1988 E30 325i problem

Vacuum leak or an ancient distributor cap?

Bad or dirty injector?

Fuel filter is a good and cheap place to start, based on recent personal e30 experience.

thanks all, also, I find that the Oxygen sensor relay is missing...what is this means? I am trying to replace the relays there.

"Dean Dark" ¼¶¼g©ó¶l¥ó·s»D: snipped-for-privacy@4ax.com...

The only thing that would be relay controlled on the Oxygen sensor would be the heater power. There is a little heater built into most modern sensors to bring it up to operating temperature faster. The exhaust gas is hot enough to get the sensor up to temperature eventually, but for emissions purposes designers want to minimize the time that the engine has to run "open loop" (without O2 sensor feedback) during warm up.

Without the heater circuit you may get "check engine" faults occasionally about 4-5 minutes after a cold start.

I'm pretty sure that the '88 325i did not have a heater on the oxygen sensor. The reason that the oxygen sensor relay is absent is probably because it was never installed.

occasionally

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My '88 325is did have a heated (4-wire) o2 sensor. It's possible that the previous owner (or crap mechanic) fitted a non-heated (1- or 2-wire) sensor and removed the relay. Even my '86 535i has a heated sensor. Check the sensor and see how many wires it has. Replace the relay. If the sensor needs replacing, you might try the Mustang sensor trick. $40 vs $100-plus for the BMW version and the only difference is the connector.

Bill in Omaha '86 535i

Pardon my error. I see on Ebay that the '88 325i does have a four wire connector on the oxygen sensor indicating that it does have a heater.