rough idle and surging on very cold mornings
Hi all. I have a 93 525i m50. When the weather started getting very cold I have a very rough idle and surging and a cel indicating an oxygen sensor in the morning. Car seems like its going to stall sometimes at stoplights. When the car warms up the cel dissapears and all is normal. I replaced the o2 sensor with a new bosch unit 7 months ago. I found some splits in the hose connections on the intake boot and replaced with a new one. I also replaced the throttle body gasket because it was easy and cheap. fuel pump is new. I am suspecting a vacuum leak. The oil cap is new as well as the valve cover gasket and asscociated plug gaskets. I am going to spray carb cleaner around the intake gaskets and check for leaks. I already purchased the gaskets. What could it be?
Re: rough idle and surging on very cold mornings
after you rule out possible vacuum leaks, I would check the idle valve. You can actually tap on the valve with a hammer or extension. It could be binding when its cold
Suggest you clean idle control valve
This is a type symtom of a sticking ICV. If it had not been cleaned before, you will need to remove it to clean. Use some throttle body cleaner to spray into the valve several times. I use pipe cleaners or Q tips to wipe out the gunk. Continue to spray until rotary valve will move back & forth when spun with your hand. Biggest issue is getting to it on the M50 engine. If I remember correctly, it's located below the throttle body/intake manifold & is difficult to see & get to. Attached is a link for the E36 but it's basically the same engine.