330xi rough idle/misfire codes

My 03 330xi just developed a rough idle the other day. It fluctuates between 550-750 rpms. However as soon as throttle is applied, all is well.

Had it scanned, and 5 codes showed up. "Misfire upon startup" for cylinders 1, 2, and 4, and 2 seperate "random misfire" codes.

It is still driveable, just sounds as if it had a cam at idle.

Car has about 118,000 miles, mostly stock (Intake/Exhaust), 6 speed. Recently replaced the exhaust cam sensor, as it was malfunctioning. Haven't had any issues since, I don't think it's related, but thought I'd mention it.

Is there any common fixes?
IAC?
MAF?
Vacuum lines?
Any other ideas?

Thanks in advance!

Can you post up the actual codes? When's the last time you changed the plugs? How about the coils? Any issues with the valve cover gasket leaking? Do you have an auto or a manual?

I can go back and re-scan it later, I didn't write down the codes.
I just purchased the car about 3 months ago, I believe he said the plugs/wires were done within the last year or two. Unsure on the coils.
I haven't noticed any issues with the valve cover leaking, I'll take a closer look tonight.
Car is a 6 speed manual.

Read the guide by jfoj (just search for any of his posts - its in his signature)...

Well the commong fixes are as you listed them.

-IAC is clogged/dirty, but this shouldn't be a sudden onset thing. Can't hurt to clean it out. I still need to do mine...
- MAF, clean it up. I do this every oil change as common practice. Also forces me to check the condition of the air filter.
- Vacuum lines should have thrown a code of some sort.
- Check intake track for holes/tears/cracks/whatever.

Just went and scanned it again, new code this time. P1345, "Misfire Cyl 2 with fuel cut off". Also noticed a new symptom, when at a stop, if I blip the throttle lightly (to maybe 2k) it tries to "catch itself" before returning to idle. In other words it attempts to steady itself around 1100-1300rpms, then slowly drops to about 500-700 where it idles erradically again.

Could this be a DISA issue? As I said, anything above idle seems absolutely normal. As I understand it, DISA issues typically cause rough idle as well as sluggish acceleration. Correct me if I'm wrong..

I'll take a look at that stuff later on, I have a limited amount of tools/space at my new place. :/

^disa and intake boots are easy to check.

The easiest way to diagnose a bad DISA is the jar of marbles sound it makes when it breaks.

Does it make that sound while running? Or after removing by shaking it?

Thinking back, I do remember maybe 2-3 times I had a similar issue that lasted for maybe 15 seconds, but as soon as I either shut the car off, or left the stop sign/light, the problem went away.. Maybe those were early warning signs for something?

Also, I first noticed this yesterday after a "moderate acceleration" from a stop light. I got on it a little bit, and then shortly after pulled into my apt building, and noticed immediately the erratic idle. Could the DISA valve have gotten stuck while I was under somewhat heavy acceleration, and just hasn't released yet?

Forgive me, I'm still trying to fully understand the DISA valve's function.

Originally Posted by Silversixspeed

Does it make that sound while running? Or after removing by shaking it?

While running. You can remove it easily though and check the flap operation. Should be nice and tight, if it's broken it'll just spin freely.

Originally Posted by Silversixspeed

Thinking back, I do remember maybe 2-3 times I had a similar issue that lasted for maybe 15 seconds, but as soon as I either shut the car off, or left the stop sign/light, the problem went away.. Maybe those were early warning signs for something?

Also, I first noticed this yesterday after a "moderate acceleration" from a stop light. I got on it a little bit, and then shortly after pulled into my apt building, and noticed immediately the erratic idle. Could the DISA valve have gotten stuck while I was under somewhat heavy acceleration, and just hasn't released yet?

Forgive me, I'm still trying to fully understand the DISA valve's function.

This doesn't sound like the DISA at all. The DISA valve controls the two different intake runners in your intake manifold. One is dedicated to low end torque and the other to higher end horse power. I ran my car with a broken DISA for 3 months and didn't notice too much improvement with a new one.

I would check out your ICV and the coil/plug for cylinder two.

I'll check all of that, but if it were a plug/coil for cyl 2, I'd imagine I wouldn't have had all of those initial codes.. I sent a message on another forum to the previous owner, hopefully he can recall what maintenance he's done recently.

Did you get records of all work done? If not, then huge mistake.

I think I have a pile of receipts, I just can't seem to find them anywhere.

Just scanned the car again, these codes showed up this time:

P1352 "Misfire during start cylinder 6"
P1348 "Misfire during start cylinder 4"
P0300 "Random cylinder misfire detected" The Autozone printout (don't hate me guys, it's right next to my work) says Explanation is "Lean Air/Fuel Ratio".

I've also noticed that, while coming to a stop, with the clutch in, the "MPG gauge" rises and hovers between 15-20mpg, with no throttle applied for about 4-5 seconds, then goes to 50+ (normal for idle). I'm assuming this is essentially a vacuum gauge? If so, is this telling me anything? I don't remember it doing that previously..

Check your intake for leaks. That's the most consistent source of a lean condition. Leaks can be had from intake track itself in the form of cracks and tears as well as from the DISA o-ring and any vacuum lines that are torn. I don't believe the vacuum lines are the problem for you though so check the intake and clean your MAF and IAC.

Is that ICV easy to get at with the DISA valve removed?

^ Nope, you have to remove the entire intake runner to get to it. Also, when you do get to it the hose clamp holding the hose to the valve will be installed upside down and is a PITA to get out. Key is small hands and a small screwdriver or nut driver.

You should be removing the whole thing to check for cracks/tears anyway. Be careful with the F tube, it tends to break easier than you'd think.

^I've seen the ICV removed in under 10 minutes with a flexible ratcheting nut driver.

Originally Posted by Kubica

^I've seen the ICV removed in under 10 minutes with a flexible ratcheting nut driver.

I don't have one of these... OP if you don't have one either it'll be a PITA.