Really Odd Issues...Vacuum Leaks?

[bmwman91]

This has been getting progressively worse.  The car still drives fine, but I am becoming more and more worried.  Here are the symptoms summarized as plainly as possible.

- When the motor is still cold, I get lame mileage and a CEL when cruising at a constant speed for ~10 seconds.  If I let off the gas completely, or floor it the light goes away.  When cruising it comes back after ~10 seconds.  However, if I floor it and revv it to ~4000RPM in 3rd gear once or twice, my mileage will be back to normal when cruising and the CEL won't return.  This started maybe 2 months ago.

- When I cold-started this morning, it was idling around 1100RPM and had a CEL on.  The idle speed slowly dropped to about normal, but the motor was running terribly and misfiring.  It seemed to rev fine otherwise, and as soon as I backed out of the driveway and drove 20ft, the CEL went away and it idled fine.  However, I still experienced issue #1.

- This is very odd.  If I am fully warmed up and floor it, there is no problem.  However, if I revv it over 4500RPM I get a CEL as soon as I let OFF the throttle (no CEL when floored).  If I shift and give it gas again the CEL usually goes away as soon as I press the gas pedal.

- Sometimes, during hard driving, the CEL stays on and my WBO2 diagnostic light flashes the code for an overheated EGO sensor.

- The only code stored in the ECU is 1222, for a bad O2 sensor.

So, this means one of 2 things in my mind.  I either have a bad EGO sensor, or there is a vacuum leak somewhere.  Seeing as how my EGO sensor is less than a year old, and the WB ones are supposed to last quite a while, I am betting on a vacuum leak.  This would lead to lean-running, which causes the motor to "run hot" raising the exhaust gas temperature, and thus could be overheating my EGO sensor.  It would then be putting out a signal contrary to what the ECU wants to see, depending on what it does when overheated.  I have heard of many cases where a vacuum leak caused 1222.

Any input here?  All the easy to get at stuff looks just fine.  Are there any places the M42 commonly leaks (probably a big leak) that are not immediately obvious?  Thanks!

[haledj]

I would check your O2 sensor relay, and your coils first.  Then I would get a smoke machine and find your vacuum leak.

Your o2 sensor could be worn out, widebands last less mileage than narrowbands.  Unplug the o2 sensor, the car should run fine without it if the sensor or relay is your problem.

[bmwman91]

I would check your O2 sensor relay, and your coils first.  Then I would get a smoke machine and find your vacuum leak.

Your o2 sensor could be worn out, widebands last mileage than narrowbands.  Unplug the o2 sensor, the car should run fine without it if the sensor or relay is your problem.

Haha well, the O2 relay no longer resides in the car.  A 2W 1k resistor is jumping a couple pins where it was to provide power to my LC-1 controller.  I popped it out and that made no difference, suggesting vacuum leaks.

The coil packs MIGHT be going, or a spark plug.  I pulled the plugs a couple days ago and they looked perfectly proper...none had more fouling than the others, all were black just around the base and white/green splotched on the prongs.  If it had been ignition related, I think misfires would have been noticed.

I ordered up replacements for every single hose related to the PCB system, evap purge, and idle air.  Most of the stuff is at LEAST 5 years old, and some is cracking a little.  I got new intake manifold & TB gaskets, plus fuel injector O-rings on the way.  The O-Rings have not been replaced at all, and the injectors have been in & out a few times.

Any suggestions on lubricant to use when inserting them?

[sheepdog]

I would double check your connections to thd o2. You may be getting an intermittent short or broken wire.

[bmwman91]

I'll double check.  There is an Innovate Motorsports LC-1 WBO2 unit in there right now, and I would think it would toss codes at me if something was wrong there (hell, sometimes it does!).  Still, could be part of it!

[bmwman91]

Caca, replacing all the vacuum lines didn't fix it (although it does run a little smoother all around now).

Sooo, I suppose the EGO sensor is the next thing to mess with.  I am thinking of buying another weld-in bung and moving it back like 4" to help keep it from heating up as much.  We shall see how that goes.

[mgold]

When I first got my 318iC back in '99 I developed a vacuum leak that ended up fouling my O2 sensor.  Turns out it was a leak in the intake manifold gasket (I can't recall which specific gasket as it's a two-piece manifold).  Hope this helps.