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1999 Corolla Code P0171.

By Bad_dude, October 19, 2013

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Which one, and from where?


I bought the delphi one and from the your first link, the one that only take itunes gift cards. So far no order confirmation.


It looks like I lost the $31. No order update and no response from the company either.

You'll get it soon... If not tomorrow, next week for sure.


You'll get it soon... If not tomorrow, next week for sure.

You mean the order update or the order? default_smile



I really don't know if it's the aluminum intake manifold that is leaking at its seams or welds... It could be better inspected once removed if you replace its gasket... It could also be a vacuum leak at injector o-rings, or at a vacuum or PCV hose.

It appears to be an ongoing mystery for many with their 8th gen Corolla's, so I thought it could be something that is harder to find and easily overlooked... On the 9th gen Corolla with plastic intake manifold, it's always just the intake manifold gasket which has been revised.

How old is your upstream oxygen sensor, and does your engine burn a lot of oil?

Is it worse when colder outside? Have you replaced your IAT sensor?,carcode,1432911,parttype,5072

Delphi TS10029 (recommended)

Toyota # 89424-006010, or 89424-12010 (Denso).

Do you have the part number for the grommet that goes around this sensor in the air box?


Where exactly is your IAT sensor mounted?


It goes right into the air box side.

Can you post a photo of the grommet? Is it 1/2" inner diameter?


I don't need that grommet as it tight when I checked today. No word on my order yet. I guess I'll wait and see after another week to order another one. I check all of the connection and for cracks on the air filter housing. I spray some carb fluid around the engine to check for air leak again. Nothing. This is now a mystery for me. My wife took the car last week and the freaking mechanic replace the fuel rail and nothing changed. The new part though from the dealer doesn't seem to look perfectly like the old one on the car. I don't know what I could do next to get rid of the code. Bank 1 O2 sensor also was replaced with a Denso. What are the chances of having a defective O2 sensor when just replaced with new?

Thanks Dom.


It looks like I lost the money for the order. That website now gives me

Bandwidth Limit Exceeded

Just have the same code.


Just an update. We broke down and I asked my wife to take it to the local dealer. The first time they want $100 to diagnose. The 2nd time, we met a nice guy who recognized that the car belongs to a poor person. default_smile So he charges $50 for the thorough diagnostic, and a good cleaning. So their recommendation was replace all 4 fuel injectors and downstream O2 sensor. I already replaced the upstream, easy enough.

So here we are. I ordered OEM reman Denso injectors from Ebay for $75 per set. Bought the downstream O2 sensor from Rockauto, Denso also. So now I need help with these procedures.

1) Replacing the fuel injectors

2) Downstream O2 sensor.

Any DIYs for these two repairs?


I'm surprised that they came up with that diagnosis. But in your case, since it was so hard to diagnose, so intermittent - might be worth a shot to swap them out and see what happens.

The price you got on the reman Denso injectors is pretty decent - even if it turns out the original injectors are fine - you know that these are clean, flow well, and great to have extra injectors around for diagnostic purposes.

Can't beat Rockauto for prices on sensors.

Link that I've found for the injectors:

Downstream O2 sensor - lot easier to get to than the upstream one. The toughest part is getting to come loose, all that corrosion on it, might make it really tough to loosen up. Lots of PB Blaster or similar, heating it up, use the appropriate O2 sensor socket on it, or if you are dead set on replacing it - just cut the wiring off, use a deep well, 6-point socket on it. Wiring connector is under the front passenger seat, if I remember correctly - have to pull back the carpet some, hard to miss the connector.


The video doesn't work. Fish, what do you think the real culprit is?


The downstream O2 sensor is only a catalyst efficiency monitor. It has no effect on operating A/F ratio.

Sorry about the video - link must be dead / old link. Should be a similar one on Youtube - just search for 1ZZ-FE and fuel injector replacement - should be a couple on there.

As for the real culprit - for that particular code, unfortunately could be a number of things. Leaks in the induction, exhaust, and EVAP can cause that code to pop up. That means looking for potential vacuum leaks, poor fuel delivery, poor feedback control, etc. Most of them you've touched on here, except for replacing the injectors.

Given that you've looked under pretty much every other rock - might be worth a shot.


1) Where's the connector for the post Cat O2 sensor? How to get to it?

2) What's the torque specs for the fuel rail after I put the new injectors in?

3) Where do I find the fuse to kill the fuel pump so I could get rid of the gas already in the system to replace the injectors?


1) The connector for the post cat O2 sensor should be right behind the floor pan bump/reinforcement bar under the front passenger seat. Some have found it tucked under the carpeting - sometimes it pops out and is just laying there.

2) Torque on fuel rail - 14 ft.lbs

3) I think this has two components (can't remember for sure) - there is an EFI fuse under the hood + there is a fuel pump relay that is on the driver's side kick panel. Another option is to just disconnect the power leads to the fuel pump under the rear seats. Just pull up on the rear seat cushion, just clips holding it down - just disconnect the leads to the pump.


Just an update guys. I know everyone is anxious of how this was fixed. First off, I should have taken the car to the dealer. For $50-$100 diagnostic, that would have save me so much time, money, and headaches.

It was the fuel injectors. First when I just installed the injectors, I forgot to lube the o-rings and two got twisted and it was leaking gas like mad. I then lube them with dielectric grease, no more leak. The car was reset when I removed the battery to do the job. No more CEL. Now it failed smog twice after the fix already. First time my wife didn't drive the car enough like I told her to. Very impatient. Then the 2nd time, it was incomplete catalyst. The tech said it might be the CAT. I think she didn't heat the car up enough. No code for the catalyst. The post CAT O2 was replaced. So now she's using the car to go to work every day. Probably test again this weekend. Any suggestion on how to pass?

This car now consumes lots of oil. The dealer said the rear main seal is leaking. Nothing on the ground though. Right now I am running high mileage full Synthetic Mobile One. Should I switch to something else to reduce the consumption. The deal said this car is still in good shape even at 200K miles. It does not consume much oil. They said it's probably the leak.

What you guys think? They want $800 to do the job.

You'll have to see if the I/M readiness monitors get set to READY. Some OBD code readers will query the I/M readiness monitors and tell you if they are set or not.

There isn't really a "recipe" to try and speed up the process. It is just a sequence of cold start and cold soaks, average run time, average speed, ambient temperature, and a few more things. With my 2002 - it took me more than two weeks/~500 miles of my normal commuting to get the car to set the monitors.

As for oil - that stuff you have is pretty good. Only other one that I can think of is Valvoline Maxlife - tends to run a little thicker than Mobil 1 of the same viscosity rating.

Rear main leak is common when the mileage starts to run up there. I'd just keep running the higher mileage oil and clean that area off, see if the oil keeps leaking. Sometimes the valve cover / timing chain tensioner o-ring leaks, causing the oil to run down and make it look like a rear main leak. I'd clean the engine off as well as you can, and closely monitor where the leak is coming from. Valvecover and tensioner o-ring are way easier to change yourself and relatively cheap.

If it is the rear main - $800 is about the going price - lots of labor to get to it. Might be able to shop that around and find someone else that could do it for less. If you get lucky, the leak will stop or slow on its own.

Too bad we missed the injector O-rings before... I've mentioned possible vacuum leaks there in other threads, but you said it had no vacuum leaks. It can be obvious by just looking around them to see any evidence of leaking.


Too bad we missed the injector O-rings before... I've mentioned possible vacuum leaks there in other threads, but you said it had no vacuum leaks. It can be obvious by just looking around them to see any evidence of leaking.
Dom there's was no vaccuum leak until I tried to install the new injectors and then twisted the o-rings b/c of the lack of lube.




Took the car back in and didn't pass. Took the car and had the CAT replaced for $180 after marker. Took it back, pass instantly. So the car is ok for now. I am thinking about getting my wife another car as the car now consume oil too fast. It used to be one quart every oil change now it's one quart every week or two. Too much. If I use the higher viscosity grade would it slow it down? If so by how much?


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