rough idle, surging acceleration - tried some things, what's 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?

[DesktopDave]

I'd check the AFM.  Could be the temp sensors too, but your codes are clear.  What's the cam & crank resistance?  Crank hould be ~640 and ~1200 ohms for the cam.

[rojeho]

Check the AFM how?  Spray cleaner or something different?

[Nelson_40]

Check to see how freely the flap moves/look for crap on the sensor/meter wire.   If the top of the AFM box is damaged pull the top and check for condensation/corrosion/rust.  Might also check the connections for TPS and AFM.  Also worth triple checking all of your vac connections, a pain, but sometimes the answer.

What is your present idle speed?

[rojeho]

This one continues to elude me.

Idle speed is rock steady at 700-800 rpm.  You can feel a rough idle (periodic shake, shudder) but it doesn't show on the tach.

Since I replaced the vacuum hoses, it helped a bunch, but there is still a problem.

Instead of all of the time, now I get a hesitation when trying to accelerate from low rpm.  If I accelerate away from a light, shift at 3-4k, everything is fine.  The only problem is if I am steady state at 2000 rpm or so and try to accelerate.

Something new is that while stopped at a light the check engine light will flash on.  Most times it stays on for a couple seconds and then goes out.  Sometimes it will stay on, and the second I start to let the clutch out and change the engine rpm the light goes out.  It has not come on during steady state driving, or anytime the car has been moving.  Only when stopped and idling.  When it does this, the idle is normal - it doesn't change before the light comes on.  It's the dreaded vague 1222 code.

[Geoff]

mine did that with a slight vacuum leak. it stopped when I found the leak .   You may still have a sneaky one...
                                                 Geoff

[rojeho]

That's what I am afraid of.  Is there a definitive list of vacuum hoses?  I know that I skipped the one to the brake booster that I guess I need to do next, and then I need to spray test the intake gasket.