Rough idle, unbalanced fuel trims
09-01-20, 02:13 PM
#1
Rookie
Thread Starter
Rough idle, unbalanced fuel trims
I have a ‘98 LS with 127,000 mi. It runs on 7 cylinders at idle but feels smooth under load.
Bank 1 fuel trims are negative at -21% at idle but they normalize under a little throttle to within -10%-0%. Bank 2 fuel trims look good.
I had it at a shop but as usual they couldn’t find anything wrong other than possibly a bad oxygen sensor.
I replaced the bank 1 pre-catalyst sensor and it didn’t fix it. Also tried a fuel induction service which helped but didn’t fix it either.
I’m thinking it’s the bank 1 VVTI solenoid, an electrical issue like the ECU (but why would that only affect one bank...), a faulty fuel injector or a cylinder head valve problem.
If anyone has had a similar experience with one side of the engine not running right I would appreciate hearing your experience and how you solved it.
Seems like competent shops that are willing and able to diagnose these issues are rare these days. I’d like to be able to balance a coin on the engine while it’s idling.
Bank 1 fuel trims are negative at -21% at idle but they normalize under a little throttle to within -10%-0%. Bank 2 fuel trims look good.
I had it at a shop but as usual they couldn’t find anything wrong other than possibly a bad oxygen sensor.
I replaced the bank 1 pre-catalyst sensor and it didn’t fix it. Also tried a fuel induction service which helped but didn’t fix it either.
I’m thinking it’s the bank 1 VVTI solenoid, an electrical issue like the ECU (but why would that only affect one bank...), a faulty fuel injector or a cylinder head valve problem.
If anyone has had a similar experience with one side of the engine not running right I would appreciate hearing your experience and how you solved it.
Seems like competent shops that are willing and able to diagnose these issues are rare these days. I’d like to be able to balance a coin on the engine while it’s idling.
Last edited by relentLS; 09-01-20 at 03:16 PM.
09-01-20, 05:27 PM
#2
So it's just one cylinder not working right on bank 1 on idle? Did you manually take off one spark plug wire / disconnect the connections one at a time to figure out which one it is while it's idling?
When you find the right cylinder that is not working right it will run the same at idle when you disconnect it.
If you disconnect one of the connections and it is running the differently at idle, that is not the one that's the problem.
Shouldn't be a cylinder head / valve problem with the miles on the car as it is. I wouldn't dive into it too deep with more complex issues until you isolate which cylinder it is then trouble shoot it after that with the more common simpler fixes.
When you find the right cylinder that is not working right it will run the same at idle when you disconnect it.
If you disconnect one of the connections and it is running the differently at idle, that is not the one that's the problem.
Shouldn't be a cylinder head / valve problem with the miles on the car as it is. I wouldn't dive into it too deep with more complex issues until you isolate which cylinder it is then trouble shoot it after that with the more common simpler fixes.
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relentLS (09-03-20)
09-01-20, 05:52 PM
#3
Pole Position
I have a ‘98 LS with 127,000 mi. It runs on 7 cylinders at idle but feels smooth under load.
Bank 1 fuel trims are negative at -21% at idle but they normalize under a little throttle to within -10%-0%. Bank 2 fuel trims look good.
I had it at a shop but as usual they couldn’t find anything wrong other than possibly a bad oxygen sensor.
I replaced the bank 1 pre-catalyst sensor and it didn’t fix it. Also tried a fuel induction service which helped but didn’t fix it either.
I’m thinking it’s the bank 1 VVTI solenoid, an electrical issue like the ECU (but why would that only affect one bank...), a faulty fuel injector or a cylinder head valve problem.
If anyone has had a similar experience with one side of the engine not running right I would appreciate hearing your experience and how you solved it.
Seems like competent shops that are willing and able to diagnose these issues are rare these days. I’d like to be able to balance a coin on the engine while it’s idling.
Bank 1 fuel trims are negative at -21% at idle but they normalize under a little throttle to within -10%-0%. Bank 2 fuel trims look good.
I had it at a shop but as usual they couldn’t find anything wrong other than possibly a bad oxygen sensor.
I replaced the bank 1 pre-catalyst sensor and it didn’t fix it. Also tried a fuel induction service which helped but didn’t fix it either.
I’m thinking it’s the bank 1 VVTI solenoid, an electrical issue like the ECU (but why would that only affect one bank...), a faulty fuel injector or a cylinder head valve problem.
If anyone has had a similar experience with one side of the engine not running right I would appreciate hearing your experience and how you solved it.
Seems like competent shops that are willing and able to diagnose these issues are rare these days. I’d like to be able to balance a coin on the engine while it’s idling.
Check:
Spark plug tubes for oil.
Coil on plug ignitors and connections.
Fuel injector connectors.
Oil Contol Valves (remove and if either OCV rattles when you shake them, then defective)
PCV valve and hoses
Vacuum hoses.
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relentLS (09-03-20)
09-03-20, 11:15 AM
#4
Rookie
Thread Starter
Got a chance to look at it today. I forgot to mention, there are no trouble codes. Valve cover gaskets and spark plug tube seals are new. The ignition coil and fuel injector connections look good. PCV valve and hose are new and there are no vacuum leaks. Didn't get a chance to try the cylinder balance test yet as it is a somewhat intermittent misfire.
However, I removed the bank 1 OCV and there is indeed a slight rattle when shaken. Think I might try replacing both of them, hopefully that is the issue.
However, I removed the bank 1 OCV and there is indeed a slight rattle when shaken. Think I might try replacing both of them, hopefully that is the issue.
09-03-20, 02:01 PM
#5
Pole Position
Got a chance to look at it today. I forgot to mention, there are no trouble codes. Valve cover gaskets and spark plug tube seals are new. The ignition coil and fuel injector connections look good. PCV valve and hose are new and there are no vacuum leaks. Didn't get a chance to try the cylinder balance test yet as it is a somewhat intermittent misfire.
However, I removed the bank 1 OCV and there is indeed a slight rattle when shaken. Think I might try replacing both of them, hopefully that is the issue.
However, I removed the bank 1 OCV and there is indeed a slight rattle when shaken. Think I might try replacing both of them, hopefully that is the issue.
Sounds like you found the problem.
Now, when you go to the dealer (Don't use aftermarket), they have a made in Mexico and made in Japan P.N.
Guess which OCV is more durable?
09-03-20, 02:11 PM
#6
Rookie
Thread Starter
Dang, I already ordered the part from Lexus Parts Now. They listed 2 parts: #15340-50010, and an updated part with #15340-0F010. Of course I went with the "updated" part. Let me guess, that's the one made in Mexico...
09-03-20, 02:15 PM
#7
Lexus Fanatic
15340-0F010 supersedes 15340-50010 only way to get 15340-50010 is find new-old stock.
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09-11-20, 02:41 PM
#8
Rookie
Thread Starter
I replaced the Bank 1 OCV and reset the ECU. No change, still have the rough idle and negative fuel trims. I also had a listen to the fuel injectors and they sounded quite good.
This is looking more like an exhaust valve problem. I think one of them isn't sealing fully but it's not bad enough to cause a complete misfire and set a rich code. I guess a compression test would be needed. I hope I'm wrong though.
I suppose it could be EGR, fuel pressure or ECU related as well.
This is looking more like an exhaust valve problem. I think one of them isn't sealing fully but it's not bad enough to cause a complete misfire and set a rich code. I guess a compression test would be needed. I hope I'm wrong though.
I suppose it could be EGR, fuel pressure or ECU related as well.
Last edited by relentLS; 09-11-20 at 05:07 PM.
09-11-20, 05:08 PM
#9
Moderator
https://www.clublexus.com/forums/ls-...ml#post8906844
09-11-20, 05:35 PM
#10
Rookie
Thread Starter
Those your symptoms remind me of a blocked air mix passage of an injector or the passage to injectors. It often causes a single bank fuel trim problem only at a lower rpm situation (idle and a bit higher rpm). I'd simply try cleaning the passage first before I tackle the valve. Hope the post below might help you some.
https://www.clublexus.com/forums/ls-...ml#post8906844
https://www.clublexus.com/forums/ls-...ml#post8906844
Maybe I need to remove the injectors and clean the passages. I can see how those tiny air passages could easily get clogged.
09-11-20, 06:41 PM
#11
Moderator
I actually already tried cleaning the air mix paths. I used 1 can of Seafoam per side with no improvement. Then I tried B12 Chemtool spray but it got my cats too hot so I stopped. I also took it to the dealer for a fuel induction service. However the symptoms you describe are exactly what I'm experiencing.
Maybe I need to remove the injectors and clean the passages. I can see how those tiny air passages could easily get clogged.
Maybe I need to remove the injectors and clean the passages. I can see how those tiny air passages could easily get clogged.
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.
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BNastee (01-29-21)
09-11-20, 07:34 PM
#12
Pole Position
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.
Toyota offers a kit for what ails you. The SST depicted is required. (~$60 extra)
It is interesting your OCV rattles (which is indicative of failure), yet replacement did not resolve the issue.
Did you inspect opposing OCV?
Last edited by YODAONE; 09-11-20 at 07:49 PM.
09-11-20, 08:53 PM
#13
I had a very similar problem w/ the rich fuel trim condition & it took me a long time to find out the root cause. The problem turned out to be a bad (intermittent) MAF connector so here's what you should try: Hookup the OBDII scanner then start the car & let it warms up to operating temperature then look at the fuel trims on both banks in real time. While watching the fuel trims, wiggle the wires on the connector. You can also wiggle the connector and/or put some pressure on it to simulate a good mating. It'll take 30 sec or so for the fuel trims to change/go back to normal. If the fuel trims do go back to normal then you owe me dinner. Best of luck.
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BNastee (01-29-21)
09-12-20, 07:17 AM
#14
I had a very similar problem w/ the rich fuel trim condition & it took me a long time to find out the root cause. The problem turned out to be a bad (intermittent) MAF connector so here's what you should try: Hookup the OBDII scanner then start the car & let it warms up to operating temperature then look at the fuel trims on both banks in real time. While watching the fuel trims, wiggle the wires on the connector. You can also wiggle the connector and/or put some pressure on it to simulate a good mating. It'll take 30 sec or so for the fuel trims to change/go back to normal. If the fuel trims do go back to normal then you owe me dinner. Best of luck.
09-12-20, 09:16 AM
#15
Pole Position
I have a ‘98 LS with 127,000 mi. It runs on 7 cylinders at idle but feels smooth under load.
Bank 1 fuel trims are negative at -21% at idle but they normalize under a little throttle to within -10%-0%. Bank 2 fuel trims look good.
I had it at a shop but as usual they couldn’t find anything wrong other than possibly a bad oxygen sensor.
I replaced the bank 1 pre-catalyst sensor and it didn’t fix it. Also tried a fuel induction service which helped but didn’t fix it either.
I’m thinking it’s the bank 1 VVTI solenoid, an electrical issue like the ECU (but why would that only affect one bank...), a faulty fuel injector or a cylinder head valve problem.
If anyone has had a similar experience with one side of the engine not running right I would appreciate hearing your experience and how you solved it.
Seems like competent shops that are willing and able to diagnose these issues are rare these days. I’d like to be able to balance a coin on the engine while it’s idling.
Bank 1 fuel trims are negative at -21% at idle but they normalize under a little throttle to within -10%-0%. Bank 2 fuel trims look good.
I had it at a shop but as usual they couldn’t find anything wrong other than possibly a bad oxygen sensor.
I replaced the bank 1 pre-catalyst sensor and it didn’t fix it. Also tried a fuel induction service which helped but didn’t fix it either.
I’m thinking it’s the bank 1 VVTI solenoid, an electrical issue like the ECU (but why would that only affect one bank...), a faulty fuel injector or a cylinder head valve problem.
If anyone has had a similar experience with one side of the engine not running right I would appreciate hearing your experience and how you solved it.
Seems like competent shops that are willing and able to diagnose these issues are rare these days. I’d like to be able to balance a coin on the engine while it’s idling.
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.
.