You have to try to isolate the area of the Air Intake System where Un-Regulated Air is escaping the Detection of the Sensors that control it and regulate the right amount of Fuel Spray to *MIX* in with it. THIS Engine is
NOT controlled by means of Fuel Regulation.
So anything in the Air Stream that is
*Sneaking in any EXTRA Oxygen* that also manages to bypass the ability of the PCM and/or BCM to Sense and Control things for the BEST possible measurable Stoichi-O-Metric Balance of 14.7 Parts of Oxygen to 1 Part Fuel Ratio
...will *Bump* a P-0300 LEAN CONDITIONS Code....and then?.... JUST WATCH THE MISFIRES COUNT UP!
Start at the Very FRONT of the Motor ...
and look for the following potential problem areas:
(1) Damaged - LOOSE PCV Elbow Hose under the Air Plenum
(Or a Loose Brake Boost Hose?).
(2) Loose S/S Clamps holding the Plenum Air Box to the Throttle Body.
(Collapsed Air Filter?)
(3) Loosened Trapped 10mm Fasteners arrayed around the Intake Manifold.
(4) Loose or Poorly installed MAP Sensor, located at the Upper Rear of the IM.
(5) Stuck Open SAIS Solenoid (if SAIS is part of your 2004 Engine Management System).
(6) Rodents Chewing on Harness Wiring and Connectors can cause Intermittent Problems.
(7) FLATTENED OUT Three (Six Ports) Figure "8" Intake Manifold Gaskets.
They should be *PLUMP* enough to Seal Properly.
Caution:
Use ONLY 89 Inch Pounds of Tightening Force on the Ten IM Trapped Fasteners!
Traces of Motor Oil Dripping Down below the Intake Manifold Flange on the Driver's Side of the Motor are a Sure Sign that the Intake Manifold Gaskets are allowing Motor Oil ingested from the Upper Engine in through the PCV Elbow and Air Plenum then into the Throttle Body and down inside each Intake Port Runner to seep past the Failing or LOOSE IM Gaskets. If Motor OIL can Seep and Drain OUT...
then Un-Regulated Air can get SUCKED IN.
What is NOT obvious is that the IM is partially held in Balance by the Weight of the Throttle Body on One Side... and diagonally... by the Weight of the Cast Aluminum PCM bolted on at four places on the outside of the Intake Manifold on the Other Side. The Black Plastic Intake Manifold tends to Rock Back and Forth in between these Two Masses; especially during times of "Idling in Park" or when "Stopped in Gear at Red Lights".
This tends to Wear Out and FLATTEN the ordinarily "PLUMP" Intake Manifold Gaskets over as much as 240,000 Miles of activity. The Contact between the Intake Manifold's Plastic Flanges and the Solid Aluminum Ports on the outside of the Engine Head are
NOT "Solid State". The Black Plastic Intake Manifold
Literally FLOATS upon the "PLUMP" IM Gaskets and the Rubber Grommets surrounding the 10 Trapped IM Fasteners!
When this happens... these motions can cause a Pendulum-like action to ensue that will either relieve the *squeeze* pressure on One Side or increase the *squeeze" pressure of the Old IM Gaskets on the Other Side
(Top or Bottom) especially when Idling on BAD MOTOR MOUNTS. Thus, this Motion of the Intake Manifold is in Reaction to that "10 Herz Engine Vibration"
@Mooseman mentioned as
THE Big Indicator of having Bad Motor Mounts.
THIS is precisely why most "Idle Stumbling" and the *Shuddering* is so much more in evidence under these two circumstances because the Engine is also operating
UNDER THE GREATEST VACUUM AT IDLE ...and
NOT when traveling at Highway Speeds at Much Higher RPM. And, because it's a TOTALLY Asymmetric Phenomena... the Intake Manifold Air Seals can be Leaking Un-Metered Air into the Engine from
anywhere around All Six IM FLATTENED Gasket Port Locations.
Diagnostic Approach:
These Points of Failure can be discovered by either using a Can of Spray Starting Fluid (or Propane) and VERY Judiciously and Carefully Spraying this Highly Flammable Stuff around the places mentioned in 1-6 above... while keeping an ABC Fire Extinguisher close at hand and while performing this Test on the Idling SUV ...Out Of Doors... Well away from People, Places, Pets and any .
..Curious, Nosy On-Lookers.
If at any time during this exercise, you happen to notice an
Increase In Engine RPM... the Leak Point is likely located closest to the Spray Concentration. If you are doing this Test with Propane... be advised that it will NOT take very long to saturate and accumulate in sufficient amounts under the hood to become Explosive in and around anything that is either *Sparking* or... Incandescently HOT. So...Beware letting "TOO Much of a Good Thing" get the best of you.
