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Discussion Starter #1
Trying to figure out why this 2019 z125 isn't running right. It started off running poorly after it got warmed up after it was ridden for a while, then it would run bad all the time. It would actually run decent at full throttle, but very bad at small throttle openings, especially under load like going up hills, sometimes it won't go at all.

So I thought maybe bad throttle position sensor, I unplugged it and the bike runs great it flys, but it won't idle with it unplugged. So I bought a new OEM throttle body with new throttle position and map sensors on eBay, installed that yesterday and for a little while it seemed like it was running good it definitely wasn't running very bad like before, but then it started running poorly again and again I unplugged the TPS sensor and it runs great again.

I also tried a oxygen sensor eliminater connector plug and that didn't help. I do have a few check engine light codes but that could just be from riding it with these sensors unplugged so I would need to do the 3 ride cycles procedure to clear the codes or see which ones remain after riding it three times. I have tried leaving the battery disconnected for a while a few times.

I don't know if maybe I need a new oxygen sensor, or somehow that throttle position sensor on the throttle body that I bought off eBay is no good, or if there is a way to test that?, Or what else the problem could be? Bad ecu?

Anyone have this problem? Thank you!
 

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Simple stuff first, is the air filter clean and is the gas fresh? Since it sounds like you've tried a bunch of stuff already maybe siphon the gas out and put in a fresh tank of premium. Check the spark plug. A semi fouled plug will cause these issues. Check the boot and plug wire as well. Make sure everything is connecting well.

What codes do you have?
A correctly built O2 eliminator will eliminate any O2 sensor issues. If you're not seeing an O2 code (33 and or 67) it's not that.

Attached is a snip from the service manual on how to test your TPS
 

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Discussion Starter #3
Thanks! The bike runs great, strong and smooth with the TPS sensor unplugged, so that should rule out just about everything except for the TPS sensor and the ECU and maybe the wiring. Also when it's running very bad at partial throttle openings with the TPS plugged in, it still runs fairly decent at full throttle

It has codes 11, 12, 13 and 67, but I was riding it with the sensors unplugged and haven't rode it enough yet to clear the codes. I'll test the TPS. Thanks
 

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when you replace the TB assy, you're supposed to perform a TPS calibration. its in the manual. You basically ground the test connector, hold throttle open, turn key on, wait 5 seconds, release throttle, wait 5 sec, turn key off, disconnect test connector from ground, then turn key on and wait 5 sec, turn off.
 

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Discussion Starter #5
Thanks alot I'll try that, I was wondering if it could be or needed to be recalibrated.
 

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oh ... 3 post while i was typing ..
Dont' see you saying you tried a TPS reset on old or did do it on new throttle body ?
Might have ran good unplugged because it gos into D-J mode (& a-N mode)
air intake & air temp on same plug also when you disconnected and gos into a-N mode but new throttle body should have fixed it if that was the problem ?
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You dont have Idle turned up do you (stunting)

Brad, any way this is a Limp Mode issue ?
 

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Discussion Starter #8
I tried the TPS calibration it didn't fix it. Sometimes when I was riding it tonight it would run smoothly until about half throttle and then run bad, and still run bad at full throttle. Other times it runs bad at small throttle openings but run half decent at full throttle. It doesn't stay consistent for very long. I was just going up a hill tonight and it all of a sudden started running much worse than it just was. I never did any actual TPS test or recalibrate the old tps. I still need to try to test the new one. I do think the calibration procedure was done correctly, the yellow light stopped blinking and remained on after part of the procedure like it says it will do in the manual, as pictured above. And I tried it 3 times.

Thanks alot for the help. I do think the ECU could be the problem. I see a get ECU on eBay I might have to buy and try out.
 

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Discussion Starter #9
I had a tps sensor for bad, it would run like crap, mine had a glitch, vibration would make the tps jump around, replaced it and it’s been good ever since
The bike does seem like it vibrates alot and makes noises because of the vibration.
 

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The bike does seem like it vibrates alot and makes noises because of the vibration.
Put a socket on the bottom rear motor mount bolt under the swing arm pivot bolt and make sure its really tight. Very common issue they come loose.
Have heard it causes shifting and jumping out of gear problems, but not any engine issues yet.
But maybe vibrating a sensor or connector so bad it could ?
Nothing wrong with it being a first :unsure:
 

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Discussion Starter #13
Yeah there's definitely a vibration issue and starting to think that could cause the sensors to go wacky. Also it usually revs very good and smooth in neutral or with the clutch in, but under load is when it often runs bad, but it does vibrate a lot and make the rattling noises when it is revved in neutral, like the exhaust is making noise from the vibration. Thanks
 

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Discussion Starter #15
It's all stock. I did check that engine mount bolt mentioned above, it wasn't loose but I did get it a tiny bit tighter, but didn't notice a difference afterwards, and all the other engine mount bolts were really tight. I can't tell exactly where it's vibrating but it does sound like the exhaust mostly making noise. Thanks
 

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Starting to think Exhaust Leak .
Easy to check. Cold start up block tail pipe exit with rag at for 3sec's (Max') long cycles and listen and feel for leak at header gasket to motor
A Loose or faulty exhaust gasket will produce an exhaust leak that will sound like a hissing or tapping sound coming from the engine. The sound may be especially pronounced during a cold start or during acceleration
Also Causes Excessive vibrations originating from the exhaust system
Exhaust leaks can throw off sensors, which may cause your engine to burn too much or not enough fuel.
Performance will change as motor warms up
Could have a bad CAT inside but i doubt it ?
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This is probably something really stupid easy and looking for one of the common issues isn't going to work :rolleyes:
.
 

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Discussion Starter #17
Thanks, I will check again. It does seem very likely the vibration made the throttle position and map sensor go bad. The bike ran good, I thought normal good, after I replaced the throttle body with sensors for about 20 minutes. Then the next time we rode it, it was running bad again, so maybe the vibration hurt the new sensors. I could get a like new exhaust on eBay to try. thanks!
 
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