Cylinders 2, 4 and 6 burning lean?

Okay, so my 2000 Taco is still idling rough. It does not do it all the time, mostly when it has been driven a while and it still does not do it all the time then. This is what I have done so far:

• Checked the vacuum lines and all appear to be in good condition
• Replaced my air filter and cleaned the MAF sensor
• Cleaned the Idle Speed Control Valve
• Replace the upstream oxygen sensor
• Ran two tanks of Chevron Techron
• Replaced the spark plugs

When I replaced the spark plugs I numbered them according to which cylinder they came out of and noticed that numbers 2, 4, and 6 plugs which line up on the driver side all seem to be burning lean. 1, 3 and 5 seem to look as they should. I know that 1, 3 and 5 are on a separate fuel rail or fuel map than 2, 4 and 6. What would cause the even side to run leaner than the odd side? Could this cause my truck to idle rough?

I'll post pics of the spark plugs as soon as I can...

 

Here are plugs 1, 3 and 5



It may be hard to tell but the rim of the plug is black which is normal wear on a set of plugs.

Now here is 2, 4 and 6. Notice how the rim on these are not as black as 1, 3 and 5...

 

maybe you have a peice of debris in your fuel rail on that side that would cause a rough idle and the spark plugs to be off. they dont look too bad.

 

check fuel pressure.

 

I am by no means a professional mechanic. I pretty much learned what I do know from a friend who was a professional mechanic and I have my trusty Haynes repair book.
As far as checking the fuel pressure, how is that done?

Thanks for your response!

 

Oh and since 1, 3 and 5 cylinders are on one fuel rail and 2, 4 and 6 are on a separate fuel rail, what controls the pressure to each fuel rail?

Thanks again.

 

neither am i. i have learn from a couple of the best hotrodders in the south and my own trial and error.

well on you fuel rail you should have a little threaded fitting. this is where you would check the fuel pressure from.
here are the steps:
1. locate fuel pressure and firmly attach fuel pressure gauge (advance auto parts has them) with the vehicle off. then turn the key to the run position without starting it and this will give you your first fuel pressure reading.
2.next start the vehicle with the fuel pressure gauge attached and check fuel pressure again. the fuel pressure should remain close to the same.
3.turn off vehicle and depress the purge on the fuel pressure gauge to avoid a spray of gasoline when removing fuel pressure gauge.

the reason i say to check fuel pressure is because it sounds like you have less fuel getting to that side of the motor be cause of lack of fuel pressure on that side of the rail and/or clogger up fuel injectors.

this isnt for sure it but would be a good spot to start.

 

Thanks for the advice. At this point I have arleady invested close to $200 in what I have already done to alleviate the annoying sporadic rough idle...

 

It may be just the angle of the plug, but it seems as the electrode on plug #1 isn't worn the same as the others? Do a good fuel system clean first.

 

i have the same issue with my 2004 prerunner with the 2.7L 4 cylinder

 

I ran two tanks of Chevron Techron fuel system cleaner and ran the truck another month before I pulled the plugs in the picture out.
I have a new set of plugs and the truck still idles rough.

 

Fuel pressure should be uniform to both left and right rails you should only have one fuel pump that supplies both sides. if the pressure did change it would be because of a blockage somewhere on that side of the system. check it to the other side and see if the are close to the same then i would go from there.

 

It's not fuel pressure...as stated both rails are being fed from the same line which eliminates having two upstream oxygen sensors. I have already replaced the upstream oxygen sensor and I have cleanded the MAF and IACV so my fuel air ratio should be correct.
I can't figure out what it possibly could be that is indicative to the left side...The only thing I can think of at this point and as I stated earlier, I replaced my timing belt last summer and the belt could have stretched some causing the left cam to be slightly off. This would make sense since the rough idling is irregular but then again, if the left cams timing is off then eventually the timing will be off period. It seems to idle smooth when it is cold but gets rough after it has been driven a while.

Any more ideas will be greatly appreciated as I continue to try and solve this issue

I will be replacing the fuel filter this weekend since it hasn't been done since I have owned the truck.

 

i had my baby running lean and i replaced the tps and it seemed to fix it

 

I know im bringin this thread back but i got a 2000 as well and its running really lean. it has a rough idle and when i floor it it pings to the point where it soounds like a have a penny in my engine. Im interested to see what the fix is. I am still working on mine. Been trying to figure it our sence September

 

My 2000 Taco had been doing that and I just filled up the tank with higher octane fuel and that pretty much got rid of the spark knock. Of course this is a quick fix and does not solve the issue. It could possibly be a bad (upstream) Oxygen Sensor, I would start there first. I finally replaced my Oxygen sensor and the spark knock went away when I went back to the regular fuel.

 

the PO said he had one o2 sensor replaced at the stealership, but idk im cuttin out the cats and we will see where that takes us. after that its to replacing all the vac lines

 

Run the engine and spray carb cleaner around the intake ports on the drivers side.If the idle changes speed you have an intake leak.More then likely you are sucking air on that side of the engine causing your lean condition.Fuel pressure would effect all cylinders.Clogged injectors could cause a misfire from dripping injectors but having 3 on the same bank is VERY unlikely!! Check for the air leak.....I bet you'll find one.

 

done already and didnt find any. gonna get my bro to run a compression test on it. I already replaced a bad injector. i just want it to run smooth. I bet my pistons look terrible

 

The only other thing I can think of is if the EGR valve is ported to that bank and the pintle is not fully seated causing a manifold pressure leak which will cause a rough idle and lean condition.Best way to tell is unbolt the EGR valve,lift it up and slide a business card in and tighten it back up.It will block the EGR valve off.Run it if its smooth you found your problem.FYI.....a bad TPS will NOT cause a lean condition on one cylinder bank.