LexRX

kRonX, I highly doubt that not using 91 or higher octane gas would cause that problem. Many people use regular and midgrade gas on CL and I've never heard that complaint. Furthurmore, even if you were using regular gas and had that problem, you wouldn't necessarily be at fault since the wording the the owner's manual is stated so that premium gas isn't required only recommended. The problem must have been elsewhere, probably in one of the parts that was replaced.

kRonX

iTrader: (1)

interesting... so is the dealer lying to me telling me they replaced something else intead of what they stated... What else could be related to the idle control valve. What else could have caused it to malfunction? COuld the mods on the car have anything to contribute to this problem? I have a rod millen exhaust and a k&n replacement filter...

LexRX

kRonX, I really don't know enough about the problem (or the RX internals) to know and hate to speculate. I just feel it's a long shot for the mid-grade gas to cause that based on others experiences. As far as the mods go, I have the RMM exhaust and had the Weapon-R Cold Air Intake on for about a year with no problems.

mikey00

kRonX,
I would find another dealer and seek another opinion. Sounds way off base to me.

kRonX

iTrader: (1)

ya... i thought so when i took it in... Sounded fishy. Too late now, everythings been done and fixed and was part of the warranty. I guess the next time for the next service ill take it to somewher else and get a second opinion.

techlover

i am sure higher octane than regular is recommended by lexus for higher performance(horsepower) because the engine must have an electronic knock sensor that retards the timing to the point where it just barely inaudibly pings on 87 octane. hopefully when we put in higher octane fuel the engine quits pinging and the knock sensor advances the timing to the point where it starts slightly pinging again. this is where maximum power is reached unless even higher octane fuel is used. i wonder at what point does the octane stop advancing the timing due to electronic and mechanical limitations. we have 94 octane shell gasoline here in new orleans and although the extra power may exist only between my ears it sure seems to be real. wish a driveability engineer would give us the final word. i sure hate wasting money for octane that does no good. andy

techlover

also i forgot to mention using high octane fuel seems to cause my engine to chirp its tires sometimes in hard acceleration at low speeds and causes a lot of torque steer which is common to a front wheel drive vehicle with a powerful engine for the size of the vehicle. i have a fwd version. my other car is a 2000 corvette so i love it when this little 3.3 liter engine cranks out more power than my vette per liter. what a wonderful car we all have regardless of the octane we use! andy

ederny

techlover, you've almost got it right.

We're all saying there is a performance difference, but can't feel it! What gives?

The key point is that only under wide open throttle (when you put your foot to the floor - especially at low RPM) will the engine actually make the extra power from the hi octane fuel, because the ignition timing is not retarded as much by the engine control as with low octane fuel.

Keep in mind the sensors do work by listening for knock and since knock will only start to occur at the higher quantities of fuel+air packed into the cylinder when you put your foot in it, the higher octane lets the engine produce more power when you are pushing it. At normal highway speeds you will never see it. So no matter haw many Fla trips we take, there is essentially no difference in mileage to be discovered.

So what good is premium? Yes, passing on those mountain roads and entering interstate highways on short entrance ramps in heavy fast moving traffic - you know when you need that max acceleration at WOT.

What's this ignition retarding thing? Engineers designed the controls to fire the spark plug to ignite the fuel/air just before the piston is compressing the mixture into the smallest space (top of the compression stroke). Well "just before" is good for max efficiency, but if the fuel burns too fast (explodes as in low octane), the cylinder pressure goes so high in a still decreasing space it is heard as a sound (knock) and may damage the piston/valves - and power is lost, big time. So, by setting the time of spark a little later (retarding), the piston is more right at the top of the compression stroke or just starting to go down increasing volume, then a fast burning low octane fuel will have plenty of room to "explode" in - keeping in mind this is much more-so the case at WOT and not at highway cruising speeds.
.

HarrierAWD

I personally find high-octane gas useful in the mountains. My RX300 can stay in 4th gear going up a long steep grade with 91 octane. It downshifts less often compared to mid-grade 87 (in Colorado.) On the flatlands it makes no appreciable difference.

kimberlyk2

I've had my AWD 330 for almost 3 months now. I've experimented with 87, 89, and 93 octane. I drive moderately (usually no more than 75 mph highway and posted speeds in city/suburbs) approximately 75% is highway and I've found that the octanes do make a difference for mileage. I haven't notices performance hits/boosts. Each bump to a lower octane shaves off 1-2 mpg from the previous. Currently running 93 I'm getting 22-23 mpg (my own calculations, not computer, which is close to mine - usually within 1 - .5 mpg...). At my worst running 87 octane I got 18 mpg with the same type of driving mentioned above.

*shrug* Is the extra .10/gal b/x 89/93 worth the mpg boost? Eh I've done the math and it's almost a wash. To each his own I guess...

-k