teamfitz

Here's the challenge I'm having…

I have an Rx300 with 80,000 miles. 2003. At 70 mph on a straight, level, highway the vehicle will suddenly lose power for about 30 seconds. No check engine lights. Here's what happens and what I see…

I keep the accelerator steady and speed drops by about 7 mph.
Fuel use indicator goes from ~25mpg to 35mpg!
Engine feels unresponsive but doesn't misfire.

After about 45 seconds the engine regains power and fuel consumption goes back to 21-25mpg.

The problem repeats itself after every ~10 miles.

I assume its a sensor of some sort but there are no warning lights. Oh and by the way the hoses are all correctly connected behind the air filter box.

Help appreciated.
Jim

salimshah

Intermittent problems are hard to diagnose.

I would still connect s reader to see if there are any pending codes.

My guess would be fuel pump on the fritz.

Salim

trhs75

I would trust Salim's judgment before I would trust my own, but consider running some Techron fuel injector cleaner through the system. Couldn't hurt, and just maybe it could help. Good luck!!

salimshah

Mine was clearly a shot in the dark and is as likely a false diagnosis as any, as it is not based on any observation.

Live ECU monitoring may give some leads.

Salim

Z07

IMO the instantaneous MPG isn't based upon a totalizer that monitors fuel pressure or fuel flow so I would put checking fuel pressure at the bottom of the stack for the time being.
(not to mention lack of a Schrader valve makes testing FP on a Toyota a PITA)

The instantaneous MPG is based upon injector pulse width, engine RPM, and vehicle speed.

For some reason the computer is shortening injector pulse width.

If the computer thinks you are running rich it will do this. If the computer thinks you are closing the throttle it will do this.

I do not think that both O2 sensors used for AF ratio would fail at the same time and in the same way. So I would move onto the throttle.

I would start with the throttle position sensor. Key on, engine off, backprobe the TPS. You should find three wires. One will be ground. One will be constant +5VDC. One will be the TPS output and will vary based upon throttle position. I would use an analog volt meter set for 5VDC and check the smooth (emphasis on the smooth) change from almost zero volts at throttle closed to almost 5 volts at throttle open. If you have a nice digital multimeter with trend bar it can be used too but an analog with needle is better.

If the TPS checks out then I would want to know that the computer is seeing the correct amount of air. I would start by cleaning the MAF. But I would only use a cleaning procedure that has been proven for this particular MAF. So google up a MAF cleaning technique. If the computer for whatever reason thought the amount of air entering were lower it would pull injector pulse.

EDIT Are you using a dry paper air filter or an oiled filter? /EDIT

The key here is that you observed the MPG readout increase.

As mentioned above data logging would prove insightful.

Good hunting.

hypervish

MAF Cleaning DIY: https://www.clublexus.com/forums/rx-...-cleaning.html

teamfitz

Z07 - thanks for the guidance. Getting that done might exceed my competency but I'll give it a go.

I cleaned the MAF sensor earlier this year - used the right spray and followed youtube directions - so I know that's clean.

The air filter is paper.

Thanks.

mshumack

I had a fleet vehicle that got some "garbage" in the fuel tank. Every so often it would clog up the fuel pick up tube/screen and cause the engine to stutter (or stall completely) then it would fall away form the pickup tube and the car would run normaly. A fuel pressure gauge would have identified the problem but most of the time the car was running great when it was brought in, or the problem didn't last long enough to troubleshoot while it was in the shop.
Intermittant problems are the leading cause of bald mechanics.