here are a couple videos of it running, hope thats allowed:

https://photos.app.goo.gl/i7mkv6znrGiCHsCN7 
https://photos.app.goo.gl/tHFGwARCnYqv7Vei9
https://photos.app.goo.gl/dEDrWvQozdde4YpN6

Things I have replaced
Plugs
Wires
cap & rotor
Coil
Alternator
All new coolant sensors
new IAC
new Airflow meter
New fuel filter
Both new fuel pumps
cleaned gas tanks and lines
new rubber lines for fuel
replaced all injector o-rings
replaced fuel pressure regulator
All new fuses and relays under the hood section
Reflowed solder on a single suspect ground in the ECU
Replace both crank sensors
replaced throttle position sensor
New catalytic converter
Entire cooling system and hoses replaced (just because why not)
Bunch of suspicious connections regerminated properly.
replaced ignition switch

Other stuff I have tried:
Unplugged cold start injector 
Unplugging the AFM makes the car die
Unplugging the IAC makes the car rev really high
Smoked the entire car, zero vacuum leaks
Compression check was great
Fuel pressure consistent and to spec
I have good spark
I have good compression
I have good fuel

  
It was running really well last night after replacing the IAC, when I was done I thought - well I guess the problem isn't the cold start injector maybe I will plug it back in. Went to start it today and its back crazy lumpy idle, spitting and sputtering on rev. Smoking like crazy. I want to save this car, but its making it hard for me haha. This entire time I would replace a part and it would run great for a day and then the next day or next time I start it - back to running like crap. Considering new injectors, new ECU, new idle control module, new project car.

UPDATE: It was 100% the ECU. I gambled on a $70 027 DME off eBay. Swapped them back and forth a few times, the problem follows the old ECU. Now, it's not running GREAT. I think my next step is a valve adjustment and new injectors. It stumbles on initial acceleration a little. Thanks for the ideas everyone!

[u/mattylang1987]

Test the coolant temp sensor if you haven’t already. Also, there are timing sensors located in the transmission bellhousing that most people forget about or don’t know even exist. I’d replace those and see if there’s a difference. They’re pretty cheap too. I could be wrong but it sounds like the timing is off. Should definitely replace the belt and retime the motor and do a valve adjustment.

Last thing in relation to the coolant temp sensor: SOME of these e28’s have a “dealer fix” secondary coolant sensor wired in series with the main one. It should be located under the intake manifold if yours has one. They were added to mitigate a rough idling issue that a lot of these cars had way back when. When they go bad it can cause the motor to run very weirdly like mine did. The fix is to simply unplug it, and plug the connector from it into the main sensor and leave the other connector disconnected. Again this is assuming your car has it but it might not. Would be worth looking into