idle is REALLY annoying ! any solution ?

[J-Michel DIY]

Hello guys,
Now I got this erratic idle between 600-700 rpm with warm engine and below 1000rpm (cold engine). Above that the engine has all the power and not misfiring at all (I changed one ignition coil a couple of months ago which solved the problem of misfiring below 3000 rpm).

My bimmer is a european 320i with an M50 6cyl engine. Basically same as a 325i but with 2.0 liters and I dont have the OBD functions...so I cant read codes !

I removed the intake manifold last weekend and sealed everything back with silicone compound and checked all hoses for leaks. I cleaned the ICV with DW-40. I put everything back but there was no improvement at all ! Then I bought a new ICV valve (200$) at the dealer here in Germany...and guess what ?...NO IMPROVEMENT ! I am getting a bit irritated now and I'd like to get your opinion/experience on this matter. I read quite a lot of postings on internet but I am not sure what to think about.

I also got my end stock muffler which is loud and exhibiting strong pulsations but is not perforated at all. It seems the inside is a bit old. I thought that could eventually cause some disturbances in the exhaust line flow somehow that the DME can't really compensate (that explanation sounds weird though).

I am thinking of changing this 02 sensor, but not sure yet. The engine is annoyingly shaking and that makes me think of bad spark plugs, but they are new and I am sure these are the right ones.

This idle shaking is not so strong but you can feel it when you are seating in the car...ANNOYING !

Any help will be very much appreciated. THX

[J-Michel DIY]

To keep you posted:
I Brought the car today to the BMW dealer to check the diagnosis errors (for free !!!) ...and finally the dealer found no errors, but it still shakes at idle...weird.

[Jeron]

Could it be a physical problem such as bad motor mount or missing fan blade etc. throwing the balance off?

Did you make any changes before the onset that may be related?

[J-Michel DIY]

Hello Jeron,

Motor mounts and fan blades are good so far. It really feels like one piston is not properly firing at idle, like a bad spark plug, but they are brand new and it was the same behaviour with the old ones. There is no lack of power during acceleration at all either.

One clue might be that at cold start the engine does not rev very high at around 800rpm and when warm at 600rpm. Could it be related with some sort of temperature sensor malfunction not detected by the diagnosis ? but I saw there are several temperature sensors: 1 in the air filter, 1 in the block near the front of the engine (coolant sensor). I also saw one sensor plugged into the intake manifold at the right side of the throttle body (not sure what kinda sensor is that ?)

[Dave at Pelican Parts]

Did you use a silicone sealant that was specifically labeled "O2 sensor-safe"? I know that silicone can kill off an O2 sensor, but there are RTV sealants that won't.

No other good ideas for you, unfortunately.

Can you tell if the mixture is OK at cold idle? Check the plug colors, etc.

--DD

[Jeff]

J-Michel, Have you looked under the hood in the dark with the motor running? You should be able to see if you have a crack in the ignition system. You will see sparks escaping. (If your engine is like mine you will need to remove the cover over the spark plugs).

Also have you checked all your vaccuum lines.

[J-Michel DIY]

Dave:
the silicone is not mentioned sensor safe but the problem occured before I put this silicone stuff. And at the dealer they also didn't find any o2 sensor error.

CUL8R:
I definitely checked all vacuum lines more than twice.
Sounds interesting what u say about crack in the ignition. I might give it a try. One more thing, when I changed my spark plugs, the hole in which the plugs sit was kind of filled with oil. I found out that the head cover gasket is leaking a little but not so much. I am thinking of replacing this head cover gasket cause it could act as a bad vacuum problem.

Thanks for your feedback guys.

[J-Michel DIY]

Dave:

About the spark plug colors they seem to be fine for me. A little white. seems normal to me.

[Dave at Pelican Parts]

White means a bit lean, which might explain the "hunting" idle. But would not explain why the idle is so low when the engine is cold. I don't remember Mom's E36 having such a low idle, cold or warm! If cleaning and then replacing the ICV didn't do anything, perhaps the signal going there is bad? I might guess that the coolant temp sensor is not reacting the way it should... But it is only a guess!! Unfortunately, I don't know how to test that sensor.

If the shaking is really bad inside the car, I would take yet another look at the motor mounts, too.

--DD

[J-Michel DIY]

If there is a faulty temperature sensor signal and the DME is reading "too high temp" the engine will start retard the ignition. At idle my engine behaves as if the ignition was actually retarded and that might give this lumpy ride.

I bought the 2 coolant temperature sensors. I will install them tomorrow. I also ordered the O2 sensor for tomorrow. Let's see what it comes up !

Next step I guess is air temperature sensor...

I also bought the alternator belt which is starting to show cracks. I read that if the belt is slipping and the alternator is not rotating fast enough and not giving enough power, that could influence the ignition at idle. (it should trigger a charging light on the dash which it doesn't now...but the belt is old and needs to be replaced anyways).

[Jeff]

J-Michel, Let us know which one was the fix.