sktn77a

iTrader: (2)

So, my son calls me yesterday and I ask him how the car is? "Oh, the yellow light is on again and it's running rough".

So, I had him bring the car home and got out the code reader - P0300, P0301, P0304. Now I just had the number 4 coil replaced in December (and the number 5 coild was replaced a couple of years ago), so I'm guessing it's the number 1 coil (only feels like 1 cylinder misfiring). Back in December, though, I was getting fault codes on 5 of the coils (only 1 of them ended up getting replaced), so I'm wondering if there might be another problem that manifests as one or more bad coils on the reader?

Anybody got any ideas?

Lexspeed

It could be a number of issues; a faulty coil just one of them. A P0300 is a random misfire and many things could cause that. I had a pesky PO300 in another vehicle and it took me a long time to eliminate all the possibiities before I discovered the problem. Other than these codes any more symptoms to report?

P.S. My kid is a UNC grad.

sktn77a

iTrader: (2)

Thanks Lexspeed: No, nothing else unusual. Based on his description, I pretty much knew what the code reader would say. I'm just wondering if any other cause could be responsible for the cylinder 1 misfire. What was the cause of your problem?

Lexspeed

What causes a cylinder to misfire? Basically, it's one of three things: loss of spark; the air/fuel mixture ratio is too wrong to ignite; or loss of compression. First check your electricals to ensure your getting fire; check the plug, plug wire and coil. It sounds like you know to do that. Regarding fuel, a weak FP or clogged fuel filter could be the problem. Hopefully, it is not a mechanical issue like compression loss or vaccum leak.

The pesky PO300 I had was on one of my toys a 97 SS Camaro with a highly modifed engine (383ci stroker w/386rwhp). I had an intermittent short in my MAF wiring.

sktn77a

iTrader: (2)

Well, it was the #1 coil. That's 3 in less than 2 years. $350!!!

I guess you gotta pay to play....................

Lexspeed

What spark plugs do you have? What is their condition? What is your mileage? The condition of the plugs could affect the coils.

sktn77a

iTrader: (2)

142000 miles on the car. Spark plugs changed for iridium plugs at ~100,000 - dealer pulled one to check and said it looked fine.

Lexspeed

Sounds like you can rule out the plugs. Those iridium tipped plugs made a believer out of me. I changed the RX OEM plugs out at 115k miles and they looked nearly perfect and had the correct gap. If I hadn't already purchased new iridium plugs, I might have been tempted to simply reinstall the oems.

Perhaps you have just had a spell of bad luck with your coils.

gator339

My RX 300 (yr 2000) recently got serviced because of check engine light-on. It turned out the Number 4 coil is bad. My RX was service-done with a few other items such as mechanical problems (steering pump was leaking and two others). When I was picking up my RX, I was told by a service adviser that two spark plugs are not genuine Lexus (toyota) part and charged me. I told the adviser that the 100k service was done here and after checking the record in the computer system, the adviser adjusted the chargefor two new spark plugs and apologized me that one technician who left the dealership used not genuine spark plugs.
One day later I picked up my RX from the dealership CEL came back. I was waiting in the rounge for one hour to see what kind of code my RX is showing. The service adviser told me the code is coming from the oxygen sensor #1, which was replaced by another Lexus dealer, and one technician reset the CEL and doing test driving whether the CEL is coming back or not. I came home and I received a phone call from the adviser, who said the technician was still doing the same test driving. I went the dealership, and watched one technician was driving my RX off the dealership to test drive again. In the end, I picked my RX and came back, started thinking about the problems occurred after 100k service. I had misfiring problem and cold start problem, one valve problem. and most recently the number 4 coil bad. This problems are at least with four new spark plugs and two old spark plugs. I determined that because my RX had two (not genuine) spark plugs, I had such problems. I called the service manager who apologized me that it was "a mistake" done by former technician and he told me that the number 4 coil is nothing to do with "not genuine" spark plugs. I called the Lexus Customer (Lexus National) service to report this experience and I am waing for a phone call. Meanwhile I called the general manager of the Lexus dealership. I told him what I learned and he told me that he would investigate and call me back. He called me back and told that the former technician did not replace all the spark plugs when my RX was done for the 100k service. Since the former tech did not replace two spark plugs with new ones, those spark plugs are genuine lexus spark plugs (but old ones). I believe with my physics and electricity knowledge that all those above problems are related and caused by two old spark plugs and I asked the general manager to reimburse all the repair cost for the above problems I had spent for and he has declined. I am still waiting for a phone call from the Lexus National. What should I do at this point? Any suggestions?

code58

Sorry Gator but it's difficult to sort this story out.