Re: rough idle...

Subject:

Comments:
: : Thanks for the input, Walt! Since I posted last night, I have been tinkering (strike that, obsessing) with the problem....I am leaning towards a vacuum leak problem. Trying to match the Haynes manual up with the actual pieces of the emissions system is a bit of a trick. As best as I can tell, I have 3 vacuum lines coming off my throttle body. One goes to the vacuum advance on the distributer (the temp switch on the thermostat housing has been bypassed), one goes to the charcoal canister, and a large one splits. One branch goes through the additional air valve to the cold start injector and the other branch goes through a solenoid between the throttle body and intake manifold (vacuum limiter?) I know I have a leak around the line to the charcoal canister....The "barbed" fitting that the rubber line fits over has been boogered with pliers, and I was able to remove it with my fingers (Is that supposed to be press fit in? I didn't see threads and it does not look sheared off..). I must have other leaks or problems, because when I plugged the hole in the throttle body, there was no improvement. : : When I first start it cold, it runs smooth (little to no missing). As the temp switch makes, the idle drops back and it misses almost to the point of stalling (4-500 rpm when stopped in gear). It seems to idle at about 800 when it is hot, but it still misses. I tried Peter's tip on pumping the brake pedal, and the rpm would drop off more when I did that. : : Does anyone know the symptoms of a failure in any of the emissions components (the solenoid or aux air valve). I have a feeling that the previous owner/mechanic has messed with the emissions system, so I would also appreciate it if anyone can confirm that I am not necessarily missing too many components.... : : I figure I will try replacing a bunch of the rubber tubing, and then maybe resort to a tune-up by a mechanic with an O2 analyzer.... : : Any other suggestions? : : First of all I would try to seal all the vacuum leaks. Use hose clamps if necessary (on hoses that normally don't have them) to make sure all the hoses are sealed. : Unfortunately I don't remember the vacuum hose routing on a 528i (I didn't drive the car to work) but it is important that the hoses come off the correct port on the throttle bodies so that the vacuum timing (as the throttle opens) is correct. : It sounds like your car is possibly running a little lean at idle (brake pumping test). This can be caused by vacuum leaks or misadjusted mixture. One thing to consider is that if you have one cylinder misfiring sometimes (due to ign or intake problems) this will give the 02 sensor a rich indication. Then the computer will lean out all 6 cylinders to get an average 14.7:1 reading from the O2 sensor. So what you get is 5 cyl running too lean and 1 cyl running slightly rich (and or missfiring). The result is that the engine runs like crap. The car may run fine when cold because the 02 sensor hasn't heated up yet and the car is still running open loop so you get 5 cyl running perfect and 1 cyl unhappy but the result may be ok running when cold. : Regarding the aux air (slide) valve you can check it by putting it in the freezer. After it has cooled down you can look through it and should see a half moon opening. When the engine is warm the valve should be closed. : In general you just need to systematically work through all the possibilies. If the car is almost stalling you can temporaily increase the idle speed to help out a little. : Walt Barie

Optional Link URL:
Link Title:
Optional Image URL: