thraex

I'd like to start off by saying I come here out of desperation and last resort. Recently I bought a 98 ES300 with ~180k on it. Previous owners treated it like garbage so it became my problem.

I'd also not like to waste anyones time reading useless info so I'll get straight to the point.
My issue seems to be related to the air/fuel mix and I've already replaced and done so much work on the car I'm completely lost at this point.

The problem:

The car starts and drives fine on a fresh wipe (battery disconnected and reconnected) for about 10 miles. Upon next start the idle and acceleration is rough and it sounds like misfiring. The car will lag until about 3k RPM and a wide open throttle when it shoots into power. In worse cases, the car has failed to move, stuttering along with terrible misfires and almost no power, not moving until full throttle. A battery reconnection has saved me from being stranded.

What I've done to try fixing it:

spark plugs, ignition coils & wires, air filter, oil and filter, O2 sensors (Bank 1 & 2), MAF sensor, trans fluid & filter, air box & throttle body inspection, thermostat (+ new coolant), ECT sensor, seafoam(gas),

Originally I was getting O2 sensor codes(P1130,P1150). Ive changed them twice now. (I went cheap the first time) and it seemed to fix it very temporarily. I replaced the MAF sensor but that didnt really seem to do much either. I also inspected the throttle body, air box and hoses and couldnt find any noticable leaks or cracks (naked eye).


As of now, I have a P0125 code. The mechanic said it was probably my thermostat. I changed it, nothing. So I replaced the ECT sensor, nothing. Same code. (note: The temp gauge reaches half and stays there, so the actual temps are normal) It is often followed by pending O2 sensor codes (P1130, P1150 -- the P1150 for bank 2 is sometimes stored) and sometimes misfire codes (P0300, ...) but when I took it to a shop they said they didnt see it (maybe bc its pending).

Whenever I take off and reconnect the battery it runs beautifully, for a little bit. Once it starts running like crap again I've noticed the exhaust smells bad. But that may be from the seafoam in the tank.

I'm so lost, this car has been so back and forth and after all this work its been spewing the same BS.

I can note that after the second O2 sensor change, the car seemed to work fine for about 4 days. But once I reconnected the battery after the thermostat replacement it went back to the same antics.

Any help is dearly appreciated, I know this car wants to do well and has many more miles in its lifespan. I feel like I've already covered so much its something small I may be overlooking.

Anything helps, thanks again.

LeX2K

Clogged fuel filter? Or possibly a bad fuel pressure regulator also known as pulsation damper. Another possibility is the engine is sludged up, any way you can pop off the front valve cover to have a peek?

Terrible running engine with seemingly random issues can be caused by a bad ECU (leaky capacitors) but this era of ES is not known for that. Wouldn't hurt to remove the ECU and pull the cover off see what's up. I'm tossing things at the wall here.

Arsenii

Hello,

What brand parts did you use, where did you get them? Here is a good place to get aftermarket parts.

Coils rarely fail in those engines, and if they do, they straight up don't work, so unless you got Genuine OEM coils, about $120 a piece, or Genuine NTK coils, about $60 a piece, I would put the old coils back in and see if that helps. If you don't have old coils, get some used OEM from junkyard or eBay, the chances of getting an actual OEM parts are much greater, and the price tag is not too bad compared to new ones.

Same goes for MAF sensor, those are very high precision components, I would only trust OEM one to do a good job, so unless you already got known good OEM, I would suggest either using your old sensor, or getting a used OEM off of eBay, they do have a pretty robust return policy if something goes wrong. After that, check MAF sensor readouts while at Idle, they should be about 3.5 - 4 g/sec, if the value is higher, chances are the sensor is in need of cleaning, or is starting to go bad and needs to be replaced. If the values are lower than expected, chances are there may be a Vacuum Leak somewhere in the engine, causing the air to enter the engine around the MAF sensor.

With that, to me it sounds like there is a problem with O2 sensors, even though you replaced them already, it appears that the issue starts to occur right when the car is supposed to switch into a Closed Loop operation, meaning that it has to use MAF sensor to monitor the amount of air coming in, and using O2 sensor as a feedback to know the precise amount of fuel for perfect ratio.

Another clue to suggest that it is the O2 sensors that are the culprit is P0125 code that you have, as it is not about Temperature Sensor issue per say. This code indicates that something prevents the car from entering Closed Loop operation, and in that specific generation, it is usually the O2 sensors that cause it to appear, as they are the ones to fail more often that other components responsible for entering a Closed Loop operation, like MAF or Temperature sensors.

To see if my theory is in any way viable, here is a thread on how to diagnose O2 sensors, in short, check Engine Live Data, see if the O2 Sensor signal start to oscillate from about 0.2V to 0.8V as the engine warms up, if it doesn't, or the Sine wave that it's supposed to produce is shifted up or down, like if the signal oscillates from 0 to 0.5V for example, the sensor is bad and needs to be replaced.

Though not as informative, there is also a simpler way to see if it is the sensors that cause you issue - try unplugging both O2 sensors and going for a ride. CEL must come On right away, that's how you will know that the car no longer references O2 sensors. The car will not run perfect as O2 sensors are pretty vital for its operation, but if the things will improve, you will likely need new sensors.

Hope this helps and best of luck!

thraex

Thank you for your response!
Yes, I can do whatever it takes to further troubleshoot. The ECU has crossed my mind given the situation. Sorry if maybe my problem seems a bit vague and poorly described.

You mentioned fuel pressure regulator or filter? I'm wondering if these were bad, would the engine always run poorly or would it take a sensors reading to track these values?

My only traction with this issue has been the fact that it functions perfectly fine on an electrical reset. The idle, acceleration, and drive are all completely smooth. It almost appears as if the ECU starts using a sensor reading after the car is driven for a little bit, and then everything goes downhill.

This was probably worth mentioning initially, but before I changed my O2 sensors for the second time, I unplugged the sensors. (not removed, just unplugged) and the car was driving fine. The gas mileage was crap and the idle a little rough, but it put power to the wheels consistently.

Was wondering if theres no O2 sensors, does the ECU use some default values for fuel injection?

Thanks again for your help

thraex

Thank you for the reply! The part information really helps. My coils are NGK, I've heard they're on the better side of aftermarket but maybe not OEM specific. But what you're saying absolutely falls along my suspicions. I unplugged them before I put in my second set of O2 sensors and the car ran. Not well, but it ran. The thermostat and sensor are unlikely to be involved since theyre also both new and I get consistent readings. Right now I'm just an 18yr old college student and I havent been able to afford a real OBD-II scanner. I've been working off of codes, guesswork, the internet, and the feel/sound of the engine.

My next question would be what could be causing the O2 sensors to die so quickly. The first ones were cheap, so that adds up. The recent ones were Bosch and were not cheap, so I thought maybe they could do the job.

Could I be shorting them somehow? I have seafoam in the gas, could that foul them? I had just replaced them about a week ago and these issues are showing up again. I would hate to get new ones again only to kill them because of an underlying issue.

Thanks again for your help, really

Arsenii

What about the wires, which ones did you get?

Those would be the only aftermarket coils I would honestly consider, but nothing beats OEM in my opinion.

A solid scan tool is not as expensive as you may think nowadays, especially if you manage to get one used like I did back in the day. If you go new, look for something above about $50, as for used, just look for a name brand like Launch, Innova, Bosch, etc., mine was in basically new condition when I got it as the previous owner barely even used it, look locally on Craigslist and similar marketplaces.

Which model did you get? If those are generic sensors where you need to splice your own connector in, there is a chance you may have attached it incorrectly, or the sensor simply isn't suitable for your car, giving out a waveform that your car struggles to understand.

It also heavily depends on where you got them, places like eBay and Amazon are chock-full of counterfeit junk, it is very hard to find anything worth a second look there. I personally haven't used Bosch sensors in Toyota before, preferring to go with Denso where possible as it is an OEM manufacturer for Toyota, so again, it could be that those sensors are not compatible with your car, hard to tell without more information.

You can try contacting the place you got your sensors from, or Bosch themselves and ask if they are suitable for your specific car, and if so, ask them about the warranty and return policy they offer, there should be a way to get your money back if the sensors are indeed bad.

So long as you don't run the car straight off of Seafoam, it shouldn't affect much, so I doubt it's your problem. I haven't heard of ECU frying them either, as it is a sensor itself that produces voltage, not the ECU, and the Ground for the sensor goes to a completely different location.

Hope this helps and best of luck!

thraex

Thanks so much, your responses have been really helpful and I think i've narrowed the issue down to the Bank 2 sensor, right on the exhaust manifold.

I've tested the contacts with a multimeter and done some more research and now I'm wondering if my issue is that I'm using an O2 sensor instead of an A/F ratio sensor. I know they arent interchangable if the car calls for a wide band sensor, but I cant find anything specifying which one this specific year and model takes. Any resources you may know of or thoughts on what my next move should be?

Arsenii

Here you can learn more about Wide Band A/F sensors, with that, those cars didn't obtain them until 1999 with introduction of VVT-i system. In short, the difference is that an A/F sensor is a lot more precise, instead of blindly switching between Rich and Lean, such that there is no way for the ECU to tell How lean or How rich the mixture is, A/F sensor produces current that shows precisely what the condition of the mixture currently is, giving an ECU a much greater chance at precisely adjusting Air-Fuel mixture.

With that, O2 sensors also have two different types - Zirconium and Titanium, and they are not compatible. Zirconium sensor, which is installed in those cars by default, is the one to produce voltage with change of Oxygen level in the exhaust, while Titanium sensor changes its Resistance instead, requiring a Reference voltage to function, said voltage tends to differ quite a bit between manufacturers, Toyota tends to use 1V, while German manufacturers opt for 5V.

They both produce a Sine wave, and their readouts can look very similar, with Titanium sensors having a faster response to changes, while being very expensive, and not very durable. With that, they are not interchangeable, you cannot use Zirconium sensor in place of Titanium and vice-versa without some modifications, since again, one produces its own voltage, while the other only changes resistance, so both ECUs will have their own ways of interpreting data.

That is why it is important to know which specific model of the sensors you got, and whether they are even compatible with your car. Here is a Parts Catalogue for your car showing the correct Part Numbers for the reference, though you will have to find out whether your car is a California-spec with tighter emission regulations, there should be a sticker on the hood specifying the Emission System used in your car.

Hope this helps and best of luck!

thraex

I really appreciate your recent help. I changed out the bank 2 sensor to Denso and boom, P0125, P1150, and misfire codes disappeared. Awesome.

Now the car will enter closed loop fuel control. So the cars running nice and smooth open loop. Once the engine warms up and it enters closed loop the engine is running lean, throttle lag, little power, p0171. Sweet. lol

I appreciate your help with this issue, learned my lesson about these manufacturers. Ill be looking into a real scanner too.

Thanks again