andymax

I had this posted on Bimmerfest too, but didnt have much luck finding a solution. Wondered if my luck would change here on 5Series.net....

Here's my situation:

1. I have a slightly rough cold-start idle which smooths out when warm
2. Whether warm or cold engine, if I get on the gas even moderately I get what feels like a fairly significant engine misfire...no pattern to it, or predictable condition ...just random misfire. Feels like a random series of hiccups, so to speak, when accelerating. When I back off, car runs fine.
3. If I drive moderately and/or light on the throttle, no issue.
4. NO CODES - checked multiple times with full version of BMWHAT
5. NO SES or any dash lights, exclamation points, bongs, etc.
6. Injectors replaced a while ago with the most current version (version 12 IIRC??)
7. Nothing else seems affected.
8. New plugs 10K miles ago.
9. ALWAYS run 93 octane
10. This issue came on fairly suddenly
11. No change in fuel mileage.

When searching this issue I find similar conditions, but always with a fault code or SES light, or some other tell-tale symptom that I'm not getting.

Anybody have any ideas?

-Walnut blasting comes to mind, but not sure that carbon buildup explains the issue.
-Ignition coil also comes to mind, but wouldn't that throw a code?

Any ideas would be much appreciated...

twh

I'll take a shot. It could be the intake manifold DISA valve. They are little flaps that exist inside the intake manifold that directs air one way or another.

Check out this explanation: BMW - The Magic DISA Valve - Atlantic Motorcar

A broken flap could cause your symptoms and there would be no codes.

Depending on your engine, you have one or more in the manifold. My 2006 530xi has two of them.

Here is a YouTube video:

cmyachtie

Check for codes with INPA, JIC it picks up,what BMWHAT doesn't .
Is this with 8 or 6 cyl engine?

InsipidMonkey

There were some good answers on the Bimmerfest thread already, #1 being walnut blasting. Not sure why you're choosing to ignore them. The N54 is notorious for carbon buildup on the intake valves, and if you've never had it done in 187k you're way overdue.

Read up on walnut blasting here or on Bimmerfest (especially the before/after pictures). It makes a huge difference.

andymax

I'm not ignoring anything! The point is that there was no consensus, so I didn't see any harm, and in fact I think it's smart to ask more people that may have similar experiences. In reality, the responses on Bimmerfest came in equally with Vanos and intake cleaning, and from only 4 individuals, yourself included. Certainly I'm pointed in a couple directions, but neither absolutely answers all my issues, so asking for more input seems like a fair thing to do.

Regarding walnut blasting, I'm well aware of the process, etc. In fact, if you read all the posts I clearly state that the walnut blasting may be the next step. However, my business partner has the exact same car, had the walnut blasting done at 80K miles and afterward said that my car ran just as well or better (I had about 135K miles at that time, and never had it done), so it's not an absolute fix. Yes, I'll buy the argument that it's good sense to have it done as preventative maintenance, but at the moment I need to be certain that I'm addressing the issue at hand.

Additionally, I am making the assumption that the intake buildup is something that occurs over time and would manifest itself in an every-worsening symptom. As I stated in the OP, this problem came on pretty suddenly, which initially indicates to me some sort of component failure. Lastly, I'm not the type to just drop cash unless I know what the problem is.

Thank you again for taking the time to help me out.

andymax

It's the Twin-turbo Six (535i N54 engine). You bring up a good point...I guess I can't be certain that Carly-BMWhat app will pick out every code, however I've never heard of anyone complaining about that either. Hmmm...

andymax

Thanks for the idea. Seems the DISA valve is specific to BMW's up to, but not after 2007. Mine is a 2008.

InsipidMonkey

I bought my 2008 535xiT at about 68k miles. Around 82k, I suddenly began experiencing the symptoms you describe: rough cold starts, "stumbling" like misfire at moderate throttle, and no codes. Luckily, the dealership covered the walnut blasting under "goodwill", and replaced plugs at the same time under the extended maintenance plan. Thus the problem can manifest itself suddenly, even though it likely built up over a considerable amount of time. If you look at the pictures of carbon buildup on the intake valves, it is pretty crazy how much can build up and how restricted they can become.

Do you have any mods that may lessen the carbon buildup? OCC or meth injection or the like? If it's really been 185k that's great. If/when you do the walnut blasting ask the tech to take a few pictures of the valves and post them here.

andymax

I will absolutely ask for pictures if I go the Walnut route...thats a great idea. I heard a fairly convincing story about a fuel system induction cleaning service, which to me sounds like an amped up seafoam treatment, but injected via the air intake so it passes around and through the intake valves, which is where the gunk problem lies. I may post that separately to get some feedback if anyone has tried that method. Know anything about that?

seanjordan20

Me personally I would not troubleshoot off of just the BMWhat app. If you want to absolutely see what your problem is and not just throw parts at it hook a laptop to the car with INPA and see what error messages you are getting. Even though a code is not thrown everything is logged. I am pretty sure you will find your answer. If you can not give specific codes everyone will just tell you there experiences/thoughts and give you advice on what they would do next. Those suggestions as I read your replies are not good enough for you to go through troubleshooting steps and preform some of the suggested fixes. Honestly, without a code to go off of your problem can be a number of things and could be fixed a number of ways.

If you want to make sure you are doing the right fix the first time then you will have to be reactive instead of proactive ( wait for a code). It is just the way BMWs are. To be proactive you have to have the necessary tools to read the warnings or messages on the modules or simply take it to the dealership and let them figure it out.