AFM or not to AFM, that is the question

[Elmoperkins]

Hey all. 1st time posting here. I have been on 318ti.org trying to get some advise with no success. If you saw my knock sensor and under the intake project, then you will know kinda what's going on. here is a link...

http://www.318ti.org/forum/showthread.php?t=43020

I've got a cold start idle issue as well as an all around idle problem at all temps for that matter. The engine rpms are way too low and the engine will stall. Cold starts it fires after 1 to 2 seconds, then stalls unless I have my foot on the gas to keep the revs up. Same once at operating temp when rolling to a stop or sitting stationary.

I know the AFM has been tweaked by having the spring adjusted to smooth out the engine. This was pre vacuum leaks. Now that everything is sealed up tight, I have to make some AFM spring adjustments.

Also 1st time after finishing my project, I ran the car with the icv unplugged. It was the only way to keep the revs up without manually adjusting the throttle cables to keep the t body cracked open. With accessories on (a/c, rear defrost and lights) everything seems ok besides the cel for the icv. Power delivery was smooth all the way to redline, something I was trying to fix from the get go. It would bog down at WOT or seem to be struggling to give 100% power. 3/4 throttle would be max power if that makes sense with no hesitation or flat spot in the power band.

Today I plugged in the icv and made some adjustment to both the throttle cables and the spring in the AFM to keep the engine at a stable idle rpm of 800 ish. Every time the icv was connected, the engine rpms would drop severely and stall unless throttle was induced to keep it from stalling.

Now the idle seems to be at 800 rpm with no accessories on. I can add one load at a time and watch the rpms drop slightly. Once a/c, rear defrost and lights are on, the idle is down to 400 rpm and eventually stalls.

It's like the icv is not adjusting to keep the engine rpms at the target idle rpm. Like when it's plugged in. It goes to full closed which is a very small gap for air to travel through.

Also the flat spot in the power band is back in WOT situations.

At this point, I am unsure as to replace the AFM with a used oem one off eBay, shell out a lot of money for a new genuine AFM, or go reman from rock auto. OR convert to MAF, which from what i read is not very feasible if the car remains stock, which it will.

I have read out the status requests with ISTA and air flow is in spec at idle and the intake air temps are reading correctly.

Does anyone have any input on this? I really don't want to throw expensive parts at it and after all the repairs I did, I figured this thing would be running top notch. I feel like I'm at a loss ATM and not sure where to go from here.

Thanks for the help!

[DesktopDave]

Sorry I missed this post, welcome to the 'club!

I didn't have a lot of ideas, but it feels like your AFM is working. It might be under-reporting the airflow, but it's functional. I'd suspect some other component is causing the idle drop.
Have you tested the DME temp sensor or the A/C signal status line to the DME?
How lean is the car running open-loop? When it switches over to closed-loop, does the mixture remain pretty stable?
If the ICV is going to full close, the DME is compensating. It's attempting to enrich the mixture by shutting off extra air...that's why I'm suspecting some sensor is signalling a lean condition.
Do you have the DISA manifold?

[wazzu70]

Can you read the ICV position/duty cycle with the service tool? If so make sure that is rational. Also make sure OAT (outside air temp), IAT (inlet air temp), ECT (engine coolant temp), baro, ect all read rational. If one of these is off it can significantly impact your fueling which will cause stalling/bogging.

Other place I would look is for air leaks after the AFM. Best way to use this is use propane or similar around all the joints/gaskets. If you have a leak it will ingest the propane and rev up.

Check your intake elbow and intake manifold gaskets for common air leak paths