Misfire

Hello all. I am hoping that some of you could point me in the right direction for some general misfire issues on my 2001 with 245k miles. For a little while, it has experienced a misfire that only used to occur during warm up, now it appears the misfire occurs more often after warm up, but is still intermittent. Some days the car appears to drive just fine with fuel mileage numbers in the 43-47 mpg range. This resulted in a check engine light as well as the unsettling sound of the planetary gear rattling during warm up. What has been done so far:

• plugs changed with ND iridium plugs 10k miles ago
• plugs changed with NGK copper recently (just to confirm the misfire was not the plugs. I will switch them back to the iridium)
• changed out cyl #4 coil-on-plug (aftermarket)
  • moved coil around still no affect on misfire
• throttle body cleaned
• PCV valve changed (OEM Toyota)
• 12v battery replaced less than 1 year ago with an Exide AGM 51 series
• air filter changed
• confirmed HC valve on catalyst moves OK
• fuel injectors replaced with rebuilt injectors (twice)
• fuel pressure confirmed at 46 psi running
• fuel pump volume confirmed at 1 pint of fuel pumped in 14 seconds (Most injected cars specs are 1 pint in 30 seconds or less)
• compression at about 140-160 psi (cranked at 1000 rpm by turning the key, not the lower scan tool enabled cranking speed)
• manifold vacuum 16 in-Hg (slight 1 in-Hg fluctuation) at idle after warmed up taken from the purge line
• no apparent vacuum leaks (propane testing around manifold)

The manifold vacuum number worries me as this reading would be otherwise low on a traditional Otto cycle engine, but given this Atkinson-Miller cycle, not sure if that reading is OK.

Codes are as follows: P0300, P0301, P0302, P0304, P0420, P0440, P0441, P0446

I know there is an evap problem and catalyst that I will tackle once the misfire issue is addressed. Just worried that this engine is now worn out and time to retire. Your advice would be appreciated.

Some additional information. As the weather turns colder, the car is now steadily misfiring when cold. Codes still show a misfire on multiple cylinders (P0300, P0301, P0302, P0303, P0304). I think I will try making the cold start mixture richer with propane to see if that helps it.

Aside from that, can anyone else with a 1st Gen let me know what their manifold vacuum reading is at idle?

 

Thanks to everyone who responded to this post. Especially Jeff for pointing me to that post. It looks like the fuel filler neck was the problem. This is what I found when I took out my old filler neck. The part at the top of the neck with the fuel goes in was completely rusted away. That is not surprising considering here in New England there is a lot of salt on the roads. What I'm boggled by now is that the new filler neck from Toyota doesn't include a place for one of the hoses that I see on the old filler neck. For now, I'm going to close off the area on the valve where the hose goes. But it would be nice to know what people have done in the past with this "extra hose".

 

Just called the dealer I purchased the filler neck from. I ordered part number 77201–47051. Apparently this is the correct part for my vehicle , however it has been superseded from the old parts number and requires an additional valve 7720–47011. Considering the third hose went to a collar on the filler pipe and ended up being plugged with sand and salt anyhow, I believe I will just block off the old valve and be done with it. If it still said the check engine light, I'll put some sort of filter on it.