E30 Bucking/Stalling

[JLegleiter]

Ok, here is the scenario.

1989 325i

Main and Fuel Pump relays replaced in February.

In March:
Fuel Filter
Ignition Coil
Plugs
Wires
Dist. Cap
Rotor

C101 connector was removed and the harnesses hardwired together in February. Seems like overkill I know, but had you seen the condition of the connector it would make sense.

-----

This all began on Saturday. I was driving (naturally) and came to a stop light when the car died suddenly. It had not exhibited this behavior so I was concerned. The car restarted with some hesitation and I went on my way. Next stoplight, the same situation after idling for a few seconds. Gradually as I nursed it to my destination, it became more an more frequent. Initially it would die after as much as 30 seconds at idle, but eventually would die immediately after depressing the clutch and reaching idle RPM.

I was headed to a friend's. At the time this started I was nearer his house than mine, so it only made sense to go there, rather than attempting to turn around and head home.
I was there for a few hours, waiting for traffic to die down before trying to nurse my way back home. The car started, but cranked slightly longer than usual. Since the problem had only presented itself at idle, I took the highway home rather than surface streets to avoid stoplights. The problem did not reappear that night. I did have to stop at three or four lights on the way home, but did so without incident.

The next day, the car started, but again with hesitation. Made it to work without a re occurrence of the problem. On the way home however, while at cruising speed, the car will buck, and RPMs drop slightly, check engine light flashes, then power returns.

This is now becoming more and more frequent, and I don't want to drive anymore than I have to.

Here is the odd thing though, the only code than the computer spits out is 1263 - Evaporative Purge Valve. Now, from what I can tell, that particular fault should not produce these symptoms.

I have swapped in a spare DME I keep around, just to rule that out, without change. I have even disconnected the purge valve altogether just to see if that would produce a change in symptoms. It did not.

I have two thoughts at the moment.

The first being that the fault code produced by the DME and the bucking/stalling symptoms are unrelated. Perhaps the valve was already faulty and the DME has stored that code, but is not producing another code for the incidents of stalling.

The other is that somewhere in my harness there is a short, causing not only the stalling but also the to DME to read the fault incorrectly.

CPS keeps coming to mind, though I am baffled by the 1263 code being thrown.

Its one of those problems that could have nearly a hundred causes, but perhaps someone has experienced something similar. I searched, but have replaced nearly everything that had caused other occurrences, sans CPS.

Ideas?

[metalix1021]

A few of the symptoms sound like a dying alternator. The bucking on the freeway/CEL flashing.

[JLegleiter]

A few of the symptoms sound like a dying alternator. The bucking on the freeway/CEL flashing.

Alternator also checked in February. Brushes replaced.

[ethree]

I'd look into the cps as well as your afm?

[slo325i]

Just letting you know i have the same bucking problem as well.. please let me know if you find a fix

[jlevie]

Dying at idle tends to make me think of an intake leak. But loss of power while driving coupled with a drop in the tach makes me think of an electrical problem. So you might have two different problems.

A brief loss of power associated with a momentary dip and return of the tach could be:

1) A CPS signal problem. This will flash the CEL and usually sets a fault code.

2) Interruption of power or of the start signal to the DME. This will flash the CEL, but not set a code.

3) Interruption of power to the coil or loss of the grounding signal from the DME. The DME start signal and coil power are on the same circuit. So an interruption there can result in a flash of the CEL. A problem with the ground signal may or may not flash the CEL.

Another possibility would be bad connections at C191. That is the connector under the intake that routes the injector and temp signals from the engine harness. But I don't believe a fault there would result in a noticeable dip and return of the tach.

You have my sympathies as this sort of problem can be a maddening diagnostic effort. A random intermittent problem that can't be reproduced on demand is hard to find and fix. About all that I can suggest is that you check voltage at the coil, DME power input and DME start signal, which should be within a tenth of a volt of that measured at the power block in the engine bay. if one of those is significantly less than norm there's bad connection somewhere in that circuit.

[debacle]

Have exact same problem with my 1990. Has anyone been able to pin down this issue?

[jlevie]

After a two year struggle with this sort of problem over two race cars (the first was destroyed last year) I finally found all the things that caused it yesterday. The complete list of items that were contributors (as proved by diagnostics) is;

1) Bad CPS (passed ohms check but produced a distorted waveform)
2) Bad engine harness ( excessive leakage in the CPS coax)
3) Worn out engine with excessive play in the front main bearings that caused the harmonic balancer to wobble at high rpm
4) Corroded splice in the "hot in run & start" lead from the ignition switch on the first car
5) Weak coil in the main relay that couldn't hold the contacts closed well enough
6) Corroded fusible link
7) Bad injector electrical rail

Each time I found and fixed a problem I just exposed the next problem area. For most of this journey I had to rely on common sense and parts replacement. But now I have a RacePak IQ3 in the can and can selectively log data, which is how I found the last three causes in one day. Hopefully your problems won't be so hard to solve, but that list may give you ideas of where to look (in addition to the fuel system and AFM).

[sneville44]

My '91 Coupe had the same symptoms; random idle drop and pronounced momentary hesitation or bucking upon acceleration. The culprit was a faulty throttle position switch. Check out this Pelican Parts tech article:

http://www.pelicanparts.com/bmw/techarticles/JF-Tech/BMW_E30_3_Series_throttle_switch_replacement.htm

A new replacement completely fixed the problem!

[Maddog]

I had the same symptoms for the past 5 years with it progressively becoming more frequent. The following is what was done by me before I finally threw in the towel and had my 1988 325is towed to have Ryan Gangemi Motorworks in Auburn after Christmas; he found the problem and just informed me today it was fixed!

- New Main relay
- New fuel pump relay
- New OBC relay
- New TPS switch
- New fuel filter
- Refurbished AFM
- New CPS
- New ignition coil
- Repaired corroded C191 connector (check first since my wires were severely corroded; contributed to the problem but not the fix)
- Fuel purge valve
- Ran tests per Bentley to check ignition system; all good

In short, the harness for the CPS had a bad shield wire; the harness was replaced.

No way I would have figured this out. Ryan and his staff know how to troubleshoot and the reason I have had him do all of my large repairs and maintenance since I met him. I always leave his place knowing the job was done right.

Good luck since I know the feeling when it stalls on the highway or in traffic during rush hour.:SOS:

[b33mer]

Obviously an old thread but probably a recurring issue as these cars age. For my e30 the ICV/IAC was the cause. The stalling was associated with the throttle in a closed position (i.e. foot off the gas), at any speed. I didn't see mention of it above.

[ADEN]

What you described exactly happening to me if i pressure wash my engine bay but dissapear after like driving for 10 mins, sometimes stays until next day if i didn't drive much after the wash.
Until now i couldn't find a cause to this issue and didn't bother myself since it goes after 10 mins of driving.