[Steve in Chicago]

OBD-II gave 7 different codes. 4 engine individual cylinder misfire, one generic misfire code, one lean condition code, and one fuel cap loose code.

Cleared error code while engine running. AS SOON AS I PUSHED THE ERASE BUTTON, CAR RAN LIKE CRAPOLA. Instantly.

A boost/vacuum leak will throw MAF-based fueling calculations off. From when the leak first begins, and as the leak gets worse, feedback from the #1 O2 sensor will allow the ECM to learn and adjust long term fuel trims to keep your air/fuel ratio where it should be. The ECM learns to compensate for the hardware failure. That will get you the 5 misfire codes and the lean code.

When you clear codes, you also reset the learned fuel trims back to zero. At that point the ECM is back to delivering straight MAF-based fueling without the learned corrections. The vacuum leak is still causing a lean condition (now uncorrected) and the car will run like crapola.

 

[Steve in Chicago]

Look up "boost leak tester" and build one. Something like that will help you locate hidden leaks.

 

[Steve in Chicago]

Is this the end of bottom one that runs length of the engine then goes underneath to DV? Just inside the passenger wheel?

Yes. That is the bottom end of that hose where it connects to the Diverter Valve. On your year engine, I believe the top end of that hose connects to a solenoid tucked under the intake manifold. If you have a hand vacuum pump, you can check from the top end to see if that line and the DV hold vacuum.

I see a worm-screw clamp where a one-time-use clamp used to be. Someone has taken that apart in the past.

 

[Steve in Chicago]

The intermittent CEL suggests the fault is creating a condition borderline to the limit that triggers the CEL or that the fault itself is intermittent. Or in other words, it could be wavering on the edge or on-again-off-again.

Your 04 AWM has no ICM.

Have you tried swapping the coilpacks around to see if the misfire code moves with the coil or stays with the cylinder?

140,000 on the original O2 sensor? It may be time to replace it. Data from this sensor is used to fine-tune fueling and learn long term fuel trims.

It'd be good to see what your learned fuel trims are. If the Additive value is way off, look for something leaking manifold vacuum. If the multiplicative value is way off, the MAF may be contaminated or bad.

 

[Steve in Chicago]

Fuel efficiency itself is actually fine - this fill-up was better than previous. 24.484/gal most recent tank, prior was 23.869. Have an app that tracks it.

Presumed if the fuel trims were off I'd be getting worse mileage? I did more hwy driving on recent tank so not terribly surprising, but it was still mixed w/ plenty city. Just happened to be going further distances within Dallas than usual.

The MAF measures the incoming air. The ECM calculates how much fuel to deliver based on that measurement (then factors in the learned trim). The engine burns the mixture. The O2 sensor looks at the results. The ECM adjusts fueling based on the O2 sensor feedback.

If the ECM always finds itself correcting richer or leaner, it "learns" this. Lets say it always ends up needing to add 1% more fuel than what the MAF based calculations predicted. It will then set a trim value of Plus 1%.

The system can go out of whack, but the engine management system will do its best to correct and keep fueling optimal. If it sees that it has to implement extreme corrections to keep things on the mark, it will let you know by lighting up the CEL and storing a descriptive trouble code. So you can get a lean code and still get normal mileage because the engine management system is doing what it can to keep everything dialed-in as best as it can.

 

[Steve in Chicago]

The easiest way to get those clamps off is to find the flat end and pry it up with a super small screwdriver or knife blade.

See the clamp on the right in the picture?
If you pry that overlapping end away from the rest of the clamp, it releases the little locking tab holding the two parts of the clamp together.
Then the clamp can be removed easily.

Once you do it that way you'll wonder why everyone says these clamps are such a nightmare.