Video: Idle drop when AC compressor activates

[Hooty]

Over the weekend I completely removed the intake manifold/system and replaced the original 200k mile ICV with a new unit. I also replaced the VCV and checked for leaks with a smoke test. At first it seemed fine, but now my idle will on occasion hover around 1.5-2k rpms and surge. On some cold starts the car will almost completely die - I mean drops to about 200 rpm. The AC remains problematic on occasion. Any ideas?

New video from this morning:

https://youtu.be/58Wz5sP-qBU

First, thanks for your help!

I've read the dozens of threads pertaining to E36 idle drop. I don't think my case is "special", I am merely hoping that starting a newer thread about this issue might help me and others resolve their idling woes. Here's a link to the video I recorded yesterday: https://www.youtube.com/watch?v=ZGCqFHSTMKw

My issue: When the AC compressor kicks on, the idle drops low enough for the oil pressure light to flicker on the dash. This issue is most pronounced while in stop and go traffic, specifically while coming to a stop (clutching in, RPMs drop to idle). If I leave the AC on and idle for a while, this issue does not occur. Without the AC on, the car has no idling issues. Like many users on this forum, I can force the idle to dip slightly when turning on the headlights or depressing the window switch but the drop is not this severe.

This issue has existed since I purchased the car exactly one year ago and I have completely refreshed the intake/vacuum system. Installing an M50 manifold and new vacuum lines rectified the issue temporarily (perhaps the ECU was learning?) but it has since returned to the state in the video above.

Some things that I have done:

1. Removed and cleaned the ICV twice, valve moves freely (once before the M50 manifold, another while installing the manifold)
2. Replaced fuel injectors
3. Replaced spark plugs
4. Replaced all vacuum lines
5. Performed two smoke tests, *no leaks.
6. Checked grounds
7. Replaced oxygen sensor (CEL fixed)

Some thoughts:

1. *During the last smoke test I performed I noticed that smoke was spewing out of the top of my vacuum control valve (11747810831). I think this is normal operation if the valve is open at the time of ignition cut? Maybe I've just answered my question haha. Anyways, I bypassed the valve, no leaks.
2. I am thinking that maybe my ICV is just plain failing. It is original to the car and has covered 200k miles.

[samy01]

Why do you think you have an idle issue? I don't see your idle is unusually low. If there's a problem, it would be that your bearings are just not holding oil pressure that well anymore.

[blckstrm]

I'd suggest you look at one of the many "oil light flicker" threads - and also realize BMW states in the manual that this is a potentially normal situation.

I will note that my car started doing this around your mileage.

You will find this is actually temperature related. Yes, oil pressure is governed by rpm, but when hot, the oil thins enough that you get less pressure for a given rpm.

So when you let it sit and idle for a while, the auxiliary fan does its job and drops the temperature of the water first, which eventually cools the oil too, and you see the flicker eventually stop when the oil gets cool enough.

From personal experience, I only see flicker on old oil and after sustained water temps above about 205.

[Hooty]

I'd suggest you look at one of the many "oil light flicker" threads - and also realize BMW states in the manual that this is a potentially normal situation.

I will note that my car started doing this around your mileage.

You will find this is actually temperature related. Yes, oil pressure is governed by rpm, but when hot, the oil thins enough that you get less pressure for a given rpm.

So when you let it sit and idle for a while, the auxiliary fan does its job and drops the temperature of the water first, which eventually cools the oil too, and you see the flicker eventually stop when the oil gets cool enough.

From personal experience, I only see flicker on old oil and after sustained water temps above about 205.

I agree with you.

However, my issue does not seem to be solely related to oil temperature. My idle drops 200-300 rpm (according to my scanning tool's active monitor) as soon as the AC kicks on, as if I am releasing the clutch. With the AC off on a hot 90 deg. Nashville day in stop and go traffic, my idle is consistent, without drop, and the light will not flicker.

[Hooty]

Why do you think you have an idle issue? I don't see your idle is unusually low. If there's a problem, it would be that your bearings are just not holding oil pressure that well anymore.

The issue I am having is a significant drop in idle speed (200-300 rpm) when the AC is turned on. With the AC turned off, the car idles without issue.

[blckstrm]

If everything else is healthy it might be your compressor starting to fail - it could put enough load to drop rpm if it's dying. I replaced mine around 155k.

[RightYouAreKen]

This seems unlikely, but have you had your A/C system pressure checked? Years ago my A/C was a little weak, so I decided to "recharge" it with one of those auto store cans. I think I ended up putting a bit too much in and it caused a bit of idle droop when the compressor kicked on, and I could actually feel a slight drop in power momentarily while driving when the compressor kicked on. I took it to a shop and they charged it correctly and the symptoms went away. It was too long ago now to remember exactly how much it drooped, but it might be something to double check if you've recently had A/C service done.

[MParallel]

There is a coding option in the HVAC module to run a higher idle speed with AC compressor on.

Could be an option.

[projectDD]

I had the same symptoms in my first e36 m3. I tried everything and in the end rebuilding my vanos cured the idle dip. Has your vanos been rebuilt? I'm assuming that it has, given your car's mileage, but perhaps it's due again?

[Hooty]

Perhaps… but the VANOS was replaced about 40k miles ago. I don’t notice any power loss and can tell it is activating.