99 Rx300 Cylinder Misfiring

[Cabad85]

Thanks in advance for any comments/answers and suggestions.

Hello all! I'm new to the forum and I have some problems with my 99 RX300 with about 69500 miles. Just a little background, I had just changed my oil 2 days ago and checked fluid levels, which were all fine. I replaced the A/F ratio sensor before the catalytic converter about 2-3 months ago when the CEL light came on saying that the sensor had failed. Yesterday, while merging onto a major highway, the CEL came on, then a few minutes later, it started blinking and when I was accelerating to about 55-60 mph it started stuttering, so I eased off the throttle and it ran fine at about 42 mph. However, it was running at approx 2750 rpm which is too high for that speed. I suspected that the engine was misfiring, also idling was rougher than normal, which also lead me to believe it was definitely misfiring at least 2 cylinders. I went to get it scanned and the following codes were displayed:

P0300: Random cylinders misfiring

P0304: Cylinder #4 Misfiring

P0305: Cylinder #5 Misfiring

P1300, P1305, P1310, P1315, P1320, P1325: Igniter Circuit Malfunction 1-6

Now my questions are:

1)Is cylinders 4+5 by the firewall or by the radiator?

2)Could it be just cleaning the IAC valve, MAF sensor, or EGR valve?

3)Should I just go ahead and change all the spark plugs or the coil packs?

4)I drove about approx. 50-75 miles with this problem, this could not be helped. Do i need to worry about my Catalytic converter?

Again thanks for any input!

VR,

Chris

[tmastres]

Hey there,

cyls 2,4,6 are in front and 1,3,5 are in the back. If I were you I'd clear the codes and then as soon as you get the CEL shut it off and read the codes again. I'd do this because if its a singe coil or plug gone bad you'll get that code as well as a bunch of others caused by the engine trying to run on five (or fewer) cylinders and over a few miles and causing other problems. The first code is generally the legitimate one and the others should(might) clear up once the true offender is repaired. Judging by your list, IMO its most likely a problem with #4, my guess is bad coil. I'm no pro though, just looks a lot like what I've seen from my own experiences. Let us know wahat it was. Thanks