'97 ES300, 170K, has had decent maintenance. GF son's car now. He called and gave me a symptom that sounded like transmission slippage, but, upon a road test, I discovered a severe misfire problem.

However, at WOT, it runs fine...as quick and smooth as ever. As you pass a certain throttle opening, it is as if you flipped a switch from 'broken" to "normal". Not being a Toyota expert (more like a babe in the woods), I am assuming when the vacuum drops below a certain point, it is switching from closed loop to open loop. Sound right?

Has a zillion codes for random cylinder misfire, and misfires on cyls 1, 3, and 5, as well as a bad O2 sensor HEATER code.

I'm thinking a bad O2 for the upstream sensor for 1, 3, and 5. But is that the front or rear (firewall) side of the engine? I can find no data -- even on Wikipedia -- for the cylinder numbering scheme for this engine (which I take to be a Toyota 1MZ-FE (right?)

Please give me some hints!

Thanks, folks.

Rick

 

The 97 ES has the 1MZ-FE.. bank 1 (with cylinders 1, 3, and 5) is the bank nearest the firewall. Bank 2 is 2, 4, 6 towards the front of the car. Closed loop is usually anything below WOT. At WOT, it goes into open loop. So if you're getting misfires at half throttle, and nothing above.. you may have a bad TPS (throttle position sensor) or even a bad MAF (mass air flow sensor). You have no other codes stored? Just P0300, P0301, P0303, and P0305? And of course the O2 heater code?

 

First of all...thanks!

I was under the impression that, per EPA rules, cars went into open loop below 5" Hg of vacuum. I can't swear it was absolute WOT where the symptoms disappeared, but it was surely very close. It was like hitting a nitrous switch! You'd never know it had a problem at WOT...runs flawlessly, a point noted (with some glee) by the car's teenage driver!

At idle you can easily hear a severe miss and smell unburned hydrocarbons. I'm worried about melting the cat if I can't fix this quickly.

Yes, those are the only codes, although I didn't record the numbers (stupid me.)

The reason I was thinking that it might be the O2 for cyls 1, 3, and 5 is because there are no codes relating to the other three cyls, and those three are all on one bank. I would think the TPS would affect all 6 cyls, but, again, I know almost nothing about Toyotas. Some other engines I have worked on have had dual throttle bodies but still only one TPS.

I have read some info about some kind of oil valve for VVT being bad, but, from what I can tell at a glance, this engine doesn't have VVT. Am I right?

MANY thanks,

Rick E.

 

The ES didnt come with VVT-i until 1998, so youre ok there. Surely the O2 could be causing your problem, but it'd be best if you could monitor the readings with a scanner.. It may be reading massively lean or rich, then when its at WOT, the ECU disreguards this reading. The heater inside the O2 can cause issues, but usually it just takes longer to heat up, and the car runs better after running longer. The heater is just meant to bring it up to operating temp faster.

While a TPS should effect all cylinders, sometimes it only shows up on 1 bank... again, something that should be monitored with a good scanner. Check your TPS readings, O2 readings, MAF readings.. etc..