RPM's dipping below idle speed

[Newjack]

I've noticed a weird problem with my car in the last couple days. Let's say I am driving in 4th gear at about 45mph. If I clutch in and put the car in neutral the RPM's will drop. The problem is that when the RPM's drop, they drop below the idle speed. Sometimes when this happens my RPM's will drop to 500 and nearly stall the car (The car starts to shake a bit). It doesn't do this at every speed and it seems to be more common when my RPM's fall from 2000 or higher. For example this problem won't really happen if I am idling and tap the gas for a sec to 1000rpms, they will float down a hair lower than idle and float back up.

Car is a 2005 manual. OE fuel pump, OE fuel filter. DISA has been rebuilt with G.A.S. kit within the last 3k miles. Lower intake boot replaced recently as well. ICV cleaned thoroughly in the last 3k miles.

Any suggestions? Justin Hornung mentioned it might be the camshaft position sensor.


Made video. Sorry for the quality, it was raining and driving a manual while recording is not easy.

https://www.dropbox.com/s/pi3kgu153y5ir93/2013-12-15%2001.04.56.mp4

[Johnmadd]

Upper intake boot?

[echo46]

Any cracks in associated CCV hoses? CCV getting clogged. When was the last time you changed your fuel filter?

[Newjack]

Any cracks in associated CCV hoses? CCV getting clogged. When was the last time you changed your fuel filter?

No cracks in any CCV hoses. CCV and all associated parts were replaced last winter. There might be a little mayo inside due to the short trips and cold weather we have been having. Need to take it for a long drive.

Sent from my Nexus 4 using Tapatalk

[Newjack]

Slight update. Its almost 60° here today and the car seems to act a lot more normal. RPMs still dip a teeny tiny bit buy its hardly noticeable. Going on a road trip tomorrow and will get the car nice and hot. Maybe I have some BMW mayo that is causing this who knows.

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[Avetiso]

I have a similar issue, but it has stalled my car multiple times and often drops to 500rpm, engine starts to shake. Cleaning my ICV and fixing DISA helped a little, but still there.

Looking to do VANOS on Saturday, hoping that helps. If not, it's catch can time. Goodbye CCV.

[echo46]

If you just replaced the CCV, I would think its good. Did you go with the cold weather one? You could also check the fuel pressure at the rail. Any codes?

[Newjack]

If you just replaced the CCV, I would think its good. Did you go with the cold weather one? You could also check the fuel pressure at the rail. Any codes?

CCV was replaced about a year ago with the cold weather version. My commute to work is very short. Most times my car is barely warmed up when I turn it off. These short trips cause inevitable BMW mayo to build up and the only cure is to drive it for a while and get the motor nice and hot.

How would I go about checking fuel pressure? Would a failing fuel pump shoe any signs of failure? Or is it like a clutch and you don't know when it will fail until it fails?

Vanos has also been done.

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[danewilson77]

Should be a Schraeder valve on the fuel rail.

It's not a toy, it's a Droid > Sent from my S4 > Mason, OH

[LivesNearCostco]

How do you attach a fuel pressure gauge to the Schraeder valve on the rail? I was just looking at the fuel pressure test gauges from Harbor Freight, AutoZone (Actron), and O'Reilly Auto. Most of the fittings seem to be clamp or hose fittings... maybe the standard fitting just screws onto the Schraeder valve?

[Johnmadd]

Vacuum leak somewhere, maybe a loose connection from your last time doing the boots.

[echo46]

Yes, could be a vacuum leak. Go over all boots, hoses, tubes etc for cracks and attachments. I mention fuel pressure in case the fuel filter or a fuel line is clogged. I really don't think you would be having CCV issues only a year into a cold weather replacement.

[LivesNearCostco]

Could try that "spray the starting fluid" trick while engine is running to look for leak, or pay a shop to do a smoke test.

How many miles? With original fuel filter and original fuel pump, could be one of those is holding up gas delivery at idle, but the fuel pressure test would show it.

[Newjack]

108xxx miles. Just drove it about 2 hours one direction last night and 2 hours back home. BMW mayo should be gone, it is also warm here.

The problem still persists, and when I go from cruising in 6th gear to neutral car hits below 500rpms hard. I don't think its a vacuum leak, boots were inspected and replaced not long ago. ICV cleaned and DISA repaired with G.A.S. kit. Problem only started happening recently. I'd bet its either the fuel filter or fuel pump. Really not looking forward to replacing either of those.

[echo46]

Both are very easy jobs. I'd start with the fuel filter as that is cheaper.

[ryankokesh]

Anyone figure this out? Having the same problem, but more so when everything is up to temp. Release the clutch in neutral and RPMs dip below idle.

Recently replaced:
- CCV
- Fuel pump
- Fuel filter
- GAS DISA rebuild

Can't find any vac leaks or anything.

[wsmeyer]

On the back of the intake manifold there are two ports capped off, check and make sure those haven't cracked. #'s 15 and 17:

18346

[Dave1027]

On the back of the intake manifold there are two ports capped off, check and make sure those haven't cracked. #'s 15 and 17:

My intake manifold had three ports back there. One large and two small. For me, it was the large cap that was badly cracked.

http://www.bimmerforums.com/forum/attachment.php?attachmentid=525911&stc=1

[wsmeyer]

Interesting. I only saw 2 on mine. What does realOEM show for your year?

[Dave1027]

Realoem shows only two ports for mine but it's not correct. It without a doubt has three. I just did that job two weeks ago. It's just like the pic I posted. How did you physically checked yours? Pulled the manifold?

[wsmeyer]

Yeah I had my manifold off for CCV swap and cleaning and I only noticed 2. Hard to imagine I missed one but possible.

Your pic isn't showing for me on tapatalk

[ryankokesh]

Appears I have 2. Not a damn thing on either of them, but there's definitely two there. :dunno

[Dave1027]

Appears I have 2. Not a damn thing on either of them, but there's definitely two there. :dunno

Not a damn thing on either one? They should all be capped with rubber caps. I don't see how the engine would run without those ports being capped.

[wsmeyer]

Appears I have 2. Not a damn thing on either of them, but there's definitely two there. :dunno

Capping those would be my #1 priority. Maybe they don't go anywhere on your manifold but it would be pretty cool if your engine ran better for about $1

[LivesNearCostco]

Wow I never knew these were on the back of the intake manifold. Is it possible to check them by feel without removing the manifold? Eventually I will be removing my manifold to inspect/replace the hard coolant pipes, but not sure when that will happen.

Besides checking for vacuum leaks, it might be a good time to inspect/clean the ICV if you haven't done so in the last 2 years. A gummed up ICV could do this if it opens too slowly when you let off the gas and the throttle body closes.

If not CCV, vacuum leak, or ICV, maybe need a VANOS piston rebuild with new seals?

[Vas]

What about the ICV grommet? it is pushed into the intake manifold and creats an air tight seal for the idle control valve. It could be causing a vacuum leak there.

[ryankokesh]

Not a damn thing on either one? They should all be capped with rubber caps. I don't see how the engine would run without those ports being capped.

Lol, apparently it runs fairly well. Grabbed some caps at the parts store. Hoping for the best!


Capping those would be my #1 priority. Maybe they don't go anywhere on your manifold but it would be pretty cool if your engine ran better for about $1

Actually $2.69... but who's counting ;)


Wow I never knew these were on the back of the intake manifold. Is it possible to check them by feel without removing the manifold? Eventually I will be removing my manifold to inspect/replace the hard coolant pipes, but not sure when that will happen.

Besides checking for vacuum leaks, it might be a good time to inspect/clean the ICV if you haven't done so in the last 2 years. A gummed up ICV could do this if it opens too slowly when you let off the gas and the throttle body closes.

If not CCV, vacuum leak, or ICV, maybe need a VANOS piston rebuild with new seals?

Yeah, you can check them by just taking the air filter holder majigger out. ICV was cleaned fairly recently, but heck why not do it again. VANOS was done a year or two ago.


What about the ICV grommet? it is pushed into the intake manifold and creats an air tight seal for the idle control valve. It could be causing a vacuum leak there.

Replaced that bugger recently... think when I did the DISA?

[Hornung418]

Yeah I had my manifold off for CCV swap and cleaning and I only noticed 2. Hard to imagine I missed one but possible.

Your pic isn't showing for me on tapatalk
There should be three. one is for the Exhaust flap that normal 330's have (It should be capped on a ZHP), one goes to the other side of the manifold and has a check-valve on the front, That goes directly to the CCV (which should also have a cap on the port), the last one goes to the Secondary Air Pump, Unless you have headers, that should have a vacuum line connected to it.

[Dave1027]

There should be three. one is for the Exhaust flap that normal 330's have (It should be capped on a ZHP), one goes to the other side of the manifold and has a check-valve on the front, That goes directly to the CCV (which should also have a cap on the port), the last one goes to the Secondary Air Pump, Unless you have headers, that should have a vacuum line connected to it.

All three of mine were capped with rubber caps on them. One large and two small.

No lines going to anything.

[Hornung418]

All three of mine were capped with rubber caps on them. One large and two small.

No lines going to anything.
Do you have catless exhaust primaries?

I plugged all of my ports when I installed the performance headers.

[Dave1027]

Wow I never knew these were on the back of the intake manifold. Is it possible to check them by feel without removing the manifold?

Yep. I replaced my rubber caps by reaching around the back of the manifold. I did have to remove the shield around the brake booster to easily get my arm in there. You cannot see the ports. Go by feel only. To remove the plastic shield I also had to remove the airbox, intake boot and cabin filter assembly.

[Dave1027]

Do you have catless exhaust primaries?

I plugged all of my ports when I installed the performance headers.

No. As far as I know it's all stock. Are we talking about the same thing? I'm talking about the three ports on the back of the intake manifold facing the firewall.

[Hornung418]

No. As far as I know it's all stock. Are we talking about the same thing? I'm talking about the three ports on the back of the intake manifold facing the firewall.
You should have a line running from the manifold to the SAP valve. That's connected to the cylinder head. It should have a black and white one-way check valve connected to it with an electrical conection.

[Dave1027]

You should have a line running from the manifold to the SAP valve. That's connected to the cylinder head. It should have a black and white one-way check valve connected to it with an electrical conection.

Is it possible I have it already but it's connected to a different port located somewhere else?

How about other owners? Maybe I'm the only one who does not have a hose connected to one of the three ports?

[Hornung418]

Is it possible I have it already but it's connected to a different port located somewhere else?

How about other owners? Maybe I'm the only one who does not have a hose connected to one of the three ports?
Snap a cell phone shot of the back of the manifold when you have time. That should clarify a lot of things for a lot of owners.

[Dave1027]

My engine is basically this pic but with all three ports capped.

http://www.bimmerforums.com/forum/attachment.php?attachmentid=525911&stc=1

[Hornung418]

My engine is basically this pic but with all three ports capped.

http://www.bimmerforums.com/forum/attachment.php?attachmentid=525911&stc=1
Can't see the picture.

[ryankokesh]

Me either.... :foottap

[wsmeyer]

18368

You can get back there without removing anything. I have three that are all capped, two about 1/8ID and one about 3/16ID. The larger of mine was cracked so I replaced it with a red cap you can see in the pic.

[LivesNearCostco]

Thanks, I will inspect them by feel sometime soon. I have removed the brake booster/DME shield a few times, mostly recently when I replaced my heater hoses and starter. Also removed cabin air filter assembly recently to replace VCG.

Hornung, I haven't yet inspected the back of my manifold but am pretty sure my SAP valve does NOT have a vacuum line attached. Other E46 threads have talked about this line but I just don't see it, and I still have stock exhaust manifolds. My SAP assembly has two electrical connections and my theory is the check valve is just a one way valve that lets the SAP push air into the exhaust manifold but doesn't let exhaust gasses escape and melt the SAP when the SAP is not pumping in air.

Or... maybe the valve is electrically activated?

Looking at the ECS Tuning catalog for E46 330 cars, it appears their SAP kit for cars up to 02/2003 includes vacuum lines and the SAP kit for cars from 03/2003 forward does not include vacuum lines.


Yep. I replaced my rubber caps by reaching around the back of the manifold. I did have to remove the shield around the brake booster to easily get my arm in there. You cannot see the ports. Go by feel only. To remove the plastic shield I also had to remove the airbox, intake boot and cabin filter assembly.

[Hornung418]

Hornung, I haven't yet inspected the back of my manifold but am pretty sure my SAP valve does NOT have a vacuum line attached. Other E46 threads have talked about this line but I just don't see it, and I still have stock exhaust manifolds. My SAP assembly has two electrical connections and my theory is the check valve is just a one way valve that lets the SAP push air into the exhaust manifold but doesn't let exhaust gasses escape and melt the SAP when the SAP is not pumping in air.

Or... maybe the valve is electrically activated?

Looking at the ECS Tuning catalog for E46 330 cars, it appears their SAP kit for cars up to 02/2003 includes vacuum lines and the SAP kit for cars from 03/2003 forward does not include vacuum lines.

There's a hard line that runs from the metal valve on the head to the back of the block. It's totally there if you have the SAP.

[Hornung418]

http://tapatalk.imageshack.com/v2/15/03/04/86d8a1a44c5dd28784a38f75056b5dd5.jpg

[LivesNearCostco]

OK I didn't look for a metal hard line or for the switch thing to be in the back near the manifold ports. I'll look for these next time I'm in there.

[Hornung418]

OK I didn't look for a metal hard line or for the switch thing to be in the back near the manifold ports. I'll look for these next time I'm in there.
It's possible that the line is bundled in with the O2 sensor wires that run along the VCG.