m50 Idle Surging

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ten2doyle102
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m50 Idle Surging

Postby ten2doyle102 » Wed Mar 16, 2016 3:55 pm

Hey all...I am back... again. LOL!

So my track car has been suffering from a really bad rev hanging issue and surging idle. It will severely rev hang (meaning 5-10secs at a constant rpm) and surge from 1000rpm to 3000rpm. I know that this typically refers to a vacuum leak, but I simply can't find this thing if it is. I've swapped IACV's, ECU's, changed all the intake gaskets, replaced the connector on the bottom of the intake, swapped MAF's, the list goes on. It really only has 3 vacuum lines on it now... 1 from the IACV to the intake boot, from the IACV to the intake manifold, intake to the Booster and one to the FPR. All of these look good. Also, the injector seals are new as well. I am at a loss with it.... :( -angry- -lll._.-

I do know that it runs about 1000% better with the MAF unplugged... as a matter of fact I actually raced it like that last weekend it ran quite well. Seems to make plenty of power like this too. Starts right up as well. It does backfire into the intake at idle however with the MAF unplugged, but I figured that was probably normal, no?

Are there any sensors that would cause this behavior? It ran fine since the motor was installed and then after an event it got progressively worse.

Any ideas?
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Re: m50 Idle Surging

Postby Yoshi » Wed Mar 16, 2016 4:52 pm

There are 2 general big vac leak locations on M50s. The first is the pos connector for the CCV area. Mainly the connection at the valve cover. Maybe try plugging it and seeing if that changes things. The other one is the connector for the IAC at the intake manifold. The O ring or the clip itself breaks/fails and causes a permanent vac leak.

Got pix of your engine bay and that area? I can can point some thoughts to check. How's your brakes?
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Re: m50 Idle Surging

Postby M20_fever » Thu Mar 17, 2016 4:43 pm

Have you put a vacuum gauge on it?
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Re: m50 Idle Surging

Postby ten2doyle102 » Thu Mar 17, 2016 9:37 pm

Yoshi, I don't have the CCV operational at this point as it just goes to my catch can thingy and then vents to atmosphere. Meant to say that in the original post. Also, I just replaced the fitting that goes into the back of the intake too, so I don't think thats the cause.

Tony, I have not, but I'll try to to that tonight or this weekend. What is a good number for that? 20's?
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Re: m50 Idle Surging

Postby Yoshi » Fri Mar 18, 2016 12:24 pm

You just placed a fitting into the intake for the idle control valve? What did you do? I mean... without an ICV that makes sense. Same with the CCV. BMW motors idle like absolute shit if it has no CCV. Venting to the atmosphere creates a huge vac leak.
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Re: m50 Idle Surging

Postby ten2doyle102 » Mon Mar 21, 2016 3:10 pm

Sorry, I mean I replaced the plastic fitting that is on the end of the rubber hose that runs from the IACV and clips into the back of the intake. It came with a new o-ring on it as well so that's all new. The IACV is hooked up.

It ran fine before with the CCV disconnected as current;y setup, I can try replumbing it though to see if anything changes. I got the motor this way actually. Not sure how it could cause a leak since everything on the intake is plugged.

Sorry if I am not describing things very well.. lol!
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Re: m50 Idle Surging

Postby M20_fever » Fri Mar 25, 2016 8:57 pm

18-20" at idle is normal for most stock engines. You also need to see how it's holding vac. Is the needle bouncing, surging, does it drop when you pop the throttle?
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Re: m50 Idle Surging

Postby ten2doyle102 » Wed Apr 06, 2016 3:36 am

Alright....so I've done some more testing and have a few things to report. The first on is that I found a small coolant leak while testing.... the more important item is I did some testing with my vac/boost gauge that I had laying around. I assume this should atleast get me somewhat close vacuum readings, no? Anyways, so for the amount of vacuum it has... well... there is none. It reads around 3 inHg on the gauge at idle. Sounds awfully vacuum leakish... This is my first time playing with stuff like this, but correct me if I am wrong, but with the gauge connected to the intake, if I blip the throttle it should go to 0 or maybe just past for a second, correct? In this case it actually gains vacuum when I blip it. Seem correct? I've been watching a few videos on using vacuum gauges to see what's going on with the motor. and nothing was mentioned about that occurring. I also thought maybe the gauge doesn't react fast enough to changes in vacuum so I am going to order a actual vacuum test to try and see if anything else becomes apparent.

If if is a vacuum leak, man, I just don't know where it is. The only thing I don't think I replaced were the injector seals.... though I can't remember for sure. We did spray some starting fluid around the injectors and did not hear any noticeable idle variation. Can bad compression do something like this??? It runs so well and makes good power (with the MAF unplugged) so I just can't see if being a timing or a compression issue.

This is quite frustrating.... lol
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Re: m50 Idle Surging

Postby Yoshi » Wed Apr 06, 2016 5:35 pm

Video? I don't remember... At idle you should pull a decently strong vac. I deal with psi/bar so hgin isn't my bag of tea. But vac should be strong. You should hit 0 when flooring it.
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Re: m50 Idle Surging

Postby M20_fever » Thu Apr 07, 2016 12:29 pm

massive vacuum leak post MAF. Spray starting fluid down around the the manifold gaskets. Not too familiar with 24v but on an m20 i would be looking at the bitch tube so if there is something similar on 24v look there. TBH at 3" at idle I'm surprised it runs at all, where are you pulling the reading from? If that reading is accurate a smoke test should make it very obvious where the leak is.
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Re: m50 Idle Surging

Postby Yoshi » Thu Apr 07, 2016 12:33 pm

M50s have shit connections for the idle control valve. But otherwise, they are pretty bulletproof honestly. There's so few vac connections. I love it.
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Re: m50 Idle Surging

Postby M20_fever » Thu Apr 07, 2016 12:41 pm

Don;t they have plastic intakes? Seems like a little to much torque on the intake bolts could crack it, no?
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Re: m50 Idle Surging

Postby ten2doyle102 » Thu Apr 07, 2016 2:18 pm

I have sprayed starting fluid everywhere on this thing and the idle never waivers. I'll try again tonight or tomorrow though. Like you said, with a vacuum leak that big, it shouldn't be the freaking hard to find... Also, we just redid all the intake gaskets and throttle body gaskets with no change. This also involved thoroughly inspecting the intake for cracks and I couldn't find one. Also, the connector on the back of the intake is new with a new o-ring. Should be good there.

I am equally confused on this one.... argh!
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Re: m50 Idle Surging

Postby Yoshi » Thu Apr 07, 2016 2:23 pm

I've never seen an intake crack. They have metal retainers to keep you from over tightening the mani bolts. I think you need a smoke machine brah.
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Re: m50 Idle Surging

Postby ten2doyle102 » Thu Apr 07, 2016 4:27 pm

I don't know anyone around here with one anymore... might invest in one, no any good brands??? Maybe I could find a few hipsters to vape the heck out of it.... lol. (no offense to anyone that does that... lol!)
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