Note: Cross posting from Toyotanation.com to increase eyes on this issue as I am stumped.

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P304 / P303 is being totally elusive. The observed behavior is misfire from 1000 RPM to about 2500 RPM. Once above 2500 RPM or so, it runs fine, no misfiring I can detect. Note: this is the observed behavior when the engine is at operating temp.

One potentially critical piece of information: the misfire DOES NOT occur when the engine is cold. Once it reaches operating temp, it misfires.

Here is the long list of things I have done to try to diagnose/fix this issue. I am at a loss for next steps, any additional things to consider, please let me know, as I think I'm gonna have to go to the Stealership next. Boo!

1. Checked ignition wires. The OHM'ed out ok, resistance, 5, 5, 4, 3 in order of wire length longest to shortest. To double make sure, I snaked wire #4 from my father's 2001 Camry, put it in there, same behavior.

2. Replaced the plugs. Double checked the gap, they are set to what is recommended by the book.

3. Swapped ignition coils. The code did not follow the ignition coil swap. If it was a bad coil, I would have expected it to follow.

4. Seafoamed the engine.

5. Removed the EGR and checked to ensure the pipe is completely clear and not blocked. It was clear, no blockage. I also checked the port where it connects to the engine in back of cylinder #4, that was clear also.

6. Tested the EGR. I put my finger against the EGR valve, used a vacuum pump, and sure enough, the valve opened and closed as expected with vacuum (open) and closed with no vacuum. The EGR valve opened at around 2 in/Hg of vacuum pressure. Also verified EGR is not leaking, it was able to hold the vacuum pressure.

7. Hooked my vacuum pump up to EGR vacuum port at top of EGR valve, and whilst the engine was idling, I pumped vacuum to about 5 in/Hg , engine started running real rough, eventually stalled. This verifies the EGR valve is indeed working and the passage is not plugged (which was also confirmed when I removed the EGR valve/pipe from the engine in step (5).

8. Measured EGR valve pressure during a road test - I tee'd in a vacuum gauge and put a long piece of hose so I could have it with me in the passenger compartment. During normal driving/lite throttle activity, I measured about 3 or so in/Hg, which, from step (6) is sufficient to open it (noted it would open at 2 in/Hg of vacuum). I am declaring the EGR healthy.

9. Verified correct behavior of the VSV (vacuum switching valve). I took the "Q" vacuum hose from the vacuum modulator and connected it to my vacuum pump, then disconnected the host at the EGR and put another vacuum gauge there. I pumped vacuum up to 5 in/Hg and the vacuum gauge connected to the EGR hose matched the pressure exactly. Then, I energized the VSV by turning on the ignition of the car and the vacuum measured at the EGR hose dropped to zero as expected. I'm declaring the VSV "healthy"

10. I spliced ports P and Q on the vacuum modulator, started the engine, and put my finger gently against the diaphragm in the EGR. Observed the EGR valve opening around 2000-2500 RPM.... this would indicate back pressure to be ok.

11. Checked Ports P and R off the manifold. P showed gradual increase from 0 in/Hg at idle to about 20 in/Hg at 3000 RPM. Port R also behaved as desired - goose the throttle, it showed instant positive vacuum. Slow increase in throttle showed little vacuum until higher RPM.

Things I have not done yet, but based on the observation it does not occur when the engine is cold, I am not sure these are even worth doing:

- Replace fuel filter
- Measure fuel pressure
- Compression test (going to do that one today)

 

No takers?

 

This forum is dead. All spammed up and no one is doing anything about it. Good luck with your issue. Toyota nation is a good forum.

 

Year of car?

 

2001 Camry
2.2 L 5S-FE engine