Intermittent Driveability Issue

[tezmanian]

1995 318i e36 intermittently "bogs down" under any and all operating conditions--no one condition (e.g. cold, warm, idle, acceleration, steady speed) seems to inspire onset. Can "drive through" this apparent complete loss of power condition by gently reducing then "massaging" throttle while disengaging clutch. Engine eventually returns to normal. Where this a 1950's car, I would suspect a fuel mixture problem--probably too rich or too much choke.
At onset, vacuum decreases.
Under all operating conditions temp gage is never in the standard BMW straight up position--only warms to about 1/2 way from cold to vertical/normal, and sometimes does not remain steady--may decrease then rise to aforementioned approx 1/2 way position.
Independent repair shop replaced cat converter, mass airflow then, when unable to correct this problem, took it to local BMW dealer for help. Dealer noted: "fuel pressure normal, initial GT1 readings indicated all sensors were way out of spec...400*F engine temp, no cam sensor, no throttle switch, no injection signal, etc, but engine was running! Faults for both rich and lean conditions recorded so far. Drove with GT1 hooked up and vehicle never failed during drives, ran sluggishly occasionally, but only momentarily."

That "momentary" sluggishness is the issue. It's really more than momentary and its onset is completely random and unpredictable.

Independent shop got the car back with this problem unresolved. Shop says there are no stored codes. I do not have a code reader, and no codes are presented in the instrument display.

I have tried substituting a good relay for the DME relay which confirmed that the DME relay is good, i.e., problem presents itself with either relay.

Any ideas on what I can do to troubleshoot and repair? Both independent mechanic and BMW have given up.

[coolbear1]

Haven't had much experience with 318, but I have had a similar thing happen, and it drove me crazy.
My 325 was doing the exact same thing.
After testing and changing everything in the world, the car did me a favor, and refused to start one day.
I'm almost embarased to say it was a bad ground cable that grounds the motor to the chassis. I was intermittantly loosing sufficient ground to the engine for it to run properly, but just enough ground to keep it running.
Most likely not whats wrong with yours but worth checking.
The motor ground cable on a 325 is located just above the inner ball joint next to the passenger side motor mount.

good luck.

[Jeron]

Definitely sounds like a wide spread electrical issue. It would be nice if it was a grounding issue. Go ahead and check the running voltage as well. Could be the ECU.

[tezmanian]

No joy yet. Newly discovered symptoms during troubleshooting attempts today:
-airbag light stays on for about 5 minutes after start up then goes out.
-check engine light comes on when poor running condition occurs (shouldn't that leave codes?).
-Thermostat checked out okay.
Still hoping this thing will be drivable again.

[tezmanian]

Stomp test result: 1222...many times. That checks with the drivability condition (O2 sensor detected very lean or very rich for more than 10 seconds). The diagnosis for that error does not seem too definitive, i.e., O2 sensor or something else. The BMW invoice for the failed repair attempt included this line item: B SIB #11-03-98 RECALL 98E-A02 O2 SENSOR HARNESS 0051364 INSP O2 SENSOR - NO FURTHER ACTION REQUIRED NWD NO WORK DONE AT THIS TIME. Any suggestions for next troubleshooting step?

[Jeron]

CEL with no code and intemittent bogging can be O2.

[tezmanian]

Fixed...finally. Great indy used patience and the right diagnostic equipment to get accurate read of the transient condition. Turned out to be a bad O2 sensor--intermittantly shorted (internal fault) causing erroneous "too rich" message to ECU resulting in temporary fuel starvation. I am told that O2 sensor should have been replaced when cat was replaced to avoid this. Thanks to all for help and suggestions.

[Jeron]

Glad you got it fixed.

What about the temperature gauge/ thermostat issue?

[tezmanian]

Next project. Suspect it's either bad gauge or sensor, but it does not have anything to do with driveability.

[Jeron]

Thermostat is way more likely than gauge or sensor. Good luck.