1991 535i/5 acceleration/power problem

[240deluxe]

Guys, I have finally FIXED this issue! Before I say what it is, I'm going to go over the symptoms again so the next person can easily read this (or skip below).

Car: 1991 BMW 535i (E34 with M30B35 motor).

Symptoms: Car originally runs great and normal.

Day 1: Hard to build RPM's when you're releasing the clutch (I don't know how it behaves on 4HP22 [auto] cars - probably hesitation from a start).
Day 2: Same symptoms as Day 1, but your acceleration feels very impeded/hindered, feels like you have 50% less horsepower.
Day 3: Same symptoms as Day 2, but your car suddenly runs like shit. Idle is rough (heavy misfires) and it's impossible to build RPM's past 1,500 even if you're flooring it. Car may suddenly behave normal again, perhaps for even the rest of the day.
Day 4: Same symptoms as Day 3, but the car REALLY feels sluggish and its incredibly hard to build RPM. Car may suddenly behave normal again.
Day 5: Had trouble starting the car, car runs and idles like absolute crap, almost impossible to drive (especially on a manual trans car, hard to build RPM's). However, it may momentarily run normal again, but return back to running poorly.
Day 6: Car will barely start, idles at 400-500PM (very poorly), if you try revving it, the car will violently misfire. It's so violent that it grenaded my cat and blew my airflow meter right off the intake manifold (wasn't tight enough, my fault).
Day 7 and beyond: Car runs worse than ever, misfiring like crazy, and backfiring both in exhaust and intake manifold (lots of unburnt fuel sitting around because lack of spark). Now, the car will rarely/never run normal again.

What the issue was: A $1 part, amongst other things. And yes I did say ONE dollar, and even as low as 86 cents in some cases. This part was called the Woodruff key, which is a semi-circular piece of metal that (to my understanding) helps align the nut that holds the harmonic balancer/crankshaft pulley. Mine was bent/sheered/twisted/torqued. And by the way, this nut is the same as an axle nut for the same car, it has the same part number, and make sure its torqued to around 300 ft. lbs. My nut was loose, the previous owner did a shitty job assembling this and therefore it was loose. These two factors cost less than $5 (five dollars) all together, and they allowed my harmonic balancer to move around just enough to give my crank position sensor a hard time reading the teeth on the harmonic balancer, thus giving me terrible spark issues. So, make sure your harmonic balancer nut (axle nut) is tight, make sure the Woodruff key is in good shape, and make sure your harmonic balancer/crankshaft pulley don't have any play.

Troubleshooting: Before you pursue this culprit, do the proper troubleshooting. Do a compression test, oil pressure test, vacuum test, pull your spark plugs and inspect them, etc. I did all of this and everything came back good. Oil pressure was around 40 psi, compression was about 150 per cylinder. Then I started throwing parts at it like an idiot. I put a new crank position sensor, ignition coil, spark plugs, distributor cap, distributor rotor, fuel pressure regulator, remanufactured fuel injectors, remanufactured airflow meter, remanufactured ECU/DME. I was also afraid that the fuel pump was sending fuel at good pressure (40 psi) but not enough quantity, so I was ready to spend more on a fuel pump and filter. I was also going to try plug wires, cylinder #6 reference sensor, etc. I'm glad I took it to a VERY GOOD mechanic and he found this problem in no time.

I've learned a lot from this 4-month nightmare and I got a lot smarter from this piece of shit E34. At least it works, for now.

[Jesse535i]

My automatic 1991 535i had the same acceleration problems. lack of power or RPMs at low speed..
After replacing the plugs and plug lines-
I finally had luck with the Distributor Cap & Rotor (my cap was was cracked).
I would check the cap & rotor, just to make sure they're not burnt out.