2004 2.4 5 speed running lean

Hi, I am new to this forum. My Taco has 85,000 miles on it. My problem began after replacing my up stream O2 sensor because of a CIL (got diagnosis from AutoZone). I had recently replaced the down stream with a non OEM without a problem, so used a non OEM On the Upstream. After replacing the Upstream O2, my truck ran good until it was warmed up. Then it would jerk at in 1st, 2nd and 3rd with normal acceleration which I think means that it was running lean after the engine was up to temperature. I assumed that O2 sensor was defective, returned it and replaced it with a different non OEM sensor. Same problem both times, no CIL, so, I think something else must be wrong. I have since replaced the MAF sensor, Throttle position sensor, and fuel pressure regulator...all with OEM parts. The lean problem persisted with no CIL. I finally replaced the second upstream O2 sensor with what I thought was a Denso OEM sensor (

234-9001 Air Fuel Ratio Sensor

234-9001). The lean running problem went away. My truck ran good, but the CIL came on. I found out that Denso etches the part number and I took out the sensor and found out that I had been sent the wrong Denso sensor (it was actually for several Toyota/Lexus V6 engines). I replaced this with the correct Denso O2 sensor. CIL went out, but lean running engine returned. I have since replaced the fuel injectors (with Denso's). Lean running engine is still the same. I am at my wits end. Sorry to be so wordy, I would appreciate some help figuring this out because I love my truck.
Redeye

 

What do you mean by jerk in 1st? Does it stumble? Do you notice a dip in RPM's? A lean condition would almost certainly throw a code

 

Unfortunatly as you have discovered the code(s) from the PCM (Powertrain Control Module) are symptoms and do not necessarly mean "replace this part". Without an OBDII scanner that can show live data you will be throwing parts and pulling hair. A small exhaust leak at or in front of the upstream sensor will trip a CEL. That is inexpensive an often over looked.

If you do manage to have access to an OBDII scanner you are going to want to focus attention on the STFT and LTFT (short and long term fuel trim). Ideally they should be + or - 5%. To trip the CEL for a lean conditions means that the PCM has modified the amount of fuel injected up to its maximum (+25% or more ) and the front air fuel sensor is still not showing what the PCM it is expecting to see. Is this truley a lean condition or is there a problem with the A/F sensor? There are ways to test the A/F sensor with propane enrichement and watching how the A/F sensor reacts or doesnt react.

Your problem might be the sensors at all... it ALL starts with the fuel pump. If the pump cant build or maintain the proper pressure or volume how do you think the injectors will react with low volume/pressure? They inject less fuel and you get a lean condition.

My advice is that if you do not have access to any or all of the tools to do the testing find a shop that does. You will be $ ahead and with less frustrastion. How do you find a shop if you dont know of one? Locate your local NAPA, O' Reilly etc and ask one of the older parts guys what shop returns the fewest parts. The shop that returns the fewest parts means that their techs can diagnose whereas the other shops are shotgunning parts until it gets "fixed" or the customer goes away in frustration.

Good luck and tell us what you have done/discovered.

 

Speakerboy, By jerk, I mean that it feels like I an giving it the gas and letting off while accelerating in 1st, 2nd and 3rd gear after the engine is up to temperature. The symptoms are much less in 4th and 5th. Also if I floorboard it, the truck accelerates without jerking.
Glamisman, Does PCM and ECU mean the same thing? I only had a CEL when the original A/F sensor was bad and when I installed the wrong A/F sensor. When the CEL is tripped, I get a P0171 and a P2237 codes. I do not get a CEL or code with the correct Denso A/F sensor. I believe that the PCM is setting the wrong STFT/LTFT after the engine is up to temperature.
I do not believe that there is a fuel pressure problem since the truck accelerates w/o jerking when floorboarding or accelerating in 4th and 5th.
Can the PCM be reprogrammed to correct the STFT/LTFT if that is the problem. If so, I will try to find a shop with that capability. I live about 35 miles from Tyler and will look for Google ratings on shops. I might have to use the Toyota dealer.

 

Yes ECM and PCM mean the same thing.

the observation about her only running poor after she is up to operating temperature is important. The PCM has 3 states of operation, closed loop... all of the various sensors are used to manage the engine/trans, open loop... she is cold and a predetermined set of parameters are used to get her up to temp as fast as possible, limp home... the CEL is on and a fixed set of parameters are used to get you down the road and hopefully not damage the engine/trans/catalytic convertors.

No the PCM can not be reprogrammed for the fuel trims.

I have never see a P2237. I had to look that one up. I think that that code was set because the incorrect A/F sensor sent a voltage reading back to the PCM that was out of acceptable range.

 

Sounds like you might have a vacuum leak letting in air somewhere past the MAF sensor. Check all vacuum lines. Check the plastic intake tube for a loose fitting or crack. Check that intake manifold is tightly secured to head.

Look up ways to check for vacuum leaks. Usually involves spraying something like starter fluid around vacuum lines and intake and seeing if idle speed changes.

 

Glamisman, I understand completely "limp home" I had a 2001 Jetta TDI that blew the inlet air hose off the turbocharger. As you can imagine it would barely run. I disconnected the MAF. It went in to the "limp mode" and ran great. This could possibly what was happening when I was using the incorrect A/F sensor.
DrZ. I agree, it is probably a air leak downstream of the MAF. I took the PCV out, cleaned it and hear something rattling around in it. I can blow a lot of shop air through it from the valve cover side. There does not seem to be any restriction. This is probably a cheap item and I will try replacing it. Also, there is a strange hose that goes from the valve cover to to just in upstream of the throttle Valve butterfly. Does what it's function is? See attached picture. Both the PVC hose and this hose are in good shape and do not appear to leak.
I am curious about the odd plastic housing between the MAF and the Throttle body. I do not think it is leaking air, it just seems unnecessary.
I am going to get some starter fluid and check for leaks.
Oh, another thing. I think that there should be a EGR valve, but I do not see it.
Thanks,
Redeye

 

I would start by putting an OEM (Denso brand) sensor in...Toyotas are built using Denso sensors and designed to run on their exact specs. Aftermarket sensors are known to be a gamble and cause issues

 

eon_blue, I started a month ago with a

Denso 234-9001 Air Fuel Ratio Sensor

Denso 234-9001 perhaps you did not read far enough up.

 

The PCV valve is a one way valve. You should hear the check valve rattle when you shake it. That is normal.

 

the plastic box attached to the intake tube is a pulse dampener. I was told it is to reduce noise of the incoming air. All hoses from motor to intake are emissions related.

 

I installed a new PCV valve and it solved the problem. Yes, it is supposed to check the flow from the intake in case of a backfire, but it is also supposed to restrict the flow from the crankcase during high manifold vaccum. As I stated, I applied shop air (100psi) to the pcv crankcase side it blew out the other end with no restriction. With the new valve, I tried sucking on the intake manifold end and could sense the restriction. From what I have read, the pcv consists of pluc with a weak spring in a tapered chamber designed to stop the flow in one direction and restrict the flow in the other. Truck now runs great, no jerking.