tarzan17

When ever I drive my wife's 2000 RX300 I always notice that the vehicle tends to decelerate when ever I remove my foot off the throttle. Feels like a small braking force is being applied somewhere. Is this normal?

OzrkFisher

I feel the very same thing you describe... only I think it the transmission not being warmed up enough to get out of 1st gear... so it revs down.

It feels very much like you are in a descent mode in a fancy SUV on the lowest setting.

Mine is a 1999 rx300. I just had the oil control valve replaced at the dealership. Pray that never happens.

jbl-1985

You need to be a little more specific, I mean, the car is supposed to decelerate after you take your foot off the gas pedal, right?

Most if not all of these Lexus models have something built into their ECU's called slope control, which if you are going down a hill the transmission will automatically shift into a lower gear to help slow the car when you touch the brake. Also, when the RX cold, it will not shift out of 2nd gear until it is warmed up. So you are dealing with a couple of scenarios, which is why we would need more information.

Also, this is probably not the right forum to discuss this issue as it is dedicated to poor gas mileage. I should practice what I preach since I already discussed it...

tarzan17

Thanks for the response but I politely disagree this is the wrong thread.

I will explain.

Assuming I am in D gear and moving on a slight downward slope at 40mph and I see traffic ahead slowing down, I will lift my foot off the throttle (no braking). I immediately feel the vehicle slowing down ever so slightly as if a small braking force is being applied. And as OzrkFisher wrote above, it feels like engine braking. This will definitely affect fuel economy since the vehicle is slowed down. Currently averaging 16-17mpg. On my Odyssey when driving same roads it doesn't happen. I could explain it another way using two bicycles: get up to speed then stop peddling and coast; bike one coasts as expected; bike two coasts but slows down quicker as if the brake is rubbing ever so slightly.

Thank you for pointing out 2nd gear limit when cold. I'll pay closer attention but from what I remember, this happens all the time, even when cruising on the highway.

MellonC00

Most likely it's the function of your torque converter, lower gearing on the Lexus and a combination of both. Nothing wrong with your car. It does drag more than the Honda but the clutch take up is also quicker and more efficient that lagging torque converter you have in the odyssey.

tarzan17

Thanks for the analysis MellonC00.

Think I found the root of my problem; a clogged PCV valve ( and or combination of dirty IACV / throttle body / VSS). First step was cleaning the IACV (without removing) and throttle body then cleaned the VSS. Car drove better but could still feel the drag. The PCV valve has a spring mechanism at bottom of vertical shaft which was gunked up to the point it no longer functioned. After cleaning and enabling the spring mechanism to function again, I noticed right away how smooth the car accelerated and felt overall. Wasn't until completing the test drive that I noticed the drag was gone as well. Haven't been able to quantify overall gas mileage improvement yet.

EDIT: There were no DTC / CEL / pending codes indicating clogged PCV (as a matter of fact, I haven't seen any codes since my A/F sensors went bad).

defo

iTrader: (6)

Mine is low too....averaging between 16-18 MPG

Bobster999

Thank you that was very helpful.

Rezman

Very helpful thread. I was down to about 15.5 mpg, engine was idling at about 1700rpm. Sure enough the MAF sensor was gunked up. Checked the air filter, it was white as the driven snow ( I think Lexus may have replaced it when they put in the new trans a few weeks back.)
I used the CRC MAF sensor cleaner and let it dry while I unhooked the battery to reset the ECU.
Started the car back up and watched over the next few minutes as the idle dropped steadily down to @800rpm. It's much quieter in my garage. Well worth the price of 2 gallons of gas for the cleaner.

Baetke

Thanks for checking back in with your results. Just so you know, your car should idle at 700 +/-50 rpm in Neutral or Park with all accessories turned OFF.
Baetke

bbrentd

My current average according to the MPG reading on the LCD is 18.2. I guess that's about as good as it gets for the RX300

Lexmex

It often just depends on how you drive. I've set my RX300 on cruise control a number of times on business trips from Miami to near Tampa and can get as high as about 27 on MPG, but if I floor it around town you can easily see 16 mpg.

jbl-1985

Probably doesn't hurt that Florida is Flat too!

Baetke

My all time record is 27.1mpg on a tank of gas using cruise control at 55mph I drove from southern Oregon to northern Oregon on I-5 which includes several mountain passes.

Lexmex

The highest natural landform I go up here is about 20 feet, unlike Mexico.