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Discussion Starter · #1 ·
I have a 2001 v8 4.7L tundra. It's idling roughly and continues to learch/shake a small amount while driving at low speeds, but once it has warmed up after a good amount of driving the rough idling goes away. No check engine light or codes to help me.

So far I have:

Replaced all spark plugs and checked the ignition coils (coils are all about a year old)
Cleaned the MAF
Cleaned the throttle body at the butterfly valve but just in front where I didn't have to remove the whole throttle body
Checked for vacuum leaks using propane (though I'm not 100% I checked everywhere, mainly I focused where hoses are cracked at their ends)
Replaced the PCV valve

I am pretty much new to doing my own mechanical work, but really want to learn. Really appreciate this forum and all of the good information people share.

Thanks for any help!


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Just a thought... May sound totally off base but MAYBE the computer has not totally settled in from all of the work you have just done.
You have hit all the buttons that I can think of so here comes my thought. Hard Boot the computer. Disconnect pos cable from batt. Turn on your lights or hit the horn button to drain residual power from system. Wait 10 minutes and re connect pos. cable. Drive a hundred miles or so and see if it mellowed out.
Usually after rebooting you will notice a faster idle speed while everything adjusts and establishes the new settings.
May seem crazy, but it's free and easy to do. Chap
 

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Replace those vacuum hoses!

What you said.
When you have a picture of a dry rotted hose with a huge crack up the side of it, on your 21 year old engine, thats some pretty low hanging fruit to start with.
 

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while mine is a V6 we are the same vintage. I had a throttle position sensor cause weird hesitations at different RPM's, I also had a temperature sensor go bad. Yes vacuum hoses need to be checked, spark plug wires can eventually go bad causing strange things at specific RPM's too.
 

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Discussion Starter · #7 ·
Thanks everyone for the help. Today I cleaned the back of the throttle body and replaced all of the cracked vacuum hoses. I took it for a test drive and no rough idle, but its so intermittent that it is hard to say if I solved the problem.

I noticed today that the front left corner of the air filter was dirty. Made me wonder if there is a bad seal there, and if that might be the vacuum leak causing the rough idle. Has anyone experienced this?

I ordered a toyota air filter a few days ago to replace the filter i bought at a local parts store, just because I wanted to make sure that wasn't an issue.

Thanks again for any insight
 

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Discussion Starter · #9 ·
Still haven't solved this. Replaced all the obviously cracked vacuum hoses

Got a fuel filter so ill replace that soon.

This problem only happens when the engine is cold and goes away after driving a bit. I feel like that should be a huge indication of something. Maybe a hose is expanding with heat and the vacuum leak then stops? Any more ideas?

Really appreciate any advice - I have a big hunting trip coming up and I really don't want this to become a problem!
 

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Discussion Starter · #12 ·
Another update on this rough idle problem. Hopefully whatever information I get in the end will be helpful for someone.

My rough idle very gradually got worse until I finally got a check engine light (never thought I would be happy to get a light and codes but I really want this resolved....)

First it gave me p0300, then the light shut off, then a couple days later I got a p0308 code.

I replaced the #8 coil and plug just to see what would happen, and the rough idle is completely gone, runs very smooth. No sign of coolant leaking or anything weird on the coil/plug I removed.

The ignition coil I pulled and replaced is only a year old or so, but it's from 1A auto and I am wondering at this point if the problem is that I bought cheap coils. I plan on looking into using a multimeter to test the coil I removed.

My question now is whether I stick with the appointment I made with a mechanic in mid November. It seems like the coil was the problem, but I am also wondering if it's some greater problem that cause the coil to go bad.

Any thoughts on this from those of you with more experience?!
 

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A couple of things. If it is running fine don't mess with it. Also, give 1A Auto a call and tell them about the coil going belly-up so soon. They are great to work with and may even replace the coil. Worth a try.
Glad to hear it's running fine, thanks for the update... Chap
 

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Never had to replace a coil myself but read a lot of threads on here and common theme is yes, stick with OEM for things like coils.
And if it were me, I would cancel the trip to your local shop. Its not like you cant do it later if something comes up again but for now, dont bother as long as its running well.
 

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Discussion Starter · #15 ·
Another update on this mystery..... More things keep breaking and I just keep replacing them. Hopefully I am not wasting money...

To sum things up as short as possible:

  • Had a rough idle but coils and plugs were about a year old from 1A auto, so I started by doing everything else:
  • Replaced fuel pump, cleaned throttle body, ran injection cleaner, replaced cracked vacuum hoses and checked for leaks, replaced air filter, replaced PCV valve
  • Missfire continued, but CE light finally came on for missfire in cylinder 8 so I replaced the coil and plugs and rough idle stopped
  • A couple weeks later missfire started and light came on flashing, code for cylinder 6. I replaced the coil and plug and it stopped.
  • After a few weeks of the engine running well, CE light and p0155 code came on so I replaced O2 sensor bank 2, sensor 1.

I was hoping I was finally done with this sh**show, but walked by the truck yesterday and heard a whining noise from the truck. I opened the hood and narrowed it down to the relay for the fuel pump. Truck is off and the relay is making a high-pitched whining noise. I disconnected the battery, made sure terminals are good, reconnected, and it is doing it again.

Heeeeeeellllllpppp! About ready to drive this truck down a boat ramp and into a lake!
 
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