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Discussion Starter · #1 ·
Hey guys,
I searched around for a bit looking for a thread about an ICV Delete thread using the MS43/42. Didn't find much, more specifically I didn't find much regarding the 2.5L m54b25 engine. So here are my findings.
Firstly My car has an M50 manifold upgrade and i'm not sure how that has affected my results for this test, but do take it into consideration. I'm also doing this on an automatic 2001 325ci.
My method:
Disconnect and block off the ports to the ICV on both the intake boot and ICV valve.
Unplug the ICV valve connector
Grab out a laptop with all your MS43 tuning goodies and sit down.
For a tune to code out the ICV valve i looked to the MS4X wiki, I did indeed find a tune but it said specifically it only worked with the 3.0L engine. (Due to a different sized throttle body)
I said F**k it and tuned the parameters onto my DME. Firstly the car did run and it did start. It was a little rough at first but it had a very stable idle. Only "hunted" when AC came on or off, Put it into drive, or rev'ed it. But mind you it always stabilized after a few seconds. To counter this i simply bumped the idle speed under all conditions to 850RPM. This helped the idle smoothness tremendously. It wasn't too high and didn't annoy me.
At first the car was a little bit annoyed when slowing down to a stop it would "hunt" again for a few seconds before stabilizing. Also I found that when giving very little throttle (like 2% by hand on the pedal) it sputtered like an angry dirt bike before reving up. That only usually happened when it was a cold engine and did happen once when I set off in drive.
Now the conclusion, it has been easily over 2 weeks since i did the delete and i now plan on completely removing the ICV. (Not just blocking it off)
The reason is because the car behaves almost identically to how it did before. I'm assuming this is because the car has learned and adapted some things. It doesn't "hunt" at all, doesn't care when the AC comes on or when its put into drive.
It has noticeably improved throttle response from a stand still. The car feels a lot more "on it" when you punch the gas as it doesn't have to open up the little ICV before the big throttle plate starts opening.
My favorite feature is the induction noises though. As the big throttle plate opens as soon as you punch the gas you get this very satisfying little vacuum noise as air rushes into the intake.
If you have a 3.0L engine just go for it follow the guide on the MS4X wiki and see how you like it. disconnect and plug up the lines and if you don't like it just return it back to normal.
If you have a 2.5L i would still go for it but bump the idle speed up to 850RPM.
In both cases I would drive it for a week before changing it back. Just so the computer can learn a little and adjust.
You have nothing to lose folks except a couple hours of time.
To be completely honest i forgot i even did it until i checked my engine bay yesterday and saw the line plugged up:rofl: That is how seemless it is.


Tune your DME at your own risk. It is possible to brick it when uploading a tune if done incorrectly. Please read up as much as possible and learn how to do it before hand. And above all else keep a stock tune of your DME safe if you ever need to go backwards. Cheers

Premium Member
E30M3 Race F10 535 R1150Rt M Coupe
11,388 Posts
Detailed enough of a test, thanks for that.

A thought or two; I'm unsure of the DME operations for the various iterations of the M45 engine, but I do know that the idle valve plays multiple roles of not only idle control but also overall air management into the engine.

Starting with engines as early as the S14 & S38 the idle valve would open completely on WOT. Fast fwd. a couple of generations of DME and the idle valve would be first in line on tip in to smooth things out but also going full open on WOT, so that the engine could gulp that few more CFM of air (via the valve) when needed. Then there's the compensation factor during A/C operation.

Has anyone done some deep testing to know if with a factory tune does the ICV go full open during sustained periods of WOT?

I suspect so, given the increase in noise you hear as the air (seemingly?) is only entering via the throttle plate.
For 90% of normal driving the change in air filling is superfluous.
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