fairmaidon

I have a 99 RX300 that I purchased in 2005. Over the last few years I've had multiple problems and repairs:
1. O2 sensors
2. Bank 2 coils have repeatedly needed replacement
3. 2 of 3 cat converters were replaced last summer.
4. intermittent knock sensor code with CEL lit and/or sometimes flashing
5. Steadily been using oil - synthetic

This week, I traced a new roughness to a misfire code for coil #1. Since I do not have the skills needed to replace coils and plugs 1, 3, & 5 (might has well replace all 3 while the manifold has been removed), I was on my way to the mechanic to have this issue resolved when the oil pressure light turned on, bigger oil leakage, and the car shutdown. I had it towed the rest of the way. The mechanic says that engine roughness resolved with the replacement of bank 1 coils, and it ran smoothly during an in-bay check. However, upon road testing, he came back with a knock sensor code (remember it has been intermittent) and the oil pressure light has returned. Now he thinks that the car has a sludge issue.

I have combed through this very helpful forum looking for answers or even the next step to repair my beloved "Lexi." Any help or suggestions would be greatly appreciated. Thanks

fastnoypi

when have the plugs been last replaced? Roughness can also be contributed to too wide a plug gap from very long term use. No need to spend on expensive coil packs when plugs could be the issue.

fairmaidon

Thanks for your reply, fastnoypi. The roughness was resolved by the changing of the spark plugs and and coils - no new codes on this issue.

My greatest issue is the possibility of sludge. How can I determine if my car does indeed have it? If yes, is there anything I can do about it? Is worth putting more money into it?

And of course, the smaller issue of the knock sensor code returning - even though there is no indication of an actual "knock"

And thanks again.

2KHarrier

Fair;
Here's a rather lengthy thread on the reengineered rear valve cover and some great information on what to look for with engine sludge.

https://www.clublexus.com/forums/rx-...lve-cover.html

It's a long read, but extremely informative. The quick and easy would be to pull the front VC and look for obvious signs of sludging, and go from there.

Grab a samich and start reading...

2KHarrier

Knock sensor will be a separate issue. No doubt the harness going to the sensor is cracking from heat and not the sensor itself going bad..

Here's another good read for you;

https://www.clublexus.com/forums/rx-...ement-diy.html

fastnoypi

You can take an indirect educated guess by pulling off your front valve cover to check for sludge. I would assume if you saw any under the front cover there would be some sludge in the back.

The front cover only requires you to remove the coil packs and 8-9 valve cover bolts with a 10mm socket.
I happen to have a brand new front valve cover gasket with spark plug tube seals left over from my valve cover replacement 2 weeks ago. Feel free to message me if you would be interested in them.

fairmaidon

Hey! Just wanted to say thank you for the advice. We are gonna do a little exploratory work based upon your recommendations. I'll let you know what we find.

Also, if I have some sludge, what are your thoughts on Auto-RX?

2KHarrier

It seems to work pretty well with this engine. I used it when I did the rear valve cover on mine, just to make sure I had a fresh start with everything. So far so good...

Depending on how bad the sludging problem is, you may need more than a bottle of Auto-RX. Most common cause of sludging is the breather system becoming clogged from oil drawn into the intake through the PCV valve. Make sure the engine is breathing well, and keep it clean. If the sludge has effected the oil pick up screen in the pan, you'll have to pull the pan and clean the screen as well..
The Auto-RX will help, but it's not a cure all.

I'm sure others will chime in here with additional advice.

fastnoypi

I would use seafoam or marvel mystery oil over Auto-RX if you have light sludge. IMO, Auto-RX is a bit more aggressive and may loosen a chunk of sludge and clog a passage way or filter.

As 2Kharrier noted, make sure the engine is breathing well. Get your oil temps up high during your flush process by long highway drives and drain warm. Use a high detergent oil during your refills.