I have just been informed by the check engine light flashing that the #4 coil has a problem, code 304,
I have replaced this coil twice before, about 1 year apart. It is my belief that the insulation on the long sleeve that goes to the spark plug is failing due to heat, it's the center cylinder on the front of the engine (easy to change) and gets max heat from #2 & #6.
Has any one solved this problem with added insulation
Note: I'm a retired EE with 60 years of automotive ignition experience. Thank You

 

Where are you sourcing your coils from? Curious if they are from Toyota/Lexus or third-party. While single coil failures have been reported there hasn't been much chatter about multiple failures in the same location in that short a timeframe.

 

are you using dielectric grease on the coil to plug connection? That might help with a possible moisture/ corrosion problem.

 

I will try the Dielectric grease. It makes a lot of sense, Thank You!
I will replace the spark plug also. What is the make of spark plug required for a 2007 RX-350?

 

There are usually small packs of Permatex at the front counters of most parts stores.

 

Hi Folks,
All is well with my 2007 Lexus RX-350 and I now understand the value of dielectric grease.

I replaced coil #4 and spark plug number 4. I coated the edge of the coil boot with a small amount of the grease, and then coated the porcelain part of the plug and fitted them together before installing the plug. Then I removed the coil with ease and installed the spark plug. Another small coating of grease on the edge of the plug boot which pushes all the way down the plug to cover all of the Porcelain and I installed the coil and tightened the hold down bolt, Clear the code with the scan tool and started the car and all is fine. No codes and no missing
.
Thank You folks for the dielectric grease hint.
Note: The new coil was ordered On-Line Monday @ 9oam California time and for less than $25 was sent to me via USPS with tracking, and I received it at 1:30 pm on Wednesday.
The Spark Plug was sourced locally for less than $15 and about $3,50 for the Permetex dielectric grease.

OBTW if you search on Dielectric grease and can understand basic electronics you can learn a lot about the uses and misuses of this GREAT Grease!

 

Be happy that the failure was up front instead of one of those in the rear bank which are a bear to get to. There is a writeup you can search for here at CL should it come to that some day and you wish to DIY.

Am still interested in where you were sourcing your ignition coils and the brand being used. I know there are some cheap ones out there at places like eBay, however, they are not always the best of quality and could have been the reason for the premature failure of the initial replacement module. You might expect to pay twice that amount for a quality ignition coil from an online discount shop like rockauto.com. Denso is usually the default brand part to use in many such Toyota/Lexus applications.

As for the dielectric grease itself, I have been using Permatex products for decade-upon-decade now. Pretty much a product for all automotive tasks and many are available in small single use packs. Using these products are very much second nature and so go unmentioned most of the time. Spending a few dollars goes a long way and can be all the difference. In your case with the dielectric grease it can help prevent moisture contamination and arcing depending on the application as it has other uses than just spark plugs such as most all electrical connections. However, it is not a panacea for cheap parts.

 

I have used dielectric grease for 35 years, both in my former job as a technician and in my cars. It is a great supplement to prevent moisture contamination and arcing

 

I too just ordered a coil for the fourth time. The source for me has been Amazon and the manufacturer is Beck Arnley. I've replaced number 6 twice and now number 2 for the second time. Gonna try the dielectric grease to see if it makes a difference.
I hope that these 60 dollar parts are the problem and it's not something else. I need one right away which is why I ordered it again from Amazon - It'll be here Friday. Gonna go through Toyota or Lexus and pickup a couple spares. I have a feeling that it'll happen again..

 

Hello everyone, I hope this tread is still alive. My RX350 2007 with 70,000 miles has CEL, VSC and track light is on, AutoZone read the code is P0356. How do you test which coil is the bad one? I looked up in youtube the guy said just plug and unplug the connection to the coil and if you don't hear the difference in engine sound then that one is bad. I check the front ones, #2,4,6 they sounded like they were working fine, when unplugged= engine shakes, when plugged back in there was accelerating sound. Any idea to find out for sure which coil is bad? Please help. Thank you. I called Lexus they sell the coil for $105,amazon $57 from Denzo.

 

Usually you can read the codes example P0305 would be the coil pack in cylinder 5. If you don't see that could look for secondary or pending codes with that breakdown

 

The P030x codes refer to a misfire on a cylinder.
The P035x codes refer to an ignition coil problem.

The op has a bad coil on cylinder 6.

 

Thank you very much Thomas and Dennise for your response.I ordered Denso from Amazon Will arrive on Monday so I hope I can fix it. Lexus wanted $145 just to diagnose it.crazy. thank you agai, gentlemen.