Post VANOS Rebuild Issues: Rough Idle + Popping Sound

Car: 2004 ZHP(M54B30 Double Vanos)

I'm having an issue with my car after installing the Beisan systems seals and anti-rattle kit. The actual re-building of the VANOS systems was a breeze especially with the directions provided by Rajaje . No complaints here.

I did however break a VANOS bolt and it fell into the exhaust spline shaft. I ordered the German Auto Solutions double VANOS cam timing tool kit and removed the broken bolt from the spline shaft. I had to re-time the motor and got everything timed correctly. I verified by manually turning the crank clockwise twice and:
-Made sure the cam lock blocks sat evenly with the head
-Verified the dots on the back of the cams were facing upwards
-Verified the harmonic balancer was showing TDC with both cam lobes facing each other
-Used locking pin to lock TDC on bellhousing


I made sure everything was put back together properly using all new gaskets, washers, seals, etc. I installed new spark plugs and verified all of the wiring and connections. When starting, the idle is very rough. It seems like it is misfiring on many cylinders. After the engine runs for a few minutes a very loud "popping sound" comes from the intake manifold area. I immediately turned the car off and haven't started it since. The sound is identical to this:






2 weeks ago I completely overhauled the CCV system with all new hoses and the valve. I cleaned the throttle body and ICV. The car ran flawlessly afterward.

I'm thinking I've missed a sensor or bumped the crank position sensor loose after removing the locking pin from the crankshaft on the bell housing.

If you can provide any feedback at all, I'd appreciate it greatly. I'm sorry if I've not made myself clear or the post is somewhat "wacky". It's 1:45am and I've been at it for 14 hours....


Thanks Fanatics, I hope you can help me as much as I've been able to help others. I love this place.

I did however break a VANOS bolt and it fell into the exhaust spline shaft.

Can you elaborate on this? I'm not understand which bolt you broke that required re-timing of the VANOS.

Is that video of someone else's car that sounds like yours, or is that of your car?

I'm hoping the reason it sounds like something metal bouncing around inside your engine is due to cell phone audio quality. Other than metal parts dancing inside your engine, I would guess back firing through an intake valve. This could be caused by a bent intake valve or a grossly mistimed intake cam.

Originally Posted by MotorMan

Can you elaborate on this? I'm not understand which bolt you broke that required re-timing of the VANOS.

Is that video of someone else's car that sounds like yours, or is that of your car?

I'm hoping the reason it sounds like something metal bouncing around inside your engine is due to cell phone audio quality. Other than metal parts dancing inside your engine, I would guess back firing through an intake valve. This could be caused by a bent intake valve or a grossly mistimed intake cam.

I broke the bolt that connects the exhaust helix cup to the exhaust portion of the VANOS. It actually fell into the helix cup and required me to remove the intake and exhaust chain gears to remove(so I though, I later found out I could have removed the helix cup without doing so).

The video is not my car. It is very similar however. It is not a metallic sound, it sounds more like a plastic popping sound. Can you elaborate more on the mistimed intake cam?

I broke the bolt that connects the exhaust helix cup to the exhaust portion of the VANOS. It actually fell into the helix cup and required me to remove the intake and exhaust chain gears to remove(so I though, I later found out I could have removed the helix cup without doing so).

OK, that makes sense. I couldn't think or a reason that you would have to remove the cam gears to retreave a helix cup bolt.

Can you elaborate more on the mistimed intake cam?

I may have to recant that statement. Upon thinking more about it, I can't think of an intake cam timing scenario that would allow the engine to fire with the intake valves still slightly open and still be able to run. I need to think a little more before I start typing.

Unfortunately I keep coming back to a bent intake valve. Did you ever try to rotate the crank while the cam gears were removed? Is the car setting any codes? There are lots of things that can cause rough idle, but the backfire through the intake manifold (if that is what it is) scares me.

No problem at all, I really appreciate your input.

Could you tell me some for certain signs of bent intake valves? I pulled P0303.

I don't remember if I turned the crankshaft while the gears were removed, it's possible.

Could you tell me some for certain signs of bent intake valves?

If you have a bent intake valve, that cylinder usually won't build enough compression to fire, but every once in a while the mixture will ignite and the resulting pressure will flow backward through the slightly open intake valve and into the intake manifold, hence the popping noise.

You can check for a bent valve with either a compression or leak down test. A compression test will verify the low compression and pin point the cylinder. A leak down test will do all that, plus verify whether the problem is an intake valve, exhaust valve or piston ring sealing. In your case just a compression test would probably be enough since we can assume what the source of the problem is based on the other evidence.

I'll get my hands on a compression testing set and give it a shot once everything is put back together. Is there a certain procedure I should follow for a compression test on the M54?

Is there a certain procedure I should follow for a compression test on the M54?

Opinions vary.

I recommend that all spark plugs are removed, have another person crank the engine over (fully charged battery) with the throttle held wide open while you watch the gauge. Have them stop cranking once the gauge reading stops rising.

It's not a bad idea to pull the fuel injector connectors or disable the fuel injection in some other way. It's also best to perform the test on a warm engine, although I would understand your hesitation on running the engine anymore than what is necessary until the problem is diagnosed.

Good luck.

Much appreciated. I'll keep you posted.