Dead spot in RPM range

[jlevie]

A jerking/bucking motion sounds like misfires. That could be from a bad CPS or bad harmonic balancer. Watch the balancer while you rev the engine. If there is any wobble, replace the part. If you don't see a problem there, replace the CPS with a new part.

[mrgraphics]

As a quick test (since I have two of the same sensor on the bell housing) I swapped the CPS and speed sensors. It ran, but idle was definitely worse. Engine seemed to shake. Same bucking action in the 2000-25000 RPM range.

Harmonic balancer looks good - no wobble.

[jlevie]

So replace both timing sensors with new BMW parts.

[mrgraphics]

Just ordered them. I took the car for a much longer ride on the highway and it actually was performing better at speed . . . so these sensors are definitely the issue. Just ordered from Pelican . . .

The existing sensors were Pick n Pull parts ($5 each) that I bought trying to diagnose why the car wouldn't continue to run. They served their purpose and showed that they were the problem, but 26 year old parts are probably not the best.

BTW - how critical is the speed sensor on an ETA? Obviously a bad CPS and it won't run, but what does the speed sensor do?

[mrgraphics]

New CPS - car pulls strong throughout the RPM range. Problem solved. It still has a bit of a stutter from a stop (press gas, slight hesitation, then it goes), but that's probably a tiny vacuum leak I'd suspect.

On a bizarre note, driving the car my engine started to shake. Got it home only to find my fan blades spontaneously broke off, leaving only 4. I've never heard of this happening before.

E30 - always something to fix.

[jlevie]

Broken fan blades will be from:

1) Worn water pump or clutch bearings that cause the blades to wobble.
2) The fan blades hitting the shroud because it is loose or not properly installed.
3) Bad motor mounts that allow the engine to shift and the blades hit the shroud.
4) A seized fan clutch.

[mrgraphics]

I think the winner is - #2, loose shroud.

When I went to remove the broken fan, I noticed that the shroud was not in the bottom tab on one side.

Bonus - my replacement fan is red, which matches the car :) I'm not sure why some cars had red fans, other's black. Seems to fit the same.

Thanks for the helpful advice jlevie.