3-Series (E21, E30)Chat relating to the BMW 3-Series from 1975-1983 and 1984-1991 line. Specific models: BMW 315, BMW 316, BMW 318, BMW 318i, BMW 320/4, BMW 320i, BMW 320/6, BMW 323i, BMW 320i. E30 Family models include: BMW 325e, BMW 325i, BMW 325is, BMW 325ix.
Car has reached 200000km without any probs except the so much discussed eratic idle problem. I want to fix that. BMW dealership here don't want to spend their precious time looking an old M40 engine to fix this problem (as it may have multiple sources) so I thought of starting doing things myself.
Replace vacuum hoses. Check valve cover gasket. Also check for oil leaks and replace seals/gaskets that are leaking (including rear main seal). Check your spark plugs to see if you're running rich/lean (this will help you steer in the right direction). Rich means fuel issues. Lean means vacuum issues. Check that the fuel pressure regulator operates properly. Do you have a CEL on?
There's plenty of idle problems with these cars. Search these forums and you'll find a lot of posts about it. Mine doesn't idle right, but I don't have the money to fix it right now. Also, it's an M42, so it's harder to find rock-solid info on troubleshooting stuff.
Also, I don't think you can clean the AFM without damaging it... I could be very wrong, however, since I've never looked into it.
Check the intake boot for cracks and tears. This will cause the air flow meter to read less air than what is being sucked in, the o2 sensor read a lean condition and riches up the fuel mix, IE rough idle. Also check the throttle position switch. On the car, pull the intake boot and unplug the connector you'll see 3 terminals test the left and middle for continuity when closed, the right and middle when fully open. If either or doesn't check out it may need replacing or adjusting.
I have sucessfully cleaned my MAS with carb cleaner several times without damage. Just two 10mm nuts secure it. (and the intake hose) If you in doubt about it, remove it and check that the action is smooth without binding. Check to see that it snaps all the way home. Clean the connector with contact cleaner.
A good way to check for air leaks is to spray carb cleaner around all the hoses and fittings.
If the idle increases, voila! you have found the leak!
Make sure that the idle switch located beneath the intake manifold is working properly. Move the throttle body and listen for a click, check the connecter with an ohlmeter if possible.
There problems are sometimes tough to figure out, but just look it as a challange. When you fix it, you will have learned a lot about your car.
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