melschase

I own a '99 RX and have 103,000 miles (sales rep, lots of driving!!!) and enjoyed my vehicle since I purhased it used on 2001.
After meticulous care and maintenance, the past couple of months, I've noticed that during hard acceleration my engine bogs down. It almost feels like it's not receiving the proper amount of fuel and shutting down.
Normal driving is flawless until I push to more than half throttle, engine downshifts then hesitates. You could hear the engine wind-up, but it appears tranny not catching up. It's crazy!!!
Had diagnostics done, everything appears ok...

Would appreciate any input...Thanks everybody and great forum!!!

melschase

I appreciate the insight and the vehicle has a new air filter. I'm pretty handy with autos and the idle is smooth with no hiccups and other than hard acceleration is where the hesitation begins.
You may be right about the fuel filter. Question, do you happen to know where this is located in the RX? If it is not difficult to reach, I may be able to switch it out myself.
Thanks again for your input Derek...wish me luck!

Mel

Fern

Sounds like a fuel starvation problem, however, keep in mind that diagnostics don't account for vaccum leaks or mechanical problems.

The fuel filter is a life time type and is located in the fuel tank. You might want to try Techron in the next full tank. How does the tranni fluid look? What about the MAF sensor.. My previous car gave me all kinds of weird problems due to dirty MAF sensor. Its pretty easy to remove and clean with THROTTLE BODY CLEANER or 99% PURE ISOPROPYL ALCOHOL. Some techies suggest this be done every 2 years.

BTW when you took it to have the diagnostic check, did they road test the vehicle?
Cheers,

Fern

ederny

Fern's idea of Techron is where I would start. Mass Air Flow sensor is another good thing to clean. At 100,000 miles, you may consider new plugs if that has not been done. Could easily be A/F ratio sensor or O2 sensor also going bad.

Can you tell us if it is an engine stumbling or just a low power problem? I'm sure you have tried different brands of fuel and/or premium. If you get a check engine light, read out the code as soon as you can.

joyous

At 100k miles it could be catalytic converter disintegrating and pieces blocking the exhaust flow at high volume.

melschase

I'm going to a local muffler shop and somebody told me they have a device to check the catalytic to see if it needs to be changed.

I appreciate everybody's input and hopefully I can get my RX back to norm! Wish me luck or any other advice would help!!!

Mel

LexRX

melschase, if you haven't already changed them, it sounds like your spark plugs need replacing. At 103k miles you are right at the tune-up period. Old spark plugs will cause hesitation under harder acceleration.

LexRX

Just saw your other thread about engine knocking and see that you have already replaced the plugs. Have you had a full tune up at a dealer?

melschase

Thanks for the advice. I did replace original spark-plugs with Bosch-4's. Did not like the way RX idled or slight "bog" during passing. Talked to Lexus Tech and he claims that 4-prongs are not suited for these sensitive vehicles.
So, I changed them to NGK - iridium and made a big difference during idle and smoothness in everyday driving.
I appreciate your assistance!

LexRX

I agree, I'm not a big fan of multi-pronged spark plugs. NGK makes excellent spark plugs - good choice there.

melschase

Hey Derek,
LexRx thought it may have been the old spark plugs that was causing severe hesitation during hard acceleration. But, they are new and I'm leaning on the fact that it is my catalytic converter as diagnosed earlier in this topic.
Still haven't had time to bring to muffler shop.

But I did post another topic where RX is "knocking" only during acceleration. Engine sounds like it has bad gas or not enough octane. But I always use premium Chevron (techron) and same company's fuel injector cleaner monthly.

Timing was mentioned but I did have it Lexus service at 97K...go figure!

DaveGS4

iTrader: (2)

(earlier post)
Wow, that's a pretty good observation for a soccer mom, Ms West.

ayche

i know you have an rx but i had similar issues with my gs430. thought it might be the cat or transmission pr transmission fluid or fuel pump or bad gas, etc etc. turned out to be a very dirty MAF sensor. Car only had 50k miles on it too, go figure. cleaned that out with throttle body cleaner/MAF sensor cleaner as well as the other plastic ducts before the MAF sensor and car runs like never before! no more downshift problems, no more bogging and hesitation.