Superpilot

My 2000 Tacoma 4x4 5vz-fe runs really rough with a bouncing idle and doesn't get up to the 1000-1500 warm up RPM like it should when it's COLD, it just sits at about 800 and varies by 50 rpm and runs really rough. It hesitates under acceleration till it warms up. The engine code points to Lean Fuel Mixture in Fuel Bank 1. Cleaned the MAF already. Just bought a fuel filter (it probably won't work ), any other ideas??? Try Seafoam maybe. I've never done it, just stick it in the tank? Reset the codes after cleaning the MAF and drove it warm and the check engine light stayed off, but in the morning it came back on. Seems to run better when it's cold outside, but that may be my imagination

mrfish

I am having very similar problems with my 99 4runner (5vzfe). Idle is very rough when cold, we're taking swings of 400-500rpm, but it settles out when warm. Replacing the spark plugs fixed the problem for a few days. I also have the P0171 code, so cleaned the MAF, but no luck. If I find the solution I'll post back on here. How is your throttle response when it's warm?

Superpilot

Throttle is a little sluggish, feels like when I step on it there isn't a whole lot of response, it just gets louder and slowly speeds up until it shifts gears (automatic) It started missing a little going up hill today. As the truck slowed down up the hill I didn't add power and it started missing untill I gave it a little more gas.

Superpilot

Some of the stuff on here points to Throttle Position Sensor, or Spark Plug Wires.

brian2sun

Could be the front O2 sensor... that has an effect on fuel mixture also. Any of you missing any coolant? I ask because if it's making it's way into the combustion chamber via a leaking head gasket, it could cause the same symptoms (coolant leaks in while it's sitting and takes a little while to burn off once it's started - that could be why it runs normal after it warms up a little), but you would notice your overflow going down pretty regularly.

Superpilot

No, I had read about the coolant thing, but it's pretty steady haven't had to fill it in over 8 months. It's the fuel filter, then Seafoam then The o2 sensor for me. Would that first O2 sensor cause something like this? I found the second one, but where is the first one? I assume it's hard to get to.

Superpilot

Wouldn't the O2 sensor cause a lean condition in both banks, not just one?

brian2sun

The 1st (front) O2 sensor is located before the cat and the 2nd is after the cat. They're both easily accessible. Getting it disconnected can be a little tricky so read this before you do it:
http://www.4x4wire.com/toyota/4Runner/tech/O2_Sensor/

It stands to reason. Test their voltage to see if it's in spec before you replace them. I would clean out the throttle body and IAC too since it's easy and the OEM gaskets are cheap - like $10 for both the IAC and the TB gaskets together. Test the TPS sensor too.

eddieleephd

https://www.yotatech.com/wiki/index.php/Seafoam
above seafoam wiki read.
as well as the tps it also could be as easy as air in the coolant line to the throttle body. the temp sensor there is effected by this and could cause this issue. I remember pulling the line off that runs out the back to a tube running down the back of the engine for a second to make sure that there was no air in this part of the line then quickly reconnecting while running.
or maybe the IAC itself. just a thought.

Superpilot

It does run better on mornings when it's colder. Not nearly as rough. At least 60 degrees or colder, and the colder the better it runs.

eddieleephd

Start with my last post for remedy!

Superpilot

So it's pretty easy to put the hose back on while it's spewing coolant? I'm going to try it tomorrow when I finally get back home.

okie81

As eddie preluded to, clean the throttle body & IAC while you're in there....it may not fix the idle issue, but it's good maintainence.

eddieleephd

yes there is hardly any pressure. if you pull the TB off and clean it there will definitely be air in there. However you will see the line I am speaking of easier and know it is clean. at the back of the engine where the hose from the back of the throttle body connects to a tube there should be a clamp you can just squeeze with pliers and back off so you can pull the hose. move the clamp break the freeze then start the truck "do not disconnect until it is running" walk around pull the hose off briefly till water/coolant comes spewing out reconnect.
This will make a mess if you do not do it quick enough. This is quick and easy.
for the TB gasket have some heavy oil to reseal then re-torque.