Misfiring, running lean, idling high?

I'm new here, so let me know if I'm missing anything, but I tried searching the issues I'm having and didn't see anything--so here goes:

I bought a 2000 Xtra Cab, V6 Manual TRD Tacoma three weeks ago with 172k on it. It's in stunning shape with full maintenance records and has been running great until now.

Four days ago I noticed it was idling really rough. It was actually rocking the entire truck from side to side. This got progressively worse and started acting the same at low (under 2500) RPM. Then, a couple minutes later the CEL came on!

I pulled over and popped the hood. The engine was rocking pretty violently. I don't know a ton about cars (yet!) so I called my mechanic friend. He said it sounded like a misfire and was hopefully a spark plug/ignition coil issue. I drove it home (7 miles) very gently. By the time I got home the CEL was off, but the engine was still rocking.

That was Friday. I went out of town over the weekend and when I got back on Monday morning I ran the codes. I have the Actron OBDll pocket code reader and either the code didn't get stored, that reader is cheap and can't retrieve stored codes, or I don't know how to retrieve it (yes, I read the manual and couldn't find anything about retrieving stored codes). However, it did have a pending code of P0171 which is the "running lean code".

When I started it up, it wasn't rocking anymore (no misfiring). I drove it about 5 miles to warm it up and it ran smooth the whole time. However, it was idling at about 1500RPM (no heat or AC on), and before this it idled around 600RPM.

The next day I drove into work. It was still idling at about 1500RPM for the first 10 miles, UNTIL I went down a big hill and stopped at a light. During that hill, the gas light came on (I was low on gas, so that's fine), and when I pulled up to the light it dropped back down to 600RPM. Now everything is completely normal....

I don't know if all this is connected, or I have terrible luck and each thing was coincidental. I'm concerned about the reliability of driving it on longer trips now though. My next step is to unhook the battery and let everything reset. My mechanic friend said maybe the computer got confused and threw everything out of whack.

Any ideas?

 

I drove it to work yesterday because it was running fine. Then on the way home, the CEL came one again. This time I pulled the code, cylinder 1 was misfiring. By the time I got home, it threw two new codes. Cylinder 6, and running lean. So.... two cylinders, not on the same coil misfiring?

I just replaced all the spark plugs and there was nothing noticeably wrong with the old ones. I checked the coil resistance. They are

$126 Toyota 90919-02212 Toyota Genuine Parts - Coil, Ignition (90919-02212)

Toyota 90919-02212 coils. The secondary resistance is about 10 ohms, but on all three coils, the primary is zero. Like I said, I'm new to this world, but I think I'm doing it correctly.

I don't see how it is possible for all three to be shorted though...

 

Update:

Well, maybe I have no idea what I'm talking about. After posting that, I put everything back together and test drove it. No codes and it ran totally smooth. I drove about 20 miles and it's still running beautifully. Hopefully that continues.

 

Loose wire misfire. Remember what you touched or moved under there,,it might jump back again. A ground wire shaking loose could cause that as well.

 

It was running great all yesterday with no codes. Then last night I drove about 45 miles in a blizzard (so 30mph in four wheel drive for about an hour and a half). I plugged in my code reader when I got home and it had two pending codes. P0300 which is the random/multiple misfires from before, and P0450. I'm hoping the 450 will help me narrow down the hunt for what is going on... I'm driving about 120 miles tonight and trying to decide if I should take the truck or not.

 

I was just diagnosing my truck for a consistent cylinder 5 misfire. Ended up being a bad injector but since you're having multiple random misfires and lean codes, I would look more towards a fuel filter or vacuum leaks around the intake possibly causing a lean mixture. Also clean your MAF if you haven't done so already.

 

don't overlook a bad fuel pump, they can also have issues with bad connections at the plugs at the tank as well as inside the tank.

since you were low on gas my bet is the fuel filter is blocked with junk or the pump sucked up some trash and isn't working right causing bad gas supply and low pressure. (or both)

add to that the way this came right out of the blue like that

put a fuel pressure gage on it and se what your readings are before jumping to any conclusions.

 

Solved!

You guys were right. It was a wiring issue. I cleaned the MAF sensor and disconnected the battery to reset the codes. I went to reconnect it and noticed the ground from the battery wasn't fully connected to the body. Upon closer inspection I found it was totally disconnected. I was in a hurry, so I just opened up the connector with pliers and shoved the wire back in. I drove 150 miles that day and had absolutely no problems. I was elated.

Then today I was driving and it started misfiring again. I was not happy... I decided to check that battery ground again, and sure enough, it popped out again. I then noticed the strap holding the battery wasn't tightened down so the battery was shifting around, pulling on that ground strap. I got a new wire and new connector, tightened down the battery so it won't move and everything is running great again!

 

Good news. Was due for a easy fix then. Your next one is gonna suck,,be warned.

 

Looks like I rejoiced too soon.

Today it misfired three separate times, one of which turned on the check engine light.

I drove for about 10 miles, parked for about half an hour, started it up and it misfired for about a minute of driving. Then I drove about 60 miles, parked it for an hour, started it up and it misfired for the 5 minute drive. Parked for another 30 minutes, drove it and it stopped misfiring after about 10 seconds. It was very intermittent. It would misfire steadily, then stop for a few seconds, then misfire again for a bit again. I checked the codes and it was only cylinder 1 this time (cylinder 6 did before, as well as "random multiple misfires"). It also seemed to be idling pretty high.

Any ideas? I'm not sure what to tackle next. Maybe check the vacuum?

 

The mystery continues...

Let me restate things briefly so people don't have to read the whole post. If you just want to hear the most recent, skip down near the end.

-I bought a "new" 2000 tacoma V6 manual with 172k on it, beautiful condition, no issues.
-Two weeks later, it started misfiring in cylinder 1, enough to make the engine rock substantially. It also threw a code saying it was running lean.
-I changed the spark plugs, tested the coils and wires, unhooked the battery for a while--all better.
-4 days later, misfiring again. This time it was cylinders 1 and 6. It also had a code p0450--the evaporative emission control system pressure sensor. After combing through the engine compartment, I noticed the battery was loose and had slid far enough that it disconnected the grounding loop to the body. I hooked it back up, disconnected the battery again, and the next morning it ran beautifully.
-1 week later, misfiring again. This time I notice a pattern: If I drive it till it's warm, then let it sit for anywhere between 5 minutes (longer than just off and on) and two hours, it misfires when I start it back up. It either does it for about 3-5 minutes, or continues till I stop driving all together. If I let it sit for longer idling, it seems to always stop within the 3-5 minutews. Outdoor temperature doesn't matter.

UPDATE:
-Tonight I stopped by the auto parts store and used one of their live data readers. There were several weird things. First, it stayed in open loop the entire time. I even tried revving it to 2000rpm for about 5 minutes--still open loop. Next weird thing, the voltage readings on both O2 sensors was between .01-.02V. During all that revving, it misfired in cylinders 1, 2 and 6.
-I took it home and pulled the O2 sensor connectors. I checked the ground going back to the ECU and it was fine on both. I then ran the truck with them still off, grounded the (-) to the body and my voltmeter, and checked the voltage coming from the sensor--It also read zero. My friend told me to do this, he said the sensor creates electricity on it's own--is that true? Also, I should note, it did not throw any codes while the sensors were unplugged, which seems a bit troubling... and it ran beautifully without misfiring even though it was in that 15 minute-2 hour window.

So that's where I am... My first thought is something in the ECU was seriously screwed up when the battery ground to the truck body was disconnected. Past that.... I have no idea.