Rough idle, unbalanced fuel trims
09-12-20, 12:39 PM
#16
I'm not suggesting it's a bad MAF sensor. The connector is a multi-pin connector & if I remember correctly, it has either 5 or 7 electrical wires. If 1 or more of those connections is/are bad but not completely broken then you'll have an electrical intermittent. In turn, the ECU will receive the wrong signal(s) & adjust the LTFTs (Long Term Fuel Trims) on 1 or both banks accordingly.
09-12-20, 12:53 PM
#17
I've just looked at the MAF connector's pinouts & only 1 pin is designated a MAF signal output (pin 3) so if there's a bad connection there, it should affect the LTFTs on both banks but it's worth a try.
09-12-20, 08:14 PM
#18
Rookie
Thread Starter
I didn't inspect the other OCV. While it wouldn't be a bad idea to replace it, the fuel trims on that bank are good so there's no urgent need to.
So you already have tried to clean air mix passages.
Have you used a compressor to blow cloggings right after you sprayed the solvent?
If not yet, I recommend you to try that before you remove injectors. After I was taught so by MngreLMatt, I make it a rule to use a compressor. I find it more efficient and needs less solvent to clean passages.
Have you used a compressor to blow cloggings right after you sprayed the solvent?
If not yet, I recommend you to try that before you remove injectors. After I was taught so by MngreLMatt, I make it a rule to use a compressor. I find it more efficient and needs less solvent to clean passages.
What is condition of your COP (rubber) boots?
Experienced my first coil failure (1999)
The boots are removable and replaceable.
Inspected the junction of COP and metallic tube that extends inside boot to spark plug....
Definitely some resistance occuring there...and increase resistance may cause the spark to find another path.
.
Experienced my first coil failure (1999)
The boots are removable and replaceable.
Inspected the junction of COP and metallic tube that extends inside boot to spark plug....
Definitely some resistance occuring there...and increase resistance may cause the spark to find another path.
.
The symptoms definitely seem to point to a clogged air mix passage. If it isn't that, my next best guess would be a bad exhaust valve in the engine, but it runs so well under load and makes great smooth power so I doubt it. After that, I would guess it's some electrical gremlin, maybe a wiring, grounding or ECU problem in which case that is far above my pay grade to diagnose (aside from inspecting the ECU capacitors) and I don't know of any competent shops who are capable of advanced diagnostics of any kind. If anyone knows of any fine auto shops in MN however please do let me know. It would be nice to get this car running and driving the way it's supposed to.
Last edited by relentLS; 09-12-20 at 08:30 PM.
09-12-20, 08:58 PM
#19
Pole Position
Didn't know about that kit. Is the "SST" designed for cleaning the air mix passages?
I didn't inspect the other OCV. While it wouldn't be a bad idea to replace it, the fuel trims on that bank are good so there's no urgent need to.
I did not use compressed air as I don't have an air compressor. I ran the cleaner through each air passage with the engine running at about 1500 rpm.
Yes, since there's only one MAF sensor on this engine it shouldn't affect each bank individually but who knows, it's worth a try.
I replaced one coil on this engine. It failed catastrophically causing a complete misfire. Haven't touched the others. I don't think ignition related misfires generally cause negative fuel trims however, rather positive fuel trims, but I'm not sure. That would be a question for someone who is a diagnostics guru.
The symptoms definitely seem to point to a clogged air mix passage. If it isn't that, my next best guess would be a bad exhaust valve in the engine, but it runs so well under load and makes great smooth power so I doubt it. After that, I would guess it's some electrical gremlin, maybe a wiring, grounding or ECU problem in which case that is far above my pay grade to diagnose (aside from inspecting the ECU capacitors) and I don't know of any competent shops who are capable of advanced diagnostics of any kind. If anyone knows of any fine auto shops in MN however please do let me know. It would be nice to get this car running and driving the way it's supposed to.
I didn't inspect the other OCV. While it wouldn't be a bad idea to replace it, the fuel trims on that bank are good so there's no urgent need to.
I did not use compressed air as I don't have an air compressor. I ran the cleaner through each air passage with the engine running at about 1500 rpm.
Yes, since there's only one MAF sensor on this engine it shouldn't affect each bank individually but who knows, it's worth a try.
I replaced one coil on this engine. It failed catastrophically causing a complete misfire. Haven't touched the others. I don't think ignition related misfires generally cause negative fuel trims however, rather positive fuel trims, but I'm not sure. That would be a question for someone who is a diagnostics guru.
The symptoms definitely seem to point to a clogged air mix passage. If it isn't that, my next best guess would be a bad exhaust valve in the engine, but it runs so well under load and makes great smooth power so I doubt it. After that, I would guess it's some electrical gremlin, maybe a wiring, grounding or ECU problem in which case that is far above my pay grade to diagnose (aside from inspecting the ECU capacitors) and I don't know of any competent shops who are capable of advanced diagnostics of any kind. If anyone knows of any fine auto shops in MN however please do let me know. It would be nice to get this car running and driving the way it's supposed to.
09-12-20, 09:05 PM
#20
Rookie
Thread Starter
Well yes, it could be those too. Whatever it is, there's only so much I can do myself to diagnose it and I'd rather not just throw parts at it. It'd be nice to find a shop that actually knows how modern combustion engines work who could correctly diagnose and repair it. Then again, do any mechanics even know what the "air mix path" is? I thought "unfixable" cars were reserved for the Germans...it seems this car requires "relentless pursuit" to restore it back to it's intended operation.
Last edited by relentLS; 09-12-20 at 09:35 PM.
09-12-20, 11:54 PM
#21
How long has it been running under this condition? The reason it hasn't threw the error code(s) even though it's running rich is because the LTFT is only at -21% but once it reaches about -25% or more (or less depends how you interpret it), the ECU will no longer be able to compensate & make the adjustment. It'll set the code(s) then you can narrow down the issue from there so in this case, I suggest you to keep on driving it but keep an eye on the fuel trims & see if it's getting worse (keep the scanner hook up & monitor the fuel trims on real time). When you're facing emission control issues, it can be a lot of things so be patient & give it time then eventually, you'll find the root cause.
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relentLS (09-18-20)
09-13-20, 05:12 AM
#22
Pole Position
How long has it been running under this condition? The reason it hasn't threw the error code(s) even though it's running rich is because the LTFT is only at -21% but once it reaches about -25% or more (or less depends how you interpret it), the ECU will no longer be able to compensate & make the adjustment. It'll set the code(s) then you can narrow down the issue from there so in this case, I suggest you to keep on driving it but keep an eye on the fuel trims & see if it's getting worse (keep the scanner hook up & monitor the fuel trims on real time). When you're facing emission control issues, it can be a lot of things so be patient & give it time then eventually, you'll find the root cause.
It was apparent one cylinder was off..
While I suspected an ignition coil, wanted to conserve time trouble shooting.
So, instead of swapping out coils one at a time with spare, placed the transmission in drive, pressed the brake and held the accelerator to load the engine near (transmission).stall speed for several seconds.
On the third try, under this loading method, was able to promt the trouble light and acquired code for ignition coil cylinder 5.
Safety first:
No one or anything in front of vehicle...
Verify engine mounts are in good condition (Are yours original?) before doing so.
If no results, then take vehicle to Toyota/Lexus for proper diagnosis.
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relentLS (09-18-20)
01-28-21, 10:47 AM
#23
Rookie
Thread Starter
Finally Solved
The misfire ended up getting worse to the point where it threw a check engine light for cylinder #7 misfire. Coil and plug were good, compression was 190 psi, shop found the #7 fuel injector was bad. Replaced that injector and I had them clean out the air passages while they had the intake manifold off and now it runs beautifully. Also did the starter while they were in there.
Last edited by relentLS; 01-28-21 at 10:58 AM.
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BNastee (01-29-21)
01-30-21, 08:33 AM
#24
Pole Position
The misfire ended up getting worse to the point where it threw a check engine light for cylinder #7 misfire. Coil and plug were good, compression was 190 psi, shop found the #7 fuel injector was bad. Replaced that injector and I had them clean out the air passages while they had the intake manifold off and now it runs beautifully. Also did the starter while they were in there.
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relentLS (01-31-21)
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