Dropping Mileage And Running Worse

[LVheretic]

Hi All,

I have a 99 RX 300 with about 75k and have watched my miles per gallon drop over the past 2 years... right now, it registers 12.9 - 13.2 per gallon.

There appears to be a smell of gas at the tailpipe, the vehicle bogs down under hard acceleration--then catches sometimes with a small backfire under the hood. Once in a while, it puts out a smoke cloud when starting up.

I changed the plugs and belts about 5k back. Neither helped or added to the problem.

Also, the oil is the wrong viscosity--is this a big problem?

ANY help/suggestions will be greatly appreciated.

Nick / Las Vegas

[SKperformance]

get a motorvac to clean the engine ,sensors and cat

[mtakeda]

Any dark smoke exiting the tailpipe while running?

[LVheretic]

No dark smoke that I am aware of... the problem may be resolved after cleaning the MAF...it definitely runs faster with no bogging down.

The UK Lexus site noted the same symptoms as mine and even had pics of the ultra complicated (ok, not complicated) process.

Whats a motorvac?

[tds]

Other things you can check are your timing (and engine computer) and the igintion coil. It sounds like all of the gas is not burning in the engine.

[tds]

One more thing...I had a car years ago that had this backfire and it turned out to be the iginition cables.

[Sark003]

Check the Maf sensor. It may be on its way out. Not enough to cause a MIL but can cause this exact issue.

[SKperformance]

a motorvac is a machine that is hooked up to the fuel line and pumps a high pressure cleaning solution through the fuel system which cleans it amazingly as well as having the throttle body cleaned as well.

It helps every person who gets one.

[Sark003]

Doing a fuel system service may help some but, If you remove the MAF sensor and examine it, You might find some reidue on the sensor located mostly on one side.