This is my mothers Lexus, but I drive it from time to time when she needs to go places.

The car has a few issues that i want to address. It has about 95,000 miles on it.

First the engine vibrates a lot in Drive. I’ve clean the MAF sensor including the IAC valve without any luck. Replaced the spark plugs, and threw in some fuel treatment as well.

Also I notice that the idle gets rougher and drops when the headlights are turned off, but while they are on, the idle increases slightly and the engine smooths out a little bit better, but it’s still rough.

Turning the steering wheel in a parking lot also causes the engine to drop in rpm’s and vibrates the whole car.

The ride is extremely rough, harsh, loud, and bouncy, this has to do with its tiny wheelbase and short suspension travel I am guessing. This Lexus only rides fine when the roads are completely flat and smooth, but god forbid there’s any potholes and uneven streets, this thing punishes you! Does anyone recommend better riding softer tires for these cars? Almost want to replace all the struts with non OEM softer riding ones.


The 300 has like 1 year old Firestone Destinations tires on them at at the moment. Not sure if they are made for comfort or not.

The engine struggles big time on hills. I have to turn off the A/C because the engine has such a hard time making up hilly streets. This transmission sucks, this thing definitely needs an extra gear because it’s hard to maintain 65-70 mph at times, again, it struggles to at higher speeds.

Do any of you have similar issues with your RX300?

I feel like something is not right with the engine vibration and power loss. I mean the engine has 220hp but it feels more like 140hp, maybe that’s due to the heavy weight of the RX300 FWD which is around 3750lbs and almost 3900lbs with the AWD?

No CEL on, and she does need to get the timing belt replaced soon.

 

First gen RX is pretty capable machine, but not a sports car. It should be adequate for normal use and expectations. If you are expecting or just stepped out of a hot rod, you will be disappointed.If it was not then it would never have been the most selling model/line of Lexus. Keep in mind this model is not well suited to be driven 80MPH on highways ... it was more for 65MPH.

For CEL, I would still say connect a reader and ensure that there are no engine codes. The bulb can be blown or disconnected.

After the actual read of the codes, I would suggest check the IACV [typical issue with aging first gen RX]. Is your idle 750 rpm?
How old is the gas?
Is the vehicle garaged and protected from critters?
What is the tire pressure ... cold first thing in the morning?
Engine transmission mounts may be broken/torn.
Where are we in maintenance ... air filter, oil changes, transmission drain-fill, brake fluid replacement [Awd extra stuff] .. suspension check. Spark plugs may need changing soon
Quality of tires?

Salim

 

Not my experience with the car at all. My 1999 AWD has 346,000 miles and runs smooth.
I did about 100 miles today, speeds 65-75 mph, no issues. I think it runs at about 2900 rpm at 70 mph.
No problems on hills. No bouncing. No engine vibration.

Sounds like you have some issues to resolve.

 

Thanks guys. Yes the spark plugs were replaced with the OEM Denso’s.

I change the oil for her myself, and I only use full-syn oil such as 5W-30 Valvoline Extended Performance and or Pennzoil Ultra Platinum when it’s available on Amazon.

The air filter was replaced about 3,000 miles ago. Coolant is fresh, everything looks to be ok. There’s no leaks of anything either.

I also drained the transmission fluid probably around 3 times already just to make sure it’s super clean. The previous original owner did a good job at maintaining the car when she bought it so it’s not in rough shape or was abused in any way.

I’ll most likely take it to a shop for her since I rather have a tech be able to test and diagnose what’s going on with it. It’s not AWD, and the tire pressure cold is a perfect 30 psi.

The ride quality is terrible IMO for a Lexus. I live in CA so our roads and freeways are in really bad shape. I feel every bump and uneven street surfaces in this thing.

Compared to her old 04 ES330 she used to own, that thing was like driving on a cloud. Did Lexus stiffen up the suspension in 2003 models? I read somewhere on here that Lexus made the towing option standard on the 2003 MY’s, is this true?

If so, this could explain the harsh ride. I told my mother she should consider replacing the struts with aftermarket Monroe’s or KYB’s that a softer spring rate.

These RX300’s are tough and solid feeling little crossovers. I’ll give it that. They feel very tight to drive with zero rattles. The build quality and fit n finish on these first gens was much better than the ones that came afterwards. It’s just the ride quality is horrible and the lack of power from the 3.0 V6 is a problem since I live in an area where there’s a lot of hills.

 

Where did you buy them? Almost all are fakes including on Amazon.

Have you checked engine mounts?
Same. This generation RX is extremely solid, drives great has good power. Engine is smooth and bulletproof if you change the oil.

 

Got the plugs from Rockauto, and I do need to check the mounts. They are notorious for going bad on these engines. The gas is always fresh and I added a bottle of MMO and some Gumout fuel treatment additives to see if it would help smooth out the engine, but that didn’t work.

Can anyone explain why the idle drops low when the headlights are off? Vise Versa, the idle increases when headlights are on? Even when rolling up or down the windows, the engine idle will drop big time due to the power draw.

I did replace the alternator with a rebuilt Denso unit, and the battery voltage is a steady 13.5-14 volts while the engine is running. So I don’t understand the heavy power draw and why the idle gets so low.

 

I would start here.

So you don't have any voltage droop when when turning on electrical stuff? The ECU is programmed to adjust when turning on headlights. How are you measuring voltage? Sounds like your battery is not doing the job.

 

For idle issues, please search on IACV. Seems like a fairly common issue at about 75k miles.

The idle is controlled electronically by IACV which expccts the passages to be open and the slug [that is just my name for the passage controller which is spun under magnetic field]. Air being sucked in and unburnt fuel in the exhaust are chemically balanced so a malfunctioning IACV or poor idle does not trigger CEL.

Please share idle rpm.

Salim

 

My 2 cents and somebody already mentioned it. The first thing that came to mind reading your first post above was the battery. When I had my RX300 in Mexico I eventually replaced the stock RX300 battery with an Optima Red Top when I took a trip up to San Antonio. Like night and day. The other thing, and I am noticing it with friends here in Miami is that when it gets hotter...the cars runs crappier. We have had heat indexes that go 110+ here. My 2017 CT is a different animal than the RX300 and I just replaced its battery earlier this year, but also noticed an improvement right after. It definitely sounds electrical in nature.

 

I’ll get my OBII scanner on the car later tonight to see what the rpm’s are in drive and park.

I also thought about the battery being a possibility especially because of the power drain when using the windows, and especially the A/C the engine really vibrates.

The battery died a couple of times my mother said because she accidentally forgot to close the door fully, which left the interior lights on all night.

I had to jump start it for her which worked and the battery has been fine ever since, but when I took the car to Autozone one day for them to test the alternator and battery, they did say that the battery is at 60% whatever that means. So it’s working, but barely it seems. Maybe the battery is putting more strain on the alternator that could explain the idle issues?

I did clean out the IAC valve last year sometime from all the research I’ve done on the forum here which has been extremely helpful BTW. No amount of cleaning helped the idle improve.

I’ll report back with the rpm values. Thanks guys.

 

Ok so I checked the RPM’s in park and drive when the engine was completely warmed up.

The reading where the headlights are off and just the DRL are on, the idle fluctuated between 620-635 rpm’s in drive, and around 650 in park.

With headlights on, the idle was anywhere between 685-710 rpm’s in drive and in park.

So something is definitely wrong with the idle speed. The engine severely vibrated when I had the headlights on, then immediately turned them off, the idle drastically dropped.

Here are some pics of the live date from my scan tool. No CEL, no codes were found as well.

 

If you can charge your battery overnight. This eliminates excessive load. There may be some electrical load issue but lets get the IACV serviced/replaced.
Service your IACV. Take proper care as the screws have tendency to be jammed. Read the DIY.
Confirm the slug can spin freely [DIY has the angle of rotation].
Put it back [replace the screws if needed or desired]

You may like to reset your ECU or let the vehicle redetermine your new normal.

Salim

 

You probably won't like this advice, but it's what I had to do to get my RX to idle smoothly, even after cleaning the IACV. I put on a NEW IACV and bench cleaned the Throttle Body. You would not believe all the brown crap that came out of the TB.

 

Thank you guys for the advice. I will go ahead and order a new IACV because I tried cleaning it before and it didn’t do anything.

I’ll take the advice regarding the throttle body. I’m mechanically inclined, but there’s just some repair jobs I just don’t feel like doing and rather have a mechanic do it for me.

Hopefully this will cure the rough idle.

 

please keep us posted. i have the same EXACT issue you have. idles rough untill i turn headlights on or a/c

I have done everything under the sun to it and nothing has fixed it. New iacv, spark plugs, pre cats, oil control valves or whatever they're called. the only thing i haven't done is one of the air/fuel sensors, ignition coils, and knock sensors but did bypass them just to get o/d back but didn't fix the idle issue.