Sudden rough idle, loss of power, poor fuel economy

[YoshiUK]

Hello, first time posting here.

Was looking for some assistance/knowledge from folks who have worked on these cars before. I've got a 2005 Lexus RX300 and it recently started having a bit of a rough idle.RPM sat around 1000, slight vibration in the steering wheel. Additionally she's gotten really sluggish accelerating, and my fuel economy has dropped from the low 20s where it normally sits to 13-16. 

I pulled codes and nothing is posting. My initial thoughts were an air/fuel sensor but wanted to see if anyone else here had run into anything similar in the past. Thanks for any information or assistance you can provide.

[PCM]

MAF?

Quick check at a trusted independent?

Good luck.

[YoshiUK]

Whelp, cleaned out the MAF sensor, but it wasn't too dirty so wasn't that hopeful it would fix it.  Started her up again, cleared codes and re-tested...

 

p0305 cylinder 5 misfire.  So...yay.  it couldn't be one of the front 3 easy to access cylinders could it?  Now hoping it's just a spark plug, not a coil pack, or fuel injector.

[BachelorDays]

If you've got 100k+ on the clock it most likely is the MAF.  Cleaning doesn't fix a bad MAF, just cleans a dirty one.

Live data will show if a MAF is bad.  You'll seldom get a direct MAF code - it's normally misfiring codes that indicate MAF.

[YoshiUK]

BachelorDays what data should I be looking at to see if the MAF is bad?

[YoshiUK]

The MAF output is 3.7 g/s at idle and seemed to be between 38-55 g/s driving

[BachelorDays]

Sorry but I don't know the acceptable range for these values for the RX. The norm is to check at idle and revving up and also the air temperature it's recording.

[BachelorDays]

PS Do check the net on this. Live data also shows MAF voltage patterns on idle and revving up which help in diagnosis.

[GrahamG]

My '06 RX350 eats ignition coils like Smarties. Have ordered Denso coils [OEM] from Rock Auto USA at half UK price, about £57 total each.

There is a You Tube video showing easier access to the rear coils by removing the windscreen wiper assembly which my mechanic tried and agreed was worth while.