JimNPhx

2000 RX300
Came to a stop light yesterday and all of a sudden started running rough. 3-5 mins later check light came on (flashing).
Today I took it to Autozone for code reads. Random misfire (P0300), cylinder 4 misfire (P0304) and cylinder 5 (P0305) error codes showed up.
All 3 state problems could be:
vacuum leak
fuel system
ignition system
engine mechanical

Since this started I now get 10 mpg

When I first start car check light is on all the time. When I start driving it starts to flash, then solid, then flash.

Before I take this in does anyone have experience with this? Can Itrouble shoot more first?

Thanks in advance

Jim

hypervish

One of the coil's or multiple coils have failed more than likely. You can try switching the coils around, but it'll be hard since these are on the back side of the engine.

JimNPhx

Thanks but I have no idea how to do this, nor have the tools. If this is what the problem is, what is a good estimate on cost to repair?

Thanks
Jim

sktn77a

iTrader: (2)

At a dealer you're looking at $350 for each rear coil. With a bit of luck it'll only be one coil (the code reader sometimes gives more than one cylinder when there is only a single bad coil).

I wouldn't drive the car any long distance while its misfiring like this.

Lexmex

I thought the coils were less expensive than that...perhaps $125 each or so at the dealer.

Anyway, the problem coils would be that of cylinder 4 (front center coil) and cylinder 5 (rear right coil).

See my spark plug DIY, https://www.clublexus.com/forums/rx-...-patience.html that shows how to get those coils off (it's just a 10mm wrench).

If you are facing the engine, the coils go in this sequence.

Rear Left: 1 3 5 :Rear Right
Front Left: 2 4 6 :Front Left

Front ones are closest to the front of the vehicle (the ones you see when you take off the engine cover).

This is actually quite simple if you go buy two coils and then just follow the instructions about how to access the two areas where the coils are (doing spark plugs is a bigger PITA, but you won't have to do that).

lexusrocko

Keith:
My RX 300 codes were P0300,P0304,P0306 so they are all the front cylinders. Could this be a vacuum hose defect or a coil? I am another shade tree mechanic with some mechanical skills but can repair fairly simple items.

lexusrocko

A great RX300 1999 with few problems but when I push down on the pedal the engine misfires & loses power. I can accelerate slower and drive 75MPH, but when I try to accelerate the engine misfires. I took it to auto parts store for new MAF but their computer showed error codes P0302, P0304, P0306 -- Large vacuum leak - fuel system concern - igniition concern .
Obviously all the front cylinders. Any help? And is this something a shade tree mechanic can fix?

salimshah

Follow the vacuum plumbing diagram and most likely you will find an open hose. For smaller leaks, you can spray carb cleaner on and around each vacuum connector and if the engine rpm goes up, you have found your leak. For even yet more precise test, you can have a smoke test performed.

All front being bad at the same time is bit odd. Did the problem happen after timing belt change?

Salim

Stemmer

I had the dealer replace an ignition coil and indeed it cost $400; and that may have been for a front coil. I suggest an indy you trust, especially since it seems likely you know the issue, just not which coil.

lexusrocko

A vacuum leak is what the auto part store thought was the problem. I have a RX300 manual but cannot find a good vacuum hose diagram to help me check the hoses. Any idea where I can pull up a good diagram?
Timing belt has not been changed, and other than misfire on acceleration all else is working okay. Thanks greatly for your help.

cotis

I had the same problem with the back three cylinders reporting error codes. I swapped the coil packs with the front three cylinders, cleared the codes and received the same codes again which told me it wasn't the coils (chances of all six coils being bad = 0.01%). Here is what I found on mine:

I cleaned the IACV in response to trouble codes and rough idle. It did not fix the problem and the codes progressed to show multiple misfiring cylinders, bad O2 sensors, MAF sensor. All the common ones they talk about here. Know what it was? THE OIL CONTROL VALVES (OCVs)! It is the one part on this engine that does not have a feedback loop to the computer so no error codes are associated with it yet when they mess up it triggers all sorts of other codes.

If you are having trouble with your engine and have tried all the "normal" fixes talked about here, change the OCVs and the associated filters! It's the best $200 you can spend. There are posts on the board about how to do this....


Read more: https://www.clublexus.com/forums/rx-...#ixzz2XonIzn41

salimshah

IACV deals with amount of air and fuel to maintain idle (no foot on the gas). I fail to see the connection people are making with IACV and misfire error codes.

Salim

wmjay21

I have a 1999 Lexus RX300 AWD 3.0L.
I rebuilt the engine, it starts & idles fine, BUT has NO POWER, when you push on the Gas Pedal.
ONLY has the following DTC's P0300, P0302, P0304 & P0306 Misfires.

I replace the OCV (Oil Control Valve)
Replaced the Mass Air Flow Sensor
Installed Rebuilt Injectors
Cyl. 2,4 &6 all have Spark
Timing has been Double Checked
Oil & Fuel Pressures are within factory specs

Any suggestions or Help would be Appreciated ??????

benenuf

hey wmjay if you are having misfire code on cylinder 2,4,6 then most likely your problem is going to be that front o2 sensor which is also referred to as a airflow sensor which that sensor control senses air/fuel mixture for those 3 cyls which is the cylinders closes to front of car.