Replaced both upstream 02 sensors - Toyota Nation Forum : Toyota Car and Truck Forums

R4lN · 01-31-2012, 05:41 PM

Hi, about a year ago one of my upstream 02 sensors went out. I was told I could just drive it on the other upstream if I didn't see any difference in gas mileage. I went ahead and did that. My van broke down finally about a week ago. I had it taken to a shop. He ran his tests on it and came back and told me that both upstream 02 sensors were bad. he proceeded to replace them. He used Bosch replacements. It works fine now except one problem. It seems to idle too low as compared to how it idled before. When I put the van in drive or reverse, it idles so low that the van kinda shakes a little. The power steering doesnt even feel "fluid" like its supposed to with the car idling this low. Its around 400rpm. Does anyone know what rmp its "supposed" to run at? My mechanic told me he flashed the computer 3x and finally ended up having to put a "generic" flash on the computer before it started running right. Honestly, i'm not sure how much of this I believe. Can anyone tell me what may be wrong with it and if its something as simple as turning up an idle screw? thanks in advance

It was running and idling perfectly fine before the breakdown and repair

R4lN · 02-01-2012, 08:17 PM

also noticed today that it wont start in the morning without you depressing the accelerator a little bit and holding it depressed with your foot on the break until it warms up a bit :/

TierOneSupplier · 02-02-2012, 09:01 PM

This doesn't sound normal. The van shouldn't break down if an o2 sensor fails. It would just stay in open loop, meaning engine managment parameters would be at factory defaults. Except for a slight decrease in MPG, you shouldn't have noticed any problems in driveability.

Some of the guys are going to chime in and say not to use Bosch o2 sensors on our vans, but the symptoms you're seeing sound like something besides a faulty o2 sensor.

A couple years ago, I went in after the knock sensor harness on our van, and upon putting everything back together, the engine idle was erractic for a couple of days. It's possible your low idle problem will correct itself after a day or two of driving. Your RPM at idle should be around 700 or 800 RPM (once the engine has been running a few minutes)

What exactly happened when your van broke down?

R4lN · 02-02-2012, 09:53 PM

well, here's what happened. a year ago one of the 02 sensors went out. I just drove it and didn't replace it. About a week ago we went to a night class at school. Turned the car off, and then came out after class, ( couple hours passed ) got in to start the car and it would not start. It was snowing that day so I didn't really get to check it out that well. It was freezing outside. I disconnected the airbox from the intake, I sprayed some starting fluid down in there and attempted to start the car. It wouldn't do anything but turn over. Every once in awhile, it would act like it was gonna try to fire but would continue to turn over really fast almost like it was free spinning. I thought it had jumped time to be honest. My mechanic went up there to get the van and he couldn't get it to start either UNTIL he depressed the gas pedal some. As soon as he did it, the car fired up but he had to hold the gas down when he came to a stop light to get it to continue to run. He drove the car home, ran his tests and came back to tell us that both upstream 02 sensors were bad. After he replaced them, apparently when he flashed the computer, he couldnt get it to idle right. He flashed it a second time with the same result. Then according to him, the third time he picked some "generic" flash off of his computer. The car runs perfect driving it down the road. Its just when you first start it in the morning, it doesnt seem to "choke" itself. You have to hold the pedal down to get it to start and then drive it down the road a little before it will run on its own. However, when you come to a stop sign or light, it drops down to 400 rpm at idle. I have also noticed that the when the car starts, it doesnt turn over the the same. It seems to really turn over fast.

I was actually dreading "thinking" about the problem being related to those bosch 02 sensors. I hope that has nothing to do with it. :/

One other thing, he told me that he pulled the threads out of the second bank in the exhaust manifold when he pulled out the old 02 sensor. He said he had to re-tap the hole. I don't know if this is true or not. I have the old 02 sensors and see no evidence of metal flashing anywhere within the grooves of the 02 threads. He had my van for too long and im not sure what he did that I believe and do not believe. Neverthaless, I hear no exhaust leak and that 02 sensor is staying in.

R4lN · 02-10-2012, 12:04 PM

I went ahead and drove the car for about 2 weeks and it seemed to pretty much repair itself. Everything is fine in terms of starting up in the morning. The idle smoothed out like its supposed to.. Everything is perfect except one thing. SOMETIMES, when you start the car it will revert back to idling at 450. Then if I kill the car and restart it, everything goes back to normal. Does anyone have a clue as to what this sounds like it could be? No check engine light or anything.