- Thread starter
- #21
Alternator is new but I guess I could have it tested. As I mentioned this all started after a new alt was installed.
Rough Idle Help
- Thread starter SanDiegoCruiser
- Start date
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Can you just watch the voltage when it happens? Make sure its like 13.5+. Maybe you already have an accurate readout on a ham radio, scangauge, etc?
Maybe it is time to take it to someone that specialise in diagnostics, To be honest, a good technician should find this fairly easily as you can reproduce the fault, the hard ones to fix are the intermittent ones. Not all mechanics are the same, some know nothing about diagnostics and couldn't use test equipment as they don't know what the numbers mean, fault codes are just the start of the procedure of diagnostics, they certainly don't tell you all is good just because you don't have one. putting a vacuum gauge on or read your fuel trims will tell you more about how your engine is running, your fuel trims will compensate for any issues, so that is a good place to start, if the they are fine then it is likely that your engine itself is running good.
Always start at the battery, nothing works well with a bad battery, again these are what your technician should rule out straight away.
If it started after changing your alternator, then relearn your engine ECU by disconnecting your battery for 5 minutes, then leave to idle for 10 minutes with all equipment off. I am not 100% this is the correct procedure, but I use it and it seems to be good.
Another reason this issue shouldn't be hard to diagnose is that it can be reproduced at idle, not at highway speed. As you can use all test equipment and read the data whilst the vehicle is stationary and producing the fault.
I am not calling your mechanic a bad one, he might fix mechanical issues with ease, but to say he is stumped when the fault is right in front of you is a bit unprofessional, he just needs to admit he doesn't have the know how or equipment to get to the bottom of it and advise you to go elsewhere.
If this vehicle came to me, As you mentioned no CEL. I probably would of put a fuel pressure gauge, vacuum gauge and volt meter on before connecting the diagnostic machine as this information is harder to read from a machine. make sure the battery voltage is the same on techstream as you get directly across the battery as this could help you rule out a voltage drop.
Good luck though and hope you get it sorted.
Always start at the battery, nothing works well with a bad battery, again these are what your technician should rule out straight away.
If it started after changing your alternator, then relearn your engine ECU by disconnecting your battery for 5 minutes, then leave to idle for 10 minutes with all equipment off. I am not 100% this is the correct procedure, but I use it and it seems to be good.
Another reason this issue shouldn't be hard to diagnose is that it can be reproduced at idle, not at highway speed. As you can use all test equipment and read the data whilst the vehicle is stationary and producing the fault.
I am not calling your mechanic a bad one, he might fix mechanical issues with ease, but to say he is stumped when the fault is right in front of you is a bit unprofessional, he just needs to admit he doesn't have the know how or equipment to get to the bottom of it and advise you to go elsewhere.
If this vehicle came to me, As you mentioned no CEL. I probably would of put a fuel pressure gauge, vacuum gauge and volt meter on before connecting the diagnostic machine as this information is harder to read from a machine. make sure the battery voltage is the same on techstream as you get directly across the battery as this could help you rule out a voltage drop.
Good luck though and hope you get it sorted.
Ps, always use OEM parts on the engine, even spark plugs unless the others are tried and test and recommended from people on here. Don't trust a parts guy to give you compatible parts as they might fit but not quite work to spec. Alternators and battery also. Idle control differences work at such low voltages that the electro magnetic field from cheap coils and plugs can interfere with things.
- Thread starter
- #25
Did some tech stream analysis today. I don't understand much of this. Truck in drive not moving to simulate the issue.
Anyone see any issues? Looks like I have brake booster issues :-(
Anyone see any issues? Looks like I have brake booster issues :-(
Your 02 sensors look off to me, are your S1 sensors fluactuating up and down and your S2 sensor holding steady. Your B2S2 voltage looks low. Give your CATs a tap and see if they have broken up inside, This should bring up a fault code mind you.
- Thread starter
- #27
I'm still trying to tackle this issue. Been reading on the tundra forums that a bad engine coolant sensor can cause a rough idle. Anyone know where this is located on our 2UZ engines?
Edit: located here:100 - Serries coolant temperature sensor location
I've ordered this sensor. Hopefully it's the correct part
Delphi TS10198 Engine Coolant Temperature Sensor https://www.amazon.com/dp/B000CGI9B4/ref=cm_sw_r_cp_tai_U3T4zbX068G0R
Edit: located here:100 - Serries coolant temperature sensor location
I've ordered this sensor. Hopefully it's the correct part
Delphi TS10198 Engine Coolant Temperature Sensor https://www.amazon.com/dp/B000CGI9B4/ref=cm_sw_r_cp_tai_U3T4zbX068G0R
if I saw that short term fuel trim number @ 3.8, at hot idle, just sitting there, I would do some more checking. You have to really manipulate the pedal to get high numbers like that. I'd check at idle again with a battery reset, and at say 1500 rpm. Julien's advice is always right on. Depending on more readings there is definitely something going on with 02 voltages and, in my opinion, fuel trim.
- Thread starter
- #29
Other than 02 sensors, would this point to a potential bad Cat?
2001LC
SILVER Star
The "D" vibration has be covered extensively in mud. For my 01 (after extensive messing with) I found one thing that made a big difference. This is to disconnect battery for 20 minutes or more, while doing a minor tune up. Vibration and shake at Idle see post #84. remember to always clean & grease battery post to finish up. I do this every fall as fuel blend changes at the gas stations. Make sure to check all vacuum lines including PCV valve, grommet and hoses. Two others vacuum hoses often missed, are coming off the power steering van pump.
With your tech stream, if the simple tune doesn't do the trick. I'd then look to Fuel Injector.
When to replace fuel injectors
Also check your positive and negative connections through engine compartment. See big three The Big 3 Wiring Upgrade
I just learned some new stuff i posted in #44 "The Big Three" Electrical Upgrade
Coils are also suspect and worth a second look. Heat is the enemy here, and wide gap of spark plugs will create more of it. Not a real test but look for coils that show signs of heat like discolored or rubber of boot cracking, it's only clues not conclusive.
When to replace Ignition coils.
The least common is a cracked flex plate. IIRC this can be inspected from below by removing inspection cover off the bell housing.
With your tech stream, if the simple tune doesn't do the trick. I'd then look to Fuel Injector.
When to replace fuel injectors
Also check your positive and negative connections through engine compartment. See big three The Big 3 Wiring Upgrade
I just learned some new stuff i posted in #44 "The Big Three" Electrical Upgrade
Coils are also suspect and worth a second look. Heat is the enemy here, and wide gap of spark plugs will create more of it. Not a real test but look for coils that show signs of heat like discolored or rubber of boot cracking, it's only clues not conclusive.
When to replace Ignition coils.
The least common is a cracked flex plate. IIRC this can be inspected from below by removing inspection cover off the bell housing.
My D vibration was due to CATs, it was never to bad but I always drop to neutral in stopped traffic. Mine failed what you call a Smog test(MOT over here) so checked my 02 voltages, my downstream sensors where switching so I knew my CATS where bad. The reason I think the CEL didn't illuminate is because the Emmision laws over here didn't need the CAT efficiency monitored until 2005.
There are three reasons which could explain my vibration improvement after replacement , one is that someone had put aftermarket CATS on and that they where a bottleneck, two is that they where a slightly different shape and where putting pressure on the mounting points and three is that they where a lot thinner and lighter so resonance came into play.
After replacement Idle is quieter, no hum in the background. The truck drives as if it is lighter so more throttle responsive. Vibration hum at 60mph is also gone.
I always knew I had slight resonance in the down pipes but never looked into it as I wasn't prepared to spend time and money on something that didn't really bother me, plus they are the CATs which are pretty expensive so until they failed It wasn't going to bother me. When I removed the CATs there where not broken up, they just had a white powdered look to them so in the trash they went.
To your truck, your B2S2 reading is low, is this fluctuating or a steady low, try driving it to make sure the CATs are nice and hot before taking these readings.
Also your LTFT are a negative number, not by much but it is less common than a positive. check your air filter. A negative number is less common as it means less oxygen is getting to your 02, so to much fuel or not enough air flow. A bad CAT could cause less air flow, but you might want to consider doing a compression check and if you can get your hands on a Vacuum Gauge this would give you a good indication to what is going on. A bad CAT won't cause any issue unless it is a blockage(bottleneck).
There are three reasons which could explain my vibration improvement after replacement , one is that someone had put aftermarket CATS on and that they where a bottleneck, two is that they where a slightly different shape and where putting pressure on the mounting points and three is that they where a lot thinner and lighter so resonance came into play.
After replacement Idle is quieter, no hum in the background. The truck drives as if it is lighter so more throttle responsive. Vibration hum at 60mph is also gone.
I always knew I had slight resonance in the down pipes but never looked into it as I wasn't prepared to spend time and money on something that didn't really bother me, plus they are the CATs which are pretty expensive so until they failed It wasn't going to bother me. When I removed the CATs there where not broken up, they just had a white powdered look to them so in the trash they went.
To your truck, your B2S2 reading is low, is this fluctuating or a steady low, try driving it to make sure the CATs are nice and hot before taking these readings.
Also your LTFT are a negative number, not by much but it is less common than a positive. check your air filter. A negative number is less common as it means less oxygen is getting to your 02, so to much fuel or not enough air flow. A bad CAT could cause less air flow, but you might want to consider doing a compression check and if you can get your hands on a Vacuum Gauge this would give you a good indication to what is going on. A bad CAT won't cause any issue unless it is a blockage(bottleneck).
2001LC
SILVER Star
To @Julian Stead point of possible cat issue.
Cats can also be improved somewhat with and off the shelve additive cleaner added to gas tank. You can also run at high RPM (above 4,500 RPM while in low gears works well) for 10 minutes rest at normal driving RPM 10 minutes and repeat. Just make sure you've got good oil in the engine. This is like turning on your household oven to clean. It heats the cats cooking off gunk, or so the theory goes.
Cats can also be improved somewhat with and off the shelve additive cleaner added to gas tank. You can also run at high RPM (above 4,500 RPM while in low gears works well) for 10 minutes rest at normal driving RPM 10 minutes and repeat. Just make sure you've got good oil in the engine. This is like turning on your household oven to clean. It heats the cats cooking off gunk, or so the theory goes.
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I drove 80 miles with Cataclean additive in with OD switched off for higher revs. It didn't make a difference. My thought was how much precious metals could be in a cheap $200 aftermarket CAT to begin with.
2001LC
SILVER Star
Did i missing something. Does OP have aftermarket CATs also.
I've edited my "CAT cooking off" post to read above 4,500 RPM. It's kind of scary running engine near 5K RPM for very long. I get scared I'll throw a rod or float the valves, but I never have. I've done this in 300K mile rigs, with poor oil in & history of changes.
To achieve this locally I must gear down, as top speed limit is 75 MPH around here. Sometime I'll do blow out on city streets, but low speed doesn't produce much air flow to cool radiator, so I only do for few minutes like when using Sea-foam fog treatment.
This cooking off is something I read about in last few years, it made sense to me. I' drive with lite foot general. But now and then I'll floor it getting on HWY, to blow out the carbon. This has been a practice of mine for many years, as is driving on HWY all I can. Driving around town on short trips are hard on most any car. Blowing out seem to help. I do extra blowing out whenever I've a can of 44K in the tank also.
I've edited my "CAT cooking off" post to read above 4,500 RPM. It's kind of scary running engine near 5K RPM for very long. I get scared I'll throw a rod or float the valves, but I never have. I've done this in 300K mile rigs, with poor oil in & history of changes.
To achieve this locally I must gear down, as top speed limit is 75 MPH around here. Sometime I'll do blow out on city streets, but low speed doesn't produce much air flow to cool radiator, so I only do for few minutes like when using Sea-foam fog treatment.
This cooking off is something I read about in last few years, it made sense to me. I' drive with lite foot general. But now and then I'll floor it getting on HWY, to blow out the carbon. This has been a practice of mine for many years, as is driving on HWY all I can. Driving around town on short trips are hard on most any car. Blowing out seem to help. I do extra blowing out whenever I've a can of 44K in the tank also.
No sorry, it was just my experience.
Got to agree you can salvage a less than efficient CAT with a good quality fuel additive and a blast on the Hwy. It is what a lot of MOT stations over here tell you to do if it fails on emmisions.
No, In my LC it would point to an injector that wasn't connected or coil or fpr, or fuel pump. BUT, I prefer working from front to rear on front engine cars, and I'm further along in mine as far as fuel system check/replacement goes.
I will always believe that air, fuel and spark delivery trump all at the first go around. If you can't verify that then what have you? I'm a novice at nippondenso compared to bosch dme.
- Thread starter
- #38
To follow up on this post. I think I finally figured it out! Bad MAF sensor. Ordered a Denso replacement from Amazon and popped it in. Seems like it it fixed 99% of the issue! Remember, no codes were thrown, so that’s why this was never replaced.
I’ll do some more testing over the next week, but so far no more rough idle. What made me go for this fix was on a recent trip up at 8K feet elevation the idle was perfect! This made me start thinking about the various sensors etc.
I’ll do some more testing over the next week, but so far no more rough idle. What made me go for this fix was on a recent trip up at 8K feet elevation the idle was perfect! This made me start thinking about the various sensors etc.
94SRUNNER
GOLD Star
Thanks for following up. Glad you figured it out!
check your coils under LOAD!!!!!
put in gear hold brake 2500 rpm
disconnect coils one at time when u find one that has no effect on eng sound rpm thats the bad coil!!!!! at idle this will not identify bad coil!!! took me 2 weeks to figure this problem out!!! unplug maf so runs with airbox off...
