P0305 rough idle / check engine light (I’ve tried everything). Please help!

Hi everyone,
This is my first thread and I’m really hoping you guys can help me. My son has a 2000 4Runner Limited. I got the dreaded P0305 fifth cylinder misfire code. I replaced all three coil packs. I replaced all six spark plugs with Toyota OEM everything. Drove it again and it drove great to start, but as I drove about 5 miles, parked, started again, it started the dreaded vibration and check engine light came on again. I have not checked the compression, but the car runs great and smooth until it gets warm…. I have not checked for mice eating the injector cables. If anybody has any links to how to do that repair work, please send it my way. Really appreciate any help you guys can give me. What’s my next move?

 

Pull the 5th Cylinder spark plug and see what it's showing. They often tell the tale. See if the tip is unusual.

Now, since it runs fine until warm, and it's consistent...I'm thinking it's one of 2 things.

A bad injector on that cylinder. Swap injectors and see if the miss moves. (check wiring)

Blown head gasket. Get a coolant exhaust gas test (color changing fluid) and test your coolant for any exhaust gases.

Since you don't say you are over heating...I'm hoping for a bad injector.

 

Thanks negusm! Installed 6 brand new plugs. I am thinking the same thing, and have ordered 6 new injectors from Motorwest Performance. Really hoping that fixes the problem.

Can anyone explain why P0305 (misfire at cylinder 5) only occurs once the car gets warm? Why does the injector work fine at cold but act up once warm?

 

If it is a head gasket, the engine will expand the crack in it and the plug will foul. Does it smoke white or blue or black smoke when it runs bad?

If it is an injector, again, heat may cause an issue...usually it's the other way around...the injector starts out rough and gets better. But heat may be causing the internals to stop working. I'm thinking you may really have a wiring issue where the heat is causing a short or high resistance somewhere.

Did you replace the ignition wires?

 

It doesn’t smoke at all, starts right up, purrs perfectly. Drives fine for a bit, then rough idle and then check engine p0305 comes on. I haven’t replaced spark plug wires, but I will do that during this full injectors replacements. Previous Owner replaced head gasket. Hoping that with new plug wires and new injectors, all works out fine…

what plug wires should I buy?

 

Only ever use TOYOTA or TOYOTA supplier parts...especially when it comes to sensors and electrical.

 

Hi everyone, here is an update… I was able to install six new injectors and button up the motor today. I had to buy two new hoses that were too brittle to get back on, or cracked. Long story short after putting it all back together it fired right up, ran great, no check engine light, good power, no rough idle. I drove it for 10 miles or so and it ran great. I also did an oil change with a new filter while I was at it. By the way, the oil filter on the 3rd Gen 4Runner is such a pain in the ass to get out. I purchased an oil filter from Toyota, and then ask them if they had the oil filter, wrench attachment, and they said that they have not had it in years. I had to use large water pump pliers to pull the old one off because it was on too tight. I think my next oil change will be using an aftermarket oil filter with a solid fitting attachment to remove it…. Thanks for the help!!! The injectors fixed the problem!!!