I finally was able to get what I think was a relatively accurate comparison of the effect of greater speed on mileage in freeway driving. I know my mileage indicator isn't precise , but it appears that mileage drops about 2 mpg when I increase my speed from 70 to 75, driving with cruise control.

Is this about what everyone else can observe?

This is on my 2003 SC with 100K miles.

I'm a little disappointed...I thought there wasn't going to be that much difference. But I was somewhat impressed the MPG was 26+ at both speeds.

 

From what I am able to observe with the less-than-perfect mileage indicator my SC delivers about 25-26 mpg at 70 mph on straight and level surfaces with the top up. Perhaps a mpg or two less at 75-80 but sometimes no real detectable difference over that range. Stock 2002 SC with 39K miles and 11K miles on the tires.

 

How accurate do you guys think the MPG readout is to our actually MPG? I get about 19.8 MPG on average with 80% city, 20% freeway. No matter how many times I reset the thing, it always ends up at 19.8

 

Yes, it does seem like 75mph or so is the "sweet spot" or drop off of MPG for me too on my 05 with 37k miles.

 

Not very accurate. If you want to know just how great that indicator is you need to set your trip mileage and do the math when you fill up. On most cars I've owned the trip computer mileage calculation was good within +/- 10%-15% of the actual usage. Interestingly ALL of them have read favorably to actual. Imagine that...

On my indicator it seems to be about 18.6 mpg for the same mix of driving that you reported.

 

I get similar mileage to m3nv of 19.5 mpg. I set the trip computer and checked the mpg after filling up twice. Calculated as 19.4 mpg each time, so the avg mpg compares very well. Not bad for a 2002 with 94k miles. I might mention that it used to be 16.7 mpg until I cleaned the MAF sensor and the throttle body. Jumped to 19.5 and smoothed the idle.

 

Did you just clean the MAF sensor with CRC electric contact cleaner?

 

Yep, I read a couple threads on this site, got the CRC from Advance Auto Parts and VERY carefully sprayed the sensor. I think cleaning the MAF had a bigger impact on MPG's than cleaning the throttle body because I only cleaned the MAF on my RX330 and got improved mileage and smoother idle. Really cheap tuneup. I'm still running the original spark plugs.

 

I just noticed a warning on my CRC Mass Air Flow Sensor Cleaner can:

"10. DO NOT use on vehicles with a Karman-Vortex air flow sensor, e.g. Toyota Supra Turbos, Mitsubishi's and most Lexus vehicles."

Has anybody else noticed it?

 

This same subject is mentioned on the last page of the MAF DIY post:

https://www.clublexus.com/forums/mai...and-gs430.html

But there's no real conclusion to the issue.

 

I read about the Karman-Vortex air flow sensor on the internet and then compared it to the SC430 sensor. My conclusion was that the SC uses a hot wire sensor that didn't look like a Karman-Vortex type sensor. I saw no risk in using the CRC spray, so I took the chance knowing a new sensor runs $117 on eBay.

 

Thanks. I really look forward to this improvement. If all I'm doing is cleaning the MAF sensor, do I need to disconnect the battery?

 

You don't need to disconnect the battery to unplug the sensor and clean it, but it is recommended to disconnect the battery to clear the ECU.

 

I already use the CRC on my car. Now I see this and it makes me nervous:

It (Karman vortex ) is used in some, but not all, versions of the Toyota TCCS engine management system [Toyota Computer Control System]. This can be found on a lot of Supras, in the 1987 to 1992 age bracket, and also the Lexus V8. The only difference between the meters fitted to the different engines is the size of the two main passageways or chambers used in the air flow meter. The Lexus meter allows more air flow through the meter at the same Karman vortex square wave frequency.

 

As far as I can determine the service manual I have mentions nothing about cleaning the mass air flow sensor, but there are frequent references to replacing them as a remedy for a number of symptoms. Doesn't look like there's a lot of guidance unless a service bulletin or other supplemental document was issued. I am wondering if denatured alcohol would be harmful. It's probably not as active a solvent as the CRC cleaner but it may be less risky. Anybody know for sure?