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Discussion Starter · #1 ·
Let me start off with saying, Hi! My name is Jeremy, and I live in Ocala, FL. Ive been in and around the Automotive field my entire life (literally), and hope to contribute at least as much to the forum, as I've gotten (through lurking, lol)

Ive done all the searching I can, as well as tons & mega-tons of diag work, and cant figure this one out. Rough Idle on cold start up (about 50% of the time), within minutes, it runs great. Intermittently, it will begin to stumble/shutter at low RPMS/Idle. Whether it is in gear or not has no bearing. Even drove it around for 2 days with the scanner connected, hoping to see a sensor hiccup. It does NOT have any codes, Pending or otherwise, and everything in the data stream appears good(temp snsr, MAF Snsr, misfire monitor, etc).

It is a 2002 Tundra Limited, Access Cab, 2wd, Automatic, 4.7L V8- 226,xxx miles

Things Done-(in no particular order)
Throttle Body & Gasket (First cleaned TB, then replaced)
Denso Iridium Plugs (it needed them anyway)
1 Coil Pack (Didn't like the resistance values on it, so I replaced it)
Mass Airflow Sensor (Cleaned first, no change, then replaced, still no change)
Oxygen Sensors (All 4- At one time it was setting codes for the 2 that commonly go bad, replaced all 4 anyway)

Edit:I forgot to mention I also sprayed the intake down with carb cleaner both when the stumble was happening, and when it was not. There was no difference in the way it ran, nor any changes to Oxygen Snsr readings

Later this evening I am replacing the fuel filter, because it has been about a year since last replacement. I find it incredibly unlikely that this will help with the problem, but the preventative maintenance must soldier on!

Thanks in Advance :D
 

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Hello Jeremy, and welcome to Tundra Solutions!

Maybe the problem is electrical?
Have you checked and cleaned your ground connections under the hood?
I have seen bad grounds that get "better" with heat and vibration, then get "worse" when they sit and get cold.

Something else cheap and easy to try if you haven't.

Was your replacement coil a Denso unit?
Also, many on here recommend the standard Denso K20R-U spark plug over the iridium for the older non-vvt engines.

Jim
 

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Discussion Starter · #3 ·
Thanks for the welcome!

It may well be a ground, I may have missed some, although Ive never personally seen a ground do this sort of weirdness. I cleaned off a couple that I saw, just for general purpose and to rule them out, but I know there are more under there.

Surprisingly yes, the coil was a denso. It was from one of the various parts houses we use (cant remember which one TBH, thats not my job. I fix stuff, not order stuff lol), but when I opened the box, it was a denso coil in the toyota labeled parts bag. As for the plugs, if they were the issue, there wouldve been some change between when the old ones were in it, and then when I switched to t he new ones. The only differences were that the gas mileage increased greatly, and the truck has more power.

This is driving me nuts......


Jeremy
 

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Do the V8s have an idle air control valve? If so, might that cause these symptoms? I cleaned mine recently (v6) while troubleshooting a starting hiccup I was having after truck was warmed up. These get LOTS of carbon buildup.
 

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Discussion Starter · #7 ·
Coolant sensor reads properly, and resistance is good. MAF replaced (no change, readings are proper). If there IS a vacuum leak, its gotta be somewhere that I can't get sprayed down with Carb cleaner. The IAC (or whatever its called on this stupid million dollar throttle body) is, For all intents and purposes, new. Have tried alternate gas stations for fill ups, and no change. Added some Dry Gas, no change, added Octane booster, no change. Ran a tank of premium, no change ( except for the very tiny ping it had at close to the red line being gone). Gonna have to try and figure out how to get a fuel pressure gauge on this sucker.... cant remember if I saw a fuel pressure test fitting on it....:confused:
 

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Discussion Starter · #9 ·
Yes, it has a new air filter (well, new-ish. It was replaced 1 month ago) and it's not a K&N. Fuel pressure is looking ok FYI... .but then again, it has only acted up once over the weekend, and not while I had the damn gauge on it.... :beatsme:
 

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My next guess is that the timing is off. Have you redone the timing belt recently, and if so, did you use the appropriate timing mark?

(When I changed my timing belt the first time, I paid a mechanic. He lined the timing belt up to the "T," but that's not the timing mark actually. The correct timing mark is a line next to the "T.")

My truck wouldn't idle for quite some time, but once I redid the timing belt, it idled perfectly.
 

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Discussion Starter · #11 ·
Timing belt has been on it for just over a year, been fine till last month. And the problem its having is relatively intermittent..... HOWEVER... a slight change to the frequency now.... When its cold (been sitting over night, or for a few hours) it does it for about 10 seconds, and then is fine all the way till it warms up. Then, when sitting at idle for an extended period of time (10-15mins) it will begin to get rough again. aND THEN it could either smooth right out after driving it, or once in a while it doesnt lol ...
 

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And it never shuts off while it's idling poorly?

When you changed the spark plugs, did you put on right-side up the round rubber gaskets (?) that seal the coils to the heads? I ask because the last time I changed my plugs, the passenger side gaskets were put on upside down, so eventually it led to a misfiring of sorts. I bought new plugs and installed them, at which time I noticed my screw up. I no longer have that misfire.

Also, there has to be some sort of sensor that is regulating air flow or idle control. Maybe that sensor has gone bad.
 

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I am having the identical problem right now. 3 months ago I rebuilt another engine to drop in and it seemed to be running great and strong. Over the past couple days, I have noticed very similar issues as you Ozone5576. Tonight I found a loose connector on number 6 injector, clipped it in fully, but it still seems to be having the intermittent miss. Mine also is mostly at idle and in gear. If I powerbrake it, she does it a little more. When cold, it is not as noticeable but really shows quite quickly when warm. If you find something that helps please post it up! I am going to keep digging into mine in hopes that I can figure something out. It is really annoying!
 

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Discussion Starter · #14 ·
@aetuned - Yes it IS annoying.... difference with my problem is, that when I power brake it even a little, it smooths right out.... like nothing is happening.
@Antipas- I was thinking something similar, at least in that line of thinking anyway. gaskets installed as intended, and i dunno about whatever sensor/idle control, as the PITA wont do it when I h ave a scanner handy, but at all other times Ive had it, everything looked great :confused:
 

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@Ozone5576 - I must have missed that while reading through. I made progress on mine today though. I had a buddy hookup his SOLUS scanner and I watched the active misfire counters while running in the conditions I noticed the most roughness. Found that #7 cylinder was the only cylinder getting misfire counts. I swapped the coil to #5 cylinder and the misfire followed it. I am going to throw in a new coil tonight and recheck but I'm 99.9% sure this is my problem. I hope this helps! Keep updated on your findings as well!
 

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Discussion Starter · #17 ·
@Ozone5576 - I must have missed that while reading through. I made progress on mine today though. I had a buddy hookup his SOLUS scanner and I watched the active misfire counters while running in the conditions I noticed the most roughness. Found that #7 cylinder was the only cylinder getting misfire counts. I swapped the coil to #5 cylinder and the misfire followed it. I am going to throw in a new coil tonight and recheck but I'm 99.9% sure this is my problem. I hope this helps! Keep updated on your findings as well!
No worries :D. I hooked up my MODIS and previously saw similar misfire issues, but on CYl #4. Replaced the coil, and all of the plugs(Nice new Denso Iridiums, and a Denso Coil ;) ) It made the misfire counts go away, and made only a slight difference in the odd way its running. Even went as far as swapping injectors ( i have access to a lot of stuff being a mechanic lol) to no avail. Hell, I even changed the throttle body and all accompanying parts, and drove it for a few days STILL having the same issue.

UPDATE: P0430- Cat Efficiency- Bank 2. Just reappeared. I think this time it might actually be the Cat. Have replaced the o2 sensors twice, and this time. The truck has 230,000 miles on it.....it was only a matter of time lol.
 

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Discussion Starter · #18 ·
ANOTHER UPDATE!: Customer has his 01 Tundra at the dealer, with EXACTLY the same issue... acting identical, to include, when it does it, how it feels, and clears up on its own exactly the same....... The delaer has NO IDEA what it is so far. THey said throttle body...replaced it....didnt help (same as me).... Hopefully they figure it out... so maybe I can fix mine lol. They have had it for almost 2 weeks and are as baffled as I am.
 

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Discussion Starter · #19 ·
Update #2: Dealership here in Ocala still has no clue. Returned the vehicle to the owner and said, drive it until it gets worse! LOL Oh lord..... Just another strange mystery... Ive been doing this for 25yrs, and have NEVER been this baffled. I always have figured it out... whether 1-2 days later, or whatever.... Jeez.
 
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