Hi everyone,
Looking for some technical insight on my 2019 Lexus NX300 (87k miles). I’ve been dealing with a rough idle/shaking at stoplights and a 3-second delayed start.
Current Codes:
- P219C (Cylinder 1 Air-Fuel Ratio Imbalance)
- P0172 (System Too Rich - Bank 1)
- P0301 & P0302 (Cylinder 1 & 2 Misfire)
What I’ve already done:
- Replaced Battery and all 4 Spark Plugs (OEM).
- Swapped Ignition Coils from 1&2 to 3&4. The misfire codes DID NOT move.
The Weird Part: I took the car to a second mechanic today while the CEL was on. As soon as I pulled into the shop, the car stopped shaking and ran smoothly. The mechanic couldn't find a "live" fault because it was behaving perfectly. He cleared the codes and told me to come back when it fails completely.
HOWEVER, on the drive home, the shaking started again at red lights (though the CEL hasn't popped back up yet). It seems to happen only when the engine is in a specific state or after the computer finishes its initial relearn.
The "Scary" Evidence: A previous shop did a Cylinder Leak-down test. Cylinder 1 showed 25% leakage (Input 100 PSI, holding 75 PSI - see attached photo). They quoted me $9,100 for a new cylinder head.
My Theory: With P0172 (Too Rich) and P219C, I strongly suspect a leaking fuel injector on Cylinder 1. It would explain the delayed start (fuel pressure dropping into the cylinder overnight) and the rich condition.
Questions:
- Why does the shaking disappear at the shop but return after clearing codes/driving? Is it the ECU struggling with fuel trims?
- Can a leaking injector cause enough carbon buildup to show 25% leak-down on the valves?
- What is the next logical step? Forced cleaning of intake valves or just replacing the #1 injector?
I'm trying to avoid that $9k bill. Any advice is appreciated!