3K rpm flat spot

[Hey_You]

I just replaced the spark plugs, wires, cap, and rotor. My 85' 318i still has a slight bobble below 3k, but above 3500 it runs perfectly smooth. However if I shift up and the RPM's land in the 3-3500 range, it's like the engine losses it's breath until it gets back up above it. Makes going up any hills even more terrible. I just picked up the car a few weeks ago, and other than removing my injectors and cleaning them, I'm out of ideas. Could it be that the timing is off?

[E30_Pare]

adjust your Idle control valve. I had my ICV turned all the way out and my car wouldn't gain below 3k. My idle seemed perfect though.

[Jean]

probably an AFM

[84driver]

I have the exact same issue. Have been reading that above ~3500 the AFM should be wide open and then fuel injection is adjusted based primarily on rpm. A sticky AFM would cause issues at lower revs.

I was previously suspecting my injectors (or something else with fuel pressure, pump or FPR) until I read up more on L-Jet. I'll report back when I get around to cleaning the AFM.

[EThirty318i]

probably an afm

x2

[84driver]

Yeah, here's another example of failing AFM from the same 318 that is in $500 turbo BFC thread.

I'll check the AFM sooner than later then.

[84driver]

From the above link:

Update for those interested...

I just check the AFM resistance circuit with an ammeter. Here's what I found

*No air: 412 ohm
*Build-up to 1/3 of full travel: linear rise to 900 ohm
*Then from there on, it slowly goes down to 600 ohm at full load, fluctuating about, keeping near 750 ohm most of the time.

AFM it is. Touche', M10, touche'.

My AFM is done too. My results:

No air: ~440 ohm
Build up to 1/5 of full travel: linear rise to about 800
then fluctuates wildly between 400 and 700.

This would definitely explain my flat spot issue.

[84driver]

Ok well it turns out that is NOT the way to be testing this AFM. Fix and writeup here: http://www.r3vlimited.com/board/show....php?p=2837806

[Hey_You]

Turns out that the problem was not cause by my AFM. I can't remember what it was, could have been from the faulty CTS or FPR. My AFM is/was fine. I also messed with my timing which could have fixed some things too. I will be going MAP sensor for the new setup though. No more mechanical air metering :)