I've got an 02 camry V6. It's been running pretty well up until today. I started it up and it was quite rough, and the check engine light came on. I opened the hood and noticed that the top engine mount was broken. I replaced it, but unfortunately that didn't fix the issue. I plugged in the OBD reader and I had error codes P302 and P303, misfires on cylinders number 2 and 3.

My friend recommended that I change the spark plugs. It's probably a good idea considering it has 145k miles; I'm not sure when the plugs were last changed. But I can't imagine that's the issue, it would be too much of a coincidence for two plugs to go bad at the same time. He also told me that the O2 sensor(s?) might be bad. This seems more plausible to me. In addition, my battery died about a year ago, and after I replaced it with a new one, when I started the car it couldn't hold an idle. After driving it around for ~15 minutes, it fixed itself, or it at least compensated for a malfunctioning part or a leak. It's possible that the sensor was going bad then and now it's worse and the car is no longer able to make up for the malfunction. Either that, or maybe there's a real leak that has progressed.

What do you guys think? It runs, but it's very rough. Acceleration is not great, and there's a lot of vibration.

 

The throttle is electric. Disconnecting the battery will cause the engine computer to relearn what correct idle speed is. Until it relearns the proper idle the engine runs as you experienced

Speculate a ignition coil is bad. The one for the 2/3 cylinders as noted by the trouble codes. Best to replace all coils with a quality brand product.

If the check light starts to blink return home, etc and stop driving. The blinking light means the fuel mixture is too rich and the result can be destroying the emissions converter due to becoming too hot and melting..

 

Don't you think it'd be a miraculous coincidence that both the ignition coils for cylinders 2 and 3 would fail at exactly the same time?

 

Any other codes, vacuum leaks, low fuel pressure, problem ETC sensor, loose wiring connections, MAF sensor.

 

To my awareness, no. There are no other codes displayed.

It's possible there are other issues but none that are blatantly obvious. However, that's why I mentioned the thing about the inability to maintain idle after I changed the battery. I would think the factory settings for air/fuel flow values should be appropriate for the car to maintain idle. Since the battery replacement caused the idle to go out, isn't that a sign the ECU was previously compensating for an issue (e.g. maybe a vacuum leak)?

 

My opinion is not in this situation.

The idle issue happened a year ago with a battery change. The idle speed worked itself out quickly as was normal.

The engine ECU can increase or decrease the air/fuel ratio outside of normal parameters but this is usually a result of a failed sensor such as the A/F, MAP, coolant temp, etc.

It happens engines suddenly have engine operation issues. Thus look for what could fail suddenly such what was listed in the previous post.

These codes cover a lot of possible problems.

A bad A/F sensor can cause the fuel ratio to become far too rich or lean.

Code be one ign coil but two codes. Try moving a coil and determine if the code change to the new location.

 

Well it turned out to be the number 3 coil. I swapped it to number 6, but I continued to get the error code on number 3, in addition to the new code on 6. After some more swaps that continued to point to that coil being bad, I did indeed replace it with a new one and the problem was resolved. Looking back, I think I might have forgotten to clear the error codes after the initial swap 🤣

Thanks for the help!