This #$%^&*@ car! long post

[Ross]

Looking for suggestions from good diagnostic mechanics.
'95 525it M50 vanos auto. The trouble is an off idle stutter and hesitation and little power until the revs climb a bit. Even without load in neutral when the throttle is snapped open there is a tiny lag, bwaa then at around two grand it zings right up. The low range is for ****.
My efforts so far;
Checked for vacuum leaks, none.
Cleaned throttle body and checked for smooth opening(OK), no change.
Cleaned IAC, no change.
Changed o2 sensor(had code,sensor was <20k), no change.
Checked plugs and connectors, looked good.
Injectors ultrasonic cleaned and flow tested, one had the pintle stuck open and was replaced w/new Bosch, second examination of the spark plugs showed one was rich.
All spark plugs replaced along with fresh injectors. The stutter it had off idle now gone but hesitation persists.
Cleaned MAF, no change.

If someone else were to present this to me I'd suggest vacuum leaks. I've looked and looked again, none found.
I haven't thrown things at a car in a very long time but am coming close. Can any of you guys think of WTF I'm missing here?
EDIT The TPS was also changed, first thing I did after checking for vac leaks.

[Tiger]

Cat Converter clogged? Crank Position sensor... or MAF.

[attack eagle]

subscribed

[yaofeng]

Throw 6 ignition coils at the car. You've got a few E34's. Use them.

[bmwrp8]

try removing the cat for awhile and take it for a spin in the block...see if it had changes...might be a bad cat if not....fuel lines , f.pump , coil packs...

[BimmerMeUp]

Throw 6 ignition coils at the car. You've got a few E34's. Use them.

+1

My problems were very similar to yours and coils fixed them. Now if I could just fix the A/C.......

[markus]

buddy had a similar issue with his 94 325i. He had a bad coil pack. Sounds llike thats the case to me.

[ryan roopnarine]

busted diaphragm on the fuel pressure regulator? pull the vacuum hose off of it and see if it smells of gasoline.

if you aren't willing to swap coils, wrap the ones on the car in strapping or duct tape and see if an improvement results.

[Ross]

Thanks for all the ideas guys. I will investigate them all. Looks like the "new"E39 will be donating some parts for experimentation.
I hate to be a parts changer but I'm running out of ideas.

[Ross]

UPDATE
Connected a vacuum gauge to check for restricted exhaust. Steady 19" at idle, recovers to about same when throttle held open and steady RPMs. No restriction
Checked fuel pressure regulator operation simply by disconnecting and plugging source, pressure rise causes idle speed to increase.
Swapped known good MAF from the 530(same#), no change.
Swapped six coils from 530, no change.

There is a spark knock when the throttle is snapped open as well.
What are your automatic M50s like off idle when the throttle is snapped open from idle?? Jon, you don't count.
My E39 is a whole different animal compared to this one but I'm beginning to think it's the nature of the beast. ??
EDIT The next test will be for absolute fuel pressure. I need to rig a gauge as mine is intended to read from a schrader valve. 123k on it, fuel pump could be tired. It's quiet but who knows. Will advise.
Bloody good thing I have a "parts" car.