More idle issues after firing parts cannon to fix original idle issues

[Bdc101]

Help me out with this problem which is proving to be extremely stubborn.

Earlier this year I saw my unstable idle problems come back, with some symptoms of the car dying at stop lights when idling in neutral after along drive (it's a manual transmission so it would only happen in neutral). It was an occasional problem I had seen before but thought I had fixed it after cleaning out the ISCV real good.

A few drives after replacing the starter (unrelated problem, the original starter solenoid started clicking when I would try to start) I saw an engine failsafe prog happen when taking the family out for a mother's day hike. The only code was idle speed valve mechanical fault.

Since we are about to sell this car (we just bought an E70 diesel to replace it) I figured, let's fire the parts cannon and make sure we fix the problem rather than let it drag on, replacing parts one by one. So I replaced the ISCV, the MAF (always seems to be a suspect even though it tested fine), and the DISA valve (which had been repaired last year but now had a torn diaphragm). When I took it apart I found a tear in the intake elbow, so I replaced that too. (That was probably the original problem all along, and it had probably torn when reassembling after replacing the starter since I had had it off.) I also replaced the throttle body gasket.

Got it back together for the first time, and it threw idle speed plausibility codes repeatedly, with a high idle, about 1,200 rpm. Figured I hadn't reassembled it right, so I took it all apart and put it back together real careful like. After I put it back together, it seemed to idle high still but solid until I took it for a drive. After I gunned it, the idle started surging from 1,200 to 1,500 rpm repeatedly.

At the advice of this board I took it apart yet again and triple and quadruple checked that I put it back together right. And this time, it idled super solid at about 700 rpm, even on the first half of my test drive, until I gunned it again after which it started surging even more severely from about 1,200 to 2,000 rpm. It went into engine failsafe again and threw the same "idle speed valve mechanical fault" code (no other codes present). Which, the crazy thing is, it drove great for the first half of the test drive, and didn't have the clunkiness associated with a vacuum leak at all. But after it started surging it became clunky again.


Do I have ANY other things to check or try other than buy a smoke tester or pay an indie to smoke test it for me?

Lastly... the throttle body seems to be fine, but when I took it out I notice that it's not fully closed when it is at rest. I can push it fully closed with my finger but it doesn't stay closed. And the other question I had, on the ISCV, the arrow is supposed to point INTO the manifold, right?

Any help is gratefully appreciated as I am at wit's end with this car.

[Bdc101]

Follow up with some things I remembered:

1. I cleared adaptations several times.

2. I did not replace the ISCV gasket in the intake manifold. I will order one on my next parts order. The old one seemed fine but I did not remove it from the manifold to inspect closely.

3. I swapped back to the old MAF with no change in symptoms so I am going to return the new one. Rockauto will take it back even if you have installed it, as long as it looks new.


4. Newtis unfortunately doesn't confirm the orientation of the ISCV: https://www.newtis.info/tisv2/a/en/e...vernor/BljAF97

[80stech]

Did you use any carb cleaner on the IAC valve or throttle body? Throttle body needing help to close is a big red flag.

[Bdc101]

No, I did not clean out the TB except wiping it down with a towel.And I just treplaced the IAC valve.



I do see that the newtis procedure shows the IAC in the upside down orientation to how I installed it. I installed it with the arrow on top pointing into the manifold. I am not 100% sure that is how the old one came out.

[X5chemist]

If I remember correctly, the TB black motor cover is forward facing to the radiator. The connections points to the firewall.

Reference pics: https://xoutpost.com/bmw-sav-forums/...verhaul-3.html

[80stech]

That might be it! I didn't think it could be installed either way but good to know because I have mine apart

I just had a look at my throttle body and it is was open just a hair so that must be normal.

[Bdc101]

Originally Posted by X5chemist

If I remember correctly, the TB black motor cover is forward facing to the radiator. The connections points to the firewall.

Reference pics: https://xoutpost.com/bmw-sav-forums/...verhaul-3.html

Yeah, the throttle body I think can only go on that way, but the IAC valve right above it is what I am wondering if I might have gotten on backwards... see the newtis link above.

Originally Posted by 80stech

That might be it! I didn't think it could be installed either way but good to know because I have mine apart

I just had a look at my throttle body and it is was open just a hair so that must be normal.

OK, thanks for checking... it doesn't seem like it's loose to me but stranger things have happened, right??

[Bdc101]

I took it apart again (getting really good at it now) and verified that the IAC valve is indeed oriented in the correct position. The arrow points into the manifold.



I started it up and it idled rock solid, starting about 1,000 rpm when cold and decreasing to 700ish but it didn't surge at all. Then after it was warm I blipped the throttle a handful of times and it started surging after a while of doing that.


At this point I'm out of suggestions - going to take it to the indy to have a smoke test done.

[Effduration]

Virtually all these 20yr old BMWs will benefit from a smoke test...So yes go get a smoke test, preferably by someone who knows the M54 engine. There are like a dozen possible sources of a vacuum leak.

[X5chemist]

Mine had a high idle after an oil change. I freaked out. Finally, I noticed the oil dipstick was not inserted all the way. Pushed down and idle returned to normal.