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Discussion Starter · #1 ·
I own a 2003 325i with and M54 engine

As i check the codes online I find that it says Bank 1 sensor 1 mixture too lean and Back 2 Sensor 1 mixture too lean.

Which people automatically said I had an Air leak, Which ended up being true.
So I figured changing the CCV would be a start since it was old anyways and after I was done my car ended up being worse then how it was. It would start and misfire and also the idle was horrible so It took me 2 weeks before i found the problem. For people who have similar symptoms please take my advice before you buy anything.

Changed CCV and hoses which later caused misfire and horrible Idle.

So I did the following
Intake manifold gasket
Throttle Body Gasket
Disa Gasket
ICV grommet (Rubber Gasket on ICV to intake)
New Intake Boots(Upper and Lower)
All new Vacuum Hoses the ones on the F tube and the ones in back of manifold by firewall.

And still no fix, So i did the smoke test with a cigar and a vacuum hose.
Tested the F tube on the upper boot and found no leaks.
Tested the CCV and found one leak coming from the hoses which wasnt completely connected. (Fixed Misfires)

Now down to the horrible Idle

Tested the oil dipstick tube.........Found another leak which ended up being the O ring at the bottom of the Dipstick tube. ( Fixed the Bad Idle)

Still getting Lean codes though so I figured all pipes are good except one and that was the one that goes from the F tube to the Fuel Filter and there was another leak there aswell( Fixed the Lean Codes and boom problems gone)

So if you guys have bad idle or misfire check the
Intake Boots (Upper and Lower)
The Mass Air Flow sensor has an O-ring that goes from the MAF to the Air filter Box
Vacuum Hoses
-Back of intake manifold has 2 of them, 1 goes to the front left of the engine, and the other like to inches away around the same spot.
-F tube has 2 one that 1 goes to the Intake and the other to the Fuel Filter
-CCV has 4 hoses, 1 goes to the Valve Cover, 2nd goes to the top of intake manifold, 3rd goes to the Hose that goes to the top of intake, And 4th goes to Oil Dipstick tube.

To do the DIY Smoke Test buy a cigar, any tube that will fit in either the Oil Dipstick tube or one of the CCV hoses try the one that goes to the Valve Cover and the one that goes to the Intake Manifold, and also the F tube thats how i checked for the boots to see if they were leaking but for the hose that goes to the Fuel filter u will have to remove the cover under drivers seat and see for yourself because i dont think U will be able to see smoke from there, Also the ones behind the Intake ,just feel around because I dont believe smoke reaches that point so i used a miror and my flashlight and found a old cracked hose just by feeling the hose you could tell if it needs to be changed.

Hopes this helps.
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