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Z3 m44 rough idle

6060 Views 4 Replies 5 Participants Last post by  vintage42
I have a 96 z3 1.9 m44.

The car has had a rough idle since I bought it; Only 75,000 miles on it.

I changed:
Cam position sensor
Front o2 sensor
Spark plugs
Coil on plug conversion
Pcv valve
New intake gaskets
Replaced vacuum lines going to injectors
Fuel filter
Coolant temp sensor
Valve cover gasket (oil on plugs)

None of this fixed the problem, although the idle is 100% better now.

It still idles rough and began hesitating while cold. I'm considering a new maf, crank position sensor, throttle position sensor and possibly idle control valve.
I've been advised a fuel pressure regulator could be the cause also.

I pulled the lower intake apart the other day to see what's going on. I found black gunk on the ends of the injectors as well as all inside of the intake where the injectors go. It was also on the intake valves, this came off easily with carb cleaner and degreaser. The car ran horribly until I revved it for a minute, I guess it had to work out the cleaner.

Anyone have any insight on this?

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CRANK CASE VENT VALVE Part # 11157501567 $61.05
Sounds like a vacuum leak, the plunger in the value will break letting the O-ring seal move and create a vacuum leak. Engine will idle until warm and settle around 800 RPM's than start to stumble and run rough, a little gas and it gets better than repeats. Break the seal on the oil fill cap and see what a crankcase vacuum does, it's not good. Anyway, that was my problem in same engine, hope it helps..
Also might want to try a good fuel system cleaner. I add a good fuel system cleaner to my tank before I fill up every time. Keeps fuel system injectors valves everything good and clean no carbon build up which these cars are prone to do. I also run premium gas only.
Hey KillerSeven,

I don't know if you ever got an answer to this or figured it out. I'm guessing you might have sold the vehicle by now but on my 1998 318ti with the M44 engine I went through a year of replacing everything on it thinkable and still had rough idle. Now before anyone says this was probably not that way to go, I picked up the said vehicle for $500 knowing full well it needed a complete overhaul. I've put thousands into it because I love it. I eventually swapped the motor out for an m3 and put the m44 into another motorless 318ti. In the swap out process I decided to tear apart the m44. The lower end was fine but the head needed a lot of work. I ended up replacing the guides and getting the valves back to factory spec. In the second ti this motor went into with all of the parts from the first, the idle issues were gone finally :). I've seen it in other places that the valves not closing correctly due to worn out or faulty guides is a cause of idle issues in the M44. I think BMW even had a service bulletin out for it at one point. It's way later for a response and digging up this thread but I figured I'd send that your way.
I have not seen KillerSeven here for a long time, maybe a year. Bad valves are a good reason for rough idle, but it takes a very long time for the hydraulic self adjusting M44 valves to go bad, so we rarely ever hear of it.
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