Slight rough idle and surging acceleration - some tries - what next

[rojeho]

1992 318i, 110k. Slightly rough idle but not enough to really make the tach move. Intermittent surge on acceleration, usually between 2-3k rpms. Big surge and power rush at the end of it.

No codes, new plugs, checked the resistance on the coils, cleaned the ICV, replaced all of the vac hoses that I could see (valve cover to TB, two large ones off of the ICV, small diameter one for the intake runners, TB to FPR, medium one from TB to ? down near the strut tower).

What's next?

[weidner]

Me too... seems to be getting worse as the weather gets colder. Hmmm

Eyes on the road, hands on the wheel.

[DailyE36]

i had the same problem. the oxygen sensor was original so i replaced that and the problem is gone.

[weidner]

Fixed... Cost = $0.00

Give your brake booster vent line a wiggle. Mine had crimp-on hose clamps and they were loose. Took them off, installed traditional, screw-type hose clamps (see picture), and voila no more lean surge. Good luck!

[weidner]

I came up with a few other ideas as I was working on my car over the weekend.
- dip stick o-rings
- oil filler cap gasket

A smoke test would be next, I'd probably just do it and be done with it.
Good luck.

[rojeho]

Replaced the brake booster hose, no change. O2 sensor on the way, just to make sure.

Can I do a smoke test or do I have to take it somewhere?

[weidner]

Most shops can do this, and not too expensive... or you can build your own, there's several DIY threads on how to build a "homegrown" smoke tester.

Make sure to report back on what you find.

[eurotrash3x]

I am searching the forum for a solution as well, but mine is an m20 car. In my case, removing the oil filler cap FIXES the idle surge..? (help!?)