BMW won't help me so it's DIY time

[Paraklas]

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.

What's the first thing to check?

I've replaced the engine gaskets, idle valve/ relay, fuel pump (was defective), fuel lines, fuel filter, oil filter, air filter (K&N), spark plugs.

I'm thinking of cleaning the air flow sensor is that a good idea as one step further?

[and0pand0]

Quick post...

IF YOU HAVEN'T DONE SO ALREADY:

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?

This may help: http://www.pelicanparts.com/BMW/tech...leshooting.htm

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.

Good luck!

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.

[Paraklas]

I can see some oil buildup around the oil re-circulation hose, I'll replace the hose. I'll also replace all the vacuum hoses as well.

Valve cover gasket checked and it's ok. The fact is that I do not always have bad idle, only 99% of all times.

How can you tell from spark plugs if you run rich or lean?

What's the CEL ?

Thanks!

p.s. I've read somewhere a post that someone removed the air flow sensor and cleaned it with carbuerator cleaner, let it dry, and then re-installed it but I can't find the info anywhere..

[Kowalski]

the color of the plug tells you. however i forget the colors... grey is healthy i believe... brown is lean, and black is rich. i believe thats how it goes...

[Paraklas]

Just noticed that car runs much better (bad idle is less noticeable) when I use 100 octane fuel instead of 95 octane...

I hate this kind of problems that the source could be a load of parts

[Starmavin]

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.

[Paraklas]

Intake boot is clear from cracks (not a long ago that was replaced). I will check the rest in 3 weeks when I get back home again. (Glad the list of to-check-things is growing).

In addition to these, car takes about a second to go from idle to more rpm's when I press the gas pedal, like it's chocking or something!

[luckycat]

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.

Thats the Cats philosophy!

Good Luck!

[Paraklas]

At last, bad idle solved!!! A good cleaning of carbon buildups and adjustment of fuel.. Seems the car was running pretty rich..