Bucking when accelerating, surge at idle.

Hi all,
Just picked up a new to me 2002 xtracab Tacoma 2.7 4x4.
When idling the rpm will fluctuate up and down( all under 1000). Get down to low 600 and up to 800's.
When accelerating from a stop the whole truck JERKS/LURCHES consistently as the throttle is applied.
This will continue through multiple gears as long as rpm is over 2000. Can be cruising at 55mph and apply throttle and it will start to jerk.
Other noticable effects are the 4wd shifter vibrating/ shaking and the gear selector shaking.

No codes, (EDIT: P0171 PENDING CODE) I have changed the spark plugs, air filter, taken apart the throttle body and cleaned it along with IAC. Also cleaned MAF. (EDIT: afr is fluctuating between 12:1 and 18:1 when surge is present.)
I use the torque pro app to monitor data but not sure what else to look at. I have values for timing, air-fuel ratio, MAF.

I will be replacing the IAC, throttle position sensor and fuel filter once they come in the mail.
I have been reading forums and watching videos for days but haven't found anyone experiencing the same issue who has found a solution.

 

Also, when accelerating from a stop or while driving and the truck begins to jerk the rpms are not fluctuating up and down, they are remaining for the most part consistent.
I am not sure if this is an electrical problem ie. a sensor, or a mechanical problem or possibly a drive line problem.

 

Did you get the truck with the issues or are they more recent than that? Any info from the previous owner as to what work they may have done to it? Sounds like something you would definitely notice on a test drive and want to inquire about.

Sounds like you're on the right path to track it down. Only other things I can think of atm:
1) Check all of the vacuum lines, make sure they look good/no cracks
2) Check for leaks on the air intake, especially after the MAF, replace any gaskets if you can get them for a good price

I like the idea of swapping the IAC, they can easily become clogged and cause issues. Not sure the TPS will fix your issues since it would throw a code if it was this bad...I think, but if you already ordered it might as well try.

Best of luck on your hunt. Hopefully someone else will have some fresh ideas

 

Bought the truck with the issue although it wasn't as pronounced during the test drive. No information from the seller unfortunately. They bought it from auction but the vehicle history shows it was a 1 owner before that with plenty of service records.

I had heard that a bad u joint can cause bucking but I've never experienced that in the past so I have no reference if it's a similar bucking/ jerking.

 

If I were in your shoes, I would start with the basics and the knowns... If you can't even get it to idle steadily then that would be a red flag in my mind and where I would start. Bad driveline components can certainly cause bucking and such but they won't have any impact on a stationary, idling engine. Of course the engine will idle higher until it warms up but throughout that process and after, it should be a pretty steady rpm, not constantly hunting as it sounds like you might be experiencing.

Going back to the basics, I think there are few more things you could check for air/fuel/spark:
1) AIR- sounds like you have checked the air intake up to the MAF but it may be worth checking as far as you can reasonably do right up to the combustion chamber (what I suggested previously). You could also group checking the vacuum lines into this
2) FUEL- I wouldn't expect this to be a fuel issue, if it were I think it would be more pronounced with the engine cutting out at higher rpms but it sounds like you can get it up there on occasion, just with some bucking/surging. Easy thing could be to check the gas in the tank, if it was an auction truck could be old/dirty. Maybe siphon out what you can and replenish with fresh
3) SPARK- You said you changed the plugs, how did they look? Happen to ohm check the plug wires or coil packs while you were there (assuming an 02 4-cyl has those, Im not very familiar)? Coil packs are very reliable iirc but plug wires can wear out and would certainly be worth checking.

^that's where I would start if I were in your shoes. Wouldn't hurt to go over the driveline and to check all of the fluids if you wanted to (good to do with any new vehicle) but getting a steady idle and stationary revving would be my priority.

 

Try a new valve cover gasket but more importantly the spark plug tube gaskets. Good luck!

 

I've seen simular issues like that before but on 2 different cars, and both times it was the cat that was clogged.
Both cars where manual, when you drove it, it pretty much felt like you didn't know how to drive manual. As soon as you let off the clutch and give it gas it would buck and jerk, push clutch in, it would stop.
If that sounds like what yours is doing, I would check the cat.

 

So I've been doing what diagnostics I can and I've found a few things.
When first starting the truck it idles normally for about a minute with the air to fuel right at 14.7:1 then it starts to faintly surge and the air to fuel ratio starts fluctuating from around 12:1 up to 18:1.

I also was able to pull a code for the first time since this has started, it is a pending code p0171 bank 1 too lean from what it said.
I inspected all the vacuum lines I could see and couldn't find any cracks unfortunately. Really not sure where to look now.

 

This is at idle

 

Thats great you got a code! Im not familiar enough to know how far off of normal those numbers are but if the code is saying its lean then that's pretty definitive and should help you with your research.

Im still leaning towards an air intake leak somewhere, but that may just be because I have experienced it before. You could do a propane test pretty easily to rule that out if you're willing. Beyond that I think you will have to start looking at a repair manual to check/replace sensors as you narrow it down.

Best of luck on it and let us know when you get it figured out.

 

I'm just starting to look at the catalytic converter now too, it has a very noticeable rattle with the engine on. It looks almost brand new though so I hadn't considered it.

 

I had no idea that a bad valve cover gasket or spark plug gasket could cause an EVAP leak or even a rough/surging idle.
I see no visible signs of the valve cover gasket leaking so maybe it's ok
I will mention that when changing the spark plugs there was a bit of oil in the tube and the coils looked stained/burnt oil had been on them. The plugs were also pretty loose (hand tight) so that could explain that.

 

changing the spark plugs there was a bit of oil in the tube and the coils looked stained/burnt oil had been on them

That’s what im talkin’ bout

 

I can’t remember if the 2.4l used the double probe style spark plugs. I don’t think it would cause this much trouble but if you put standard plugs in it look at that maybe.

 

I did do some checking online before replacing the spark plugs and from what I saw the 2.7 did not take dual electrode plugs. I have denso platinum plugs in it right now gapped to .44

 

Am I right in thinking I should be focusing on the wacky air to fuel ratio first? Going from 12:1 to 18:1 consistently should point to a vacuum leak right? Or would something else cause that

 

Truck is going in for emissions today, hopefully it can still pass with these symptoms. Will update later

 

Failed emissions

 

Shit

 

UPDATE:
so today the truck threw a code, P1135. Which I believe is the pre-cat O2 sensor.
Does anyone have any input here? Could the problem be a bad O2 sensor or do you think it's more likely that the problem CAUSED the O2 sensor to go bad.