Both MAF sensors read 0.39 to 0.40 gps engine off.
LTFT was -11.7 (engine off)
Downstream O2 voltage changing, other wonky readings
- Thread starter Jonas
- Start date
LTFT was -11.7 (engine off)
When your LTFT reaches it's "settle" point (-8.9% you said), I'm curious as to what your STFT is while at a steady cruise on flat ground. The engine needs to be loaded while taking this reading. If the STFT goes into the 7-9% positive rate, then your issue is only at idle. If it gets even MORE negative, you have either a fueling problem or an airflow reporting problem.
What brand of MAF sensors have you been using? Normally, I'm all for cheaper aftermarket parts however MAF's are one of those things I just won't skimp on. On your Vibe, it's Denso OE or nothing. There's also the possibility that your upstream O2 sensor is getting lazy. It is possible to disconnect the upstream O2, clear the memory, and then see where your STFT's are immediately after starting the engine. Do these tests with a warm engine. If the STFT sits around 0%, you've quite possibly found your issue. Lazy O2.
What brand of MAF sensors have you been using? Normally, I'm all for cheaper aftermarket parts however MAF's are one of those things I just won't skimp on. On your Vibe, it's Denso OE or nothing. There's also the possibility that your upstream O2 sensor is getting lazy. It is possible to disconnect the upstream O2, clear the memory, and then see where your STFT's are immediately after starting the engine. Do these tests with a warm engine. If the STFT sits around 0%, you've quite possibly found your issue. Lazy O2.
Both MAF sensors are Denso. The first replacement (with some bad reviews) was a Denso "first time fit." The one in my car now is the OEM MAF that says Toyota Denso on it-identical to the one that was in the car when I bought it.
I did a hard reboot on my car yesterday. I shorted the terminals together (had to pull out the battery so they would touch), turned the key on, and left it sis for about 20 minutes.
Now the car is acting more like it did when I first got it. Not only were the fuel trims around +/- 2 at idle the rest of the day, it idled up to about 1600 rpm every time I started it. Before it would only idle up a little when warm and then idle too low like it was going to stall, then level out. I'll keep an eye on it today and if it's still good, I'll assume it's good to go for a while.
The fluctuating downstream O2 sensor was a separate concern. I had read if the voltage fluctuates at idle after warmed up that indicates cat inefficiency. I thought maybe my cat was over-taxed from running too rich/lean lately, which is why I included that in the OP.
gathermewool
Site Donor 2023
Any mods?
None other than the aftermarket cat. The engine was rebuilt too if that matters.
I think your Vibe shares the same MAF sensor that my tC has. I should check, but my point is.. With the tc after I've cleaned the MAF with CRC's maf spray, I've always had to restart the computer/ecu to help it recognize the "clean" maf readings. I know that our ECU learns and stores that data that helps it behave in certain ways.
Before resetting it, it still behaves the way it did when it had a dirty MAF, well not completely, it's better but not a huge difference. Resetting the ecu by disconnecting the battery and letting it lose it's memory helps it re-learn when it's plugged back in. Then you really see a difference.
I'm wondering if that's the same thing that happened to your Vibe (since it's a toyota anyway) and now the "wonky" readings will be gone forever.. I'm betting it works properly from here on out.. until the maf needs to be cleaned again..
I think you're right. So far, it's running great. I've disconnected the negative terminal briefly before, but I think shorting the terminals and leaving it disconnected for longer is what it needed to really forget everything. It started idling up higher when I start it like a I mentioned before, but also the transmission was shifting funny for a little while too. It has since smoothed out and "learned " how I drive and now you can't feel it shift unless you're really paying attention. It still vibrates at low RPM, but feels more "reliable" for lack of a better word.I think your Vibe shares the same MAF sensor that my tC has. I should check, but my point is.. With the tc after I've cleaned the MAF with CRC's maf spray, I've always had to restart the computer/ecu to help it recognize the "clean" maf readings. I know that our ECU learns and stores that data that helps it behave in certain ways.
Before resetting it, it still behaves the way it did when it had a dirty MAF, well not completely, it's better but not a huge difference. Resetting the ecu by disconnecting the battery and letting it lose it's memory helps it re-learn when it's plugged back in. Then you really see a difference.
I'm wondering if that's the same thing that happened to your Vibe (since it's a toyota anyway) and now the "wonky" readings will be gone forever.. I'm betting it works properly from here on out.. until the maf needs to be cleaned again..
hey Jonas.. glad it's running well once you cleared the computer's memory. Yeah I have that on the tC too where the transmission shifts at odd points, then after awhile (about 100miles) it does smooth out, exactly like you're seeing.
the two things that caused vibration for me was a dirty throttle plate (used crc's maf sensor cleaner as it does not have acetone in it, that can melt the plastic intake manifold) and a bad rear engine mount. would be easy to see if your throttle plate/throat was gummed up. There is a hole on the back side of the throat that can be cleaned, that's the air port for the idle. I usually have someone turn the ignition key to on but not start the car, then have them push the gas pedal to open the throttle plate (electronic throttle) and clean that way. Hey something I had to say in case it could help solve your issues, which sounds exactly like my tC..
the two things that caused vibration for me was a dirty throttle plate (used crc's maf sensor cleaner as it does not have acetone in it, that can melt the plastic intake manifold) and a bad rear engine mount. would be easy to see if your throttle plate/throat was gummed up. There is a hole on the back side of the throat that can be cleaned, that's the air port for the idle. I usually have someone turn the ignition key to on but not start the car, then have them push the gas pedal to open the throttle plate (electronic throttle) and clean that way. Hey something I had to say in case it could help solve your issues, which sounds exactly like my tC..
Thanks. I cleaned the throttle plate best I could, but it's pretty hard to reach back there. The plate is perfectly shiny, but I can't see or get in there much further. I was able to reach in about an inch with a rag and got some black tar-like substance on it. It kinda makes sense because my vibration exists in and out of gear from 700 to 1000 rpm (worst around 900 rpm, throttle slightly open) and sometimes it's real bad, sometimes not so bad. I may remove the throttle body or at least try harder to get in there
ya I know of that "black tar".. odd that we have the same issues! What engine do you have in your 09 Vibe? Is it the 1.8 or the 2.4L? The tC has the 2.4L. but I know I share parts with the corolla/vibe and camry. The tC is just a parts bin mutt! lol..
back to the black tar. It was the same on mine and I did make sure to replace the pcv valve since the re-routing of those crankcase vapors goes directly into the throttle body. I'm thinking that might be the source of the black tar build up. Glad to hear you got it all shiny! Mine is all the way back by the firewall! You practically have to lay on the engine to get back there!
Might want to look at the engine mounts too. my rear one was bad, you could see it when it was up in the air, took the tire off to work on the brakes and I had my helper put their foot on the brake, shift into drive.. that's when I saw the rear mount bottom out! That was back in 2018, and mine is an 06.. so.. 12 years on mine and 12 years on your 09, brings you to the same time frame.. kinda makes sense with the timing.. But of course look into yours it may or not be bad.. just was the source of the rest of my vibrations.
But you're right, have to make sure the throttle body is completely clean before diagnosing/testing another theory like the engine mounts.. you're welcome by the way! I was just reading the post and thinking.. HEY! that sounds like what happens to my tC! gotta love the forums..
back to the black tar. It was the same on mine and I did make sure to replace the pcv valve since the re-routing of those crankcase vapors goes directly into the throttle body. I'm thinking that might be the source of the black tar build up. Glad to hear you got it all shiny! Mine is all the way back by the firewall! You practically have to lay on the engine to get back there!
Might want to look at the engine mounts too. my rear one was bad, you could see it when it was up in the air, took the tire off to work on the brakes and I had my helper put their foot on the brake, shift into drive.. that's when I saw the rear mount bottom out! That was back in 2018, and mine is an 06.. so.. 12 years on mine and 12 years on your 09, brings you to the same time frame.. kinda makes sense with the timing.. But of course look into yours it may or not be bad.. just was the source of the rest of my vibrations.
But you're right, have to make sure the throttle body is completely clean before diagnosing/testing another theory like the engine mounts.. you're welcome by the way! I was just reading the post and thinking.. HEY! that sounds like what happens to my tC! gotta love the forums..
*update* I needed a new air filter. The old one wasn't very dirty, but it was "shedding" a lot and the seal wasn't very good. I didn't notice until I installed a new filter and the air box clamps had resistance to them and clicked firmly in place. The new filter is a purolator one which has a rubber seal around the edge and the old Denso was like a cardboard type that was just sitting in there loose. The Denso would also stick to the top of the air box whenever I opened it. I got another lean code/maf code today and decided to try a new filter as a wild guess and it turned out to be just what I needed.
I've seen that with the genuine Toyota filter (not the denso aftermarket version).. It's the "Fuzzy" one I call it.. Over time it flattens its seal out, usually when it's time to change it. When new, the clips are really stiff to close. But glad you got it fixed! I'm wondering if any of that "shedding" got into the MAF sensor wires.. might be a source of your issues..
Bingo. I had also removed and re-inserted that filter a few times during it's life, so maybe that flattened out the seal some more? Denso aftermarket filters are highly regarded here, so maybe I'll try one in the future. I'm not terribly impressed with the "Toyota" Denso filter.
did you know there are two versions of the toyota filter from the dealer.. one that ends in 0D020 that's the factory one.. then there's a "value line" version that even in Toyota's brochure it says "not for warranty use".. wow that doesn't really inspire confidence! lol The value line part number ends in yzz03. But yeah I wouldn't be impressed with what's going on with yours either!
