E39 1999 528i Rough Idle/Stall

[thedude2470]

Hello =]
I have had this problem for a little while now where after sitting at idle for a few seconds, the rpm's drop enough to make the idle very rough. Every so often, the rpm's will dip way down and the engine will almost stall. So far, I only had it stall once on me. Other than the idle, the car runs fine.
I recently had a problem with one of my cam positioning sensors, which threw an error code and tripped the light. I had that replaced thinking it was related to the idle issues, but it didnt help =[ The light has remained off though.
In reading some common problems here, I found that many people have issues with their MAF sensor. Should I try unplugging it? Do I do this while the car is running or off?
Also, I dont know if this is relevant, but with the cold weather here, the problem seems to be worse.
Thanks for the help.

-Kevin

[marti5]

Have the car running, unplug the MAF and see what happens, do you have any oil around the spark plugs?

[thedude2470]

Originally Posted by marti5

Have the car running, unplug the MAF and see what happens, do you have any oil around the spark plugs?

Thanks =]
I will try this at lunch, as well as check for oil around the spark plugs.

I just read something rather disheartening though, having to do with a "vanos problem" that is apparently a known issue with my model. Symptoms match exactly.

[marti5]

Yea , It maybe the Vanos, depends on mileage and service history it normally goes around 100K.....but it will probably only be the seals and not the unit....

[rajk9800]

those are all possible sources. the vanos should be checked last. is your car a cold weather car? (secondary air pump could be failing) how many miles? 80k-120k all top end gaskets should be replaced. (valve cover, intake manifold, throttle body) all vacuum hoses inspected &/or replaced!

bmw's rely on high oil pressure & a solid vacuum system. you can fix one rough idle and uncover another. it can be very trying at times but, easily done.

[thedude2470]

Originally Posted by marti5

Yea , It maybe the Vanos, depends on mileage and service history it normally goes around 100K.....but it will probably only be the seals and not the unit....

Ok, there isnt any oil around the spark plugs, and unplugging the MAF caused the engine to rev a tad, return to normal, but then continued again with the rough idle and almost stalling, so I dont think thats it.
The car has 164,000 miles on it. Bought it from my aunt a year and a half ago with no problems. Im not sure what she had done it to it, but she took very good care of it.

Should I start with what rajk9800 said by replacing gaskets, etc.?
Also, is it simple to diagnose whether or not its the vanos?
Thanks for the help, much appreciated.

[rajk9800]

since you know where the car came from i would ask her more info. or ask who did the work? if it was serviced at bmw dealer you can have them run the vin. if they did the work than records will be on hand, if it was another bmw dealer they will tell u who and call them.

if it was an indy or joe blow be careful. i have seen people put the car back together wrong or not reconnect everything. the funny thing about bmw's is that they can run on limited capacity & u would barely feel it.

if no oil in plugs than check the left side of valve cover gastket and back side.( looking at the car it will be on left side of valve cover) no oil leaks than good!

with your idle rough & changing, it sounds more like a vacuum leak. this could be anywhere. (intake manifold gasket, throttle body) u never answered about acold weather car?

cam sensor is only will affect one part of rpm rough idle. i have been thur all this already. there is a good start 5 out of 10 wrenches

[thedude2470]

Ops, sorry. I was a little confused by what you meant. Do you mean is the car winterized? or do i live in an area with cold weather?
If its the first, then no. The only thing I had done for winter was snow tires.
If its the second, yes, I live in Buffalo, NY.

[burt ragio]

The surge at idle is most likely caused by a leaky vacum hose. That would be the 1st place to look.

[ozarkmark]

If it isn't a vacuum issue, it could be a dirty ICV (idle control valve). I had a reputable import mechanic diagnose this and he simply pulled it out and cleaned it. No problems since then until I traded...

Check the vacuum thing out first though. Good luck.

[davido]

sounds like idle control valve had similar fault with 525 e34 pulled it out cleaned with carb cleaner cured problem though have not had similar problem with e39 523i i now own.this valve takes a signal i beleive from the ecu and does the same job as mixture control screw on old carb engines weakening and enriching fuel/air mixture to suit weather conditions like choke did on older cars, hope this helps also consider plugs mine runs far better after changing to bosch super 4s with better throttle response over standard 2 electrode plugs.

[davido]

Further to my other reply the other thing to consider is cleanlness of oil as dirty oil/blocked oilways can cause havoc with haudrilic cam followers as they do not lift correctly if starved of oil but to be honest i am 90% sure that it is throttle control valve as mentioned before as all your symptoms point to this,as i do my own servicing i always use engine flush first then a good quality semi synthetic oil on my car which is 98 model i beleive long life oil was only needed on 2000 and above engines this semi oil was recommended by bmw agent i did try mobil 1 fully synth but found cam followers very noisy down to viscosity i beleive.u,k bmw owner for last 10 years.

[BimmerE39]

Originally Posted by thedude2470

Ok, there isnt any oil around the spark plugs, and unplugging the MAF caused the engine to rev a tad, return to normal, but then continued again with the rough idle and almost stalling, so I dont think thats it.
The car has 164,000 miles on it. Bought it from my aunt a year and a half ago with no problems. Im not sure what she had done it to it, but she took very good care of it.

Should I start with what rajk9800 said by replacing gaskets, etc.?
Also, is it simple to diagnose whether or not its the vanos?
Thanks for the help, much appreciated.

It's more than likely your VANOS unit. I have a 2000 and the rubber seals inside the unit are notorious for failing over time because of the heat and chemical nature of the environment. On particularly cold days the engine would idle oddly until it reached operating temperature.

There is an easy test to see if it's your VANOS unit though...


If you unplug the sensor and the idle smooths out you can almost be guaranteed it's your VANOS.

[davido]

hi hope you all had a good xmas further to above there is a excellent item on idle control valve with photos on bimmerforums.com tells you where to find and how to clean the only thing i disagree with is use of wd 40 as this can leave a residue use only carb cleaner wynnes or similar or carbon tetroflouride based contact cleaner,lublicate with brake fluid hope this helps.david uk.

[Poolman]

Classic Vanos symptem--read below for the cure--your car will love you for it
Beisan Systems - Procedures - Double Vanos Procedure