2000 Tundra Idle Problems

Hi all I have a 2000 Tundra that has sat for awhile. Went to fire it up yesterday and it started no problem but has a hard time staying at idle and almost stalls. I let it idle for 20 minutes or so before driving.

Started out coughing and struggling a little but after a few minutes ran strong and didn't seem to have any issues once up to speed.

Any thoughts what could be causing the rough idle? Truck has 265k on it and has had an 02 sensor warning for 10 years but never cause a problem.

 

Which engine do you have?

 

4.7 V8

 

Which sensor, upstream or downstream? Leaving an upstream O2 sensor in a failed state can absolutely cause a myriad of problems and really fuck up an engine with time because the ECU can't decipher whether it's running rich or lean, adjust fuel trims, etc. Not to mention clog your cats on that bank.

What regular maintenance do you do? Like, have you cleaned the MAF lately, do you change your air filter regularly, are there any mods?

 

Not sure if it is upstream or downstream. I have had multiple mechanics tell me not to worry about the 02 sensor that it wouldn't cause any issues for me thats why it was never replaced. MAF hasn't been cleaned recently, no major mods just a duel exhaust. Regular oil, filters and other maintenance but like I said the truck has been sitting for over a year not being used.

 

Well, your mechanics either don't understand the full purpose of an upstream O2 sensor, or it's popping codes for a downstream sensor, or you need to find better mechanics.

When was the last time you scanned for codes? What code are currently set?

Did the battery go dead/very low while sitting? Dead battery or unhooking the batt for more than 5-10 mins will cause the ECU to lose its tune, and it'll often run rough at the next startup, until it re-learns. Relearning may also be impacted if - surprise again - you've got a bad upstream O2 sensor.

Do you have mice where you live? If yes, they like to get up under the manifold on the V8 engines to nest, and will sometimes chew thru knock sensors and starter wiring. You'll find a related code set if you read the codes.

You're not giving us a lot to run on here, though.

 

Im guessing it is a down stream sensor. Like i said its been throwing the code for the sensor for almost 10 years and everyone that has looked at it says not to worry, probably 5-8 different mechanics over the years.

Battery did die yes, just replaced with new battery yesterday. No issues at all starting up, just at idle. Don't have a scan tool so i dont know what codes are being thrown.

I don't have much to give thats why im asking for help here...

 

Any major chain local auto parts store will scan codes for free. But here's one more reason why you can't let something like an O2 sensor go unrepaired, regardless how stupid some people might think an O2 sensor is, or how inconsequential: For all you know, there's another code being thrown right now that would give you your answer without posting on the internet, but you'd never know it, because you've got a check engine light on for what is probably a $40-50 part if you buy the OEM brand (Denso brand, which you should, with O2 sensors, at least on these trucks).

You have plenty to give. Things like ...

• If the check engine light is on, is it solid or flashing (flashing = really f'n bad)?
• How long have you driven it since the new battery?
• If it's been more than a few trips and 20-30 miles, is it still running rough at 1st startup ?
• If it hasn't been running rough since, I wouldn't sweat it, the problem is likely just that the engine was needing to re-learn, and you need to now get off your ass and get some maintenance done.
• Did you check the condition of the gas before you started up to make sure it's not bad? Sitting that long can land you with bad gas, leave an engine knocking, and cause a bunch of other probs.
• Knowing rodents are a problem with these trucks, have you checked for signs of rodents? Something as stupid as them getting in the airbox and chewing the air filter, then having a chunk fly off and into your MAF would cause the exact problem you describe. I mentioned another possible problem. They also like chewing on parts of the gas tank, which will cause an EVAP issue that could cause problems.

 

Thanks Shifty this is what im looking for. Places to start looking. I get the sensor thing but if im being told dont replace the 02 sensor its not an issue why would i replace it?

There currently is no check engine light on, when it was on it was solid and i was told it was the 02 sensor.

I've driven it probably 10 miles with the new battery in it, still has a hard time idling.

Gas was one of my thoughts yes.

Just trying to save some money and do some of the work myself and just need places to start. Not super mechanically inclined so I don't know things like the engine needing to relearn after a dead battery. To me it seems easier to ask for help on the internet then spending money on stuff i dont know how to use or know what codes mean.

 

Is it the same gas since it was parked? How full/empty was the tank left?
If it’s low I would throw a whole can of Seafoam in the tank, top it up with some quality gas and take it for a spirited drive, at least that won’t hurt anything
Maybe worth cleaning the throttle body, could be gummed up a bit.

 

Look, I hear you. But, basically, for the exact reason I just mentioned. Car manufacturers put that light there for a reason: So you see the light and say, "Oh shit, something isn't working, I better get that checked out". If it's on all the time, how the heck are you supposed to know when the next thing goes wrong? What if that next thing is something that costs big $$$$? Is ignoring a $30-50, or even a $100 part in this case, really worth thousands in repairs? This is why I say, "You need new mechanics, bro".

This can be explained by the dead battery also. Lack of voltage would lead the ECU (computer, in case that's not clear) to 'forget', triggering a re-learn sequence, which nicely explains the absence of CEL and the rough idle.

I'd give it time to finish a full re-learn/readiness cycle, and I'd probably dump a can of Seafoam and a can of HEET (red bottle) in the tank to knock everything loose on the fuel side. How much gas is in the tank currently?

Hell yeah, you came to the right place then. As long as you don't get offended when people talk direct and without using soft words sometimes, and potentially rib you here or there, at least

 

This is the one thing I wouldn't do, only because others on here have found the exact same symptoms OP is describing after cleaning the TB - ECU was trying to run with same learned parameters it used before cleaning, and after cleaning, the engine wasn't the same, so those paramaters didn't allow a smooth idle

 

I defer to you on that, I hadn’t heard that experience before but it sounds logical. What about cleaning, disconnecting the battery again and forcing it to relearn?

 

Haha for sure, probably would have helped to mention im not super mechanically inclined but im definitely not easily offended. Thanks again for some starting spots.

 

Yea same gas probably about half a tank, i was going to get some seafoam and heet and top it off to see what that does.

 

Also, your CE light could be burned out from being on so long. Mine is.

 

Whatever you do, don't let anyone ever tell you the fuel filter is your problem. It's the one thing that is never the problem, but too many people replace anyway, and see zero benefit, but inevitably end up with a face full of gas, busted knuckles, and a stream of expletives out the mouth.

I don't disagree with Ben, though. A can of CRC brand MAF cleaner to clean the MAF, and a can of CRC throttle body cleaner from the parts store can't hurt for future maintenance when you're ready. But ask for tips about cleaning the throttle body before you dig in, there's some AHAs you need to know about. You may also want to take a minute to read this thread before you get too deep in repairs.

Need to finish relearning first.

I'll openly admit, I often overlooked the 'cleaning TB' thing causing problems. Then someone posted a thread here in the last year or so which @BubbaW solved, IIRC. OP had cleaned his throttle body but didn't mention it? I'm fuzzy on it, just like everything else.

 

If the battery was dead for say 6 months or longer would it take the re-learn process longer to finish? Not sure when the battery actually died.

 

Nope. Same amount of time to get there. Driving around in varied traffic conditions is ultimately what's going to get you to completeness/'readiness' state faster.