A really excellent write up ! I love the pictures.
I would only a couple of small comments, picked up mainly from experience
(How do you get Experience ? Lack of Knowledge !)
P0401 is frequently caused by a clogged EGR passage from the EGR valve back to the intake manifold. The fastest way to test for this is as follows:
- Start engine
- Attach hand vacuum pump to EGR valve
- Apply vacuum and watch for EGR pintle to lift
- If pintle lifts, but the engine RPM does not drop (or stall completely), the passage to the intake is blocked.
Cleaning the passage to the intake varies from engine to engine. Frequently this passageway exits just behind the throttle body. The "guck" clogging the passage is soft and can be easily cleaned with a rag and a stiff wire. Use a couple of long pipe cleaners (Walmart) twisted together to reach down the passageway. For best results, clean from both ends (throttle body and EGR valve)
These steps should be done first, before replacing any parts.
