First, I want to say that this Lexus Forum is the BEST on the web. Everybody is very helpful with advice, suggestion, and solutions in making our cars run well. Great Job!

My dilemma begins with my '99 Lexus RX300 AWD with 115K miles (sales-driving...) I noticed that during hard (3/4 to full throttle) acceleration my car hesitates. I took the advice of a club-member and replaced my catalytic converter and it helped tremendously. It still hiccups during aggressive acceleration, but not as bad...

My question is can this be because of poor O2 sensors (which needs replacing) or other resistance elsewhere on the exhaust stream? The engine sounds like it revs fine during acceleration, but if I let-up from the accelerator pedal a bit, it appears that it finally "catches" and takes-off...go figure! In addition, I was told that our engines have a Knock-sensor to prevent engine knock. Apparently my car is knocking louder than the sensor is. I use good grade gas (Chevron/Shell Premium) and it still tends to knock.

I love my RX and hope that all this is just simple problems that I can solve with little effort both physically and financially. Hope someone can help!!! Thanks again for your input!

 

I have a 2000 RX300. I noticed that it has 3 converters, did you replace all three or just the one that is bad??? Also could be possible that a piece of metal from the converter is lodged somewhere in the pipe or the muffler (I had that on another car, a loose rusted piece from the converter lodged itself further down the pipe and was blocking air flow). If the converter needed to be replaced already maybe the muffler does as well. Well thats my two cents. Good luck and hope you find the problem.

 

Thanks Jubane,

Actually, I only replaced the main (before the muffler). Why do our vehicles have 3 Cat-converters? I assume that those are the "bulges" coming from each side of the exhaust manifold... I don't know how to check if there are hunks of metal obstructing the flow. How did you get your's checked?

Anyway, I appreciate your help and hopefully it would be as simple as that. Thanks again!

 

It was a 92' Cavalier (my first car) the converter was rattling and I was having acceleration problems. I took it in to get the converter, pipe, and muffler replaced. When he cut the muffler off she found the piece lodged. As far as why we have 3 converters no idea, but I remember seeing those buldges and looked in the owners manuel and it said that it has 3 converters. Two after the manifold and one that goes to the muffler. If I was you I would just replace all three, you already did the main one.

 

Don't mean to scare you, but my 2000 was knocking/pinging about a week and a half ago and (although the service advisor said the two weren't related) it turned out that I had "oil gelling" inside. They replaced the short block and numerous other things, cleaned the entire inside and when I picked it up today, it runs like the day it rolled off the assembly line (minus the "new car smell"). The knocking is gone, too. My first inkling that something was wrong was the fact that I was adding oil every 1000 miles or so. Noticed any excessive oil usage with yours?

 

Acceleration hesitation could be a number of things. Besides the other stuff mentioned, have you checked the fuel filter?

Many modern V6 and V8 cars have 3 cats for cleaner emission.

 

The RX300 has a permanent fuel filter located inside the gasoline tank per Lexus. I thought the same thing but find it rather strange on how that filter can clean itself...

Am I missing another one somewhere in the fuel-line?

 

Oil has been good. Maintaining proper levels using good oils. One problem they claim that the RX's have is "sludging" inside the engine. If this is happening, is there a solution out there that can be placed in the engine to remove this goo?

Please help!

 

There really is no solution to remove the goo, you will have to take your Lexus to the dealer and they will have to replace the engine and other components that might have been damaged. Lexus is aware of the problem and is offering a 8 year unlimited milage warrenty on the engine. I say take it to the dealer pay the $80 it would cost you to do the check and l'm sure they will be able to tell you what is causing the problem you are having., heck you might end up with a new engine at the end of the day

 

The special warranty is 8 years / 80K miles according to the letter I received from Lexus.

The oil gelling and oil sludging problems are two different issues. The oil gelling is due to a faulty modification to the engine. According to my dealer, if I go by the 5K interval instead of the 7.5K interval, the oil gelling can be prevented.

The oil sludging problem is caused by careless or moneyless owners who don't change their oil, or who use snake oil that claims change interval can be extended to very long interval.

Bottom line, change the oil every 5K miles and you'll do just fine.

 

Yeah...like me. I've got a 2000 RX 300 with 56050 miles on the odometer and 87 miles on the engine!

 

I would pull the valve cover to get for gel. The knocking you are hearing probably the vvt-i actuator is getting dry because of the lack of oil. Get it check out quick before you ruin the whole engine!
JPI

 

Use synthetic oil, period.

 

I have been using Mobile 1 - 5W/30 ever since I've owned the vehicle and replace it every 3K-4K miles. Using a good filter and still hear the knocking. Even during light to heavy acceleration, you can still hear the sound. I even put fuel injector cleaner hoping the extra octane will help it, but only very little.

Thanks for the suggestions guys, but that VVT-I module, that appears to be a very difficult & EXPENSIVE project. Can Lexus detect that problem through one of their diagnostic tests?

 

I just checked my oil gelling letter from Lexus and the warranty is 8 years unlimited mileage, not 80K as mentioned above. Also I believe oil gelling and oil sludging is one and the same problem.