Multiple engine codes; P0440, P0100, P0110, P0120. 1999 Tacoma 2wd 2.4l 5 lug

1999 Tacoma 2wd 2.4l 5 Lug, 252k miles.

I've had the truck for only about 500 miles. Ever since I bought it, it's ran a little rough with the occasional once a day dip in RPM for a split second, but I'm not sure if that's just indicative of an older vehicle or if it's an actual issue.

Once it's warmed up it idles high at around 910-950rpm. I think normal idle for these engines is 650-700. I'm guessing I just need the idler screws adjusted, and maybe the IAC cleaned.

Aside from that, I scanned for codes and found these.

I believe P0440 is the one that triggered the engine light and the other 3 were just there in the background, but not certain.

So far I have only re-seated the gas cap and cleared codes, they haven't came back in 30 miles so far.

I think the IAT/MAF sensors are both part of the same module right behind the air filter but may be mistaken.

Any ideas on where to start?

 

The MAF and IAT are one in the same.
Both are part of the MAF sensor.

I'll pull diagrams and checks. See where you can go from there.

The TPS could be on the same circuit. I need to look.

 

To start with, on your scan tool.
What does the IAT temperature read?
Key on, Engine Off.

 

I read from a similar post with same codes that all 3 (IAT,MAF,TPS) all share a common ground wire in the ECU. Not sure how accurate that is but it may help.

I'll get that reading tomorrow as soon as I can. I ordered a regular wired OBD2 scanner, this wireless one I have is awful and takes forever to connect (if I'm lucky).

Does it matter if engine is cold or warm, I assume not but just in case.

Also thank you very much for your help!

 

Not really, we’re looking for numbers close to an outside air temperature.
What we don’t want to see numbers way outside of range. The reason I asked was because typically, this is easily checked on a scan tool.

I’ll see what the 3 share in common, but we don’t need to get too far off course.

 

They do share the E2 ground, but that doesn’t mean it’s the ground.
We can test it I guess.

Key on Engine Off.
Unplug the MAF
See if the ground is good on the Brown/Black wire.
Might as well check for power on the White/Red wire while you are there.

 

So I just pulled the temp and the IAT is reading 71F or 75.2F depending on which OBD2 app I use. Seems about right to me since it's 61F outside and there is residual heat left in the engine bay from driving earlier.

MAF also looks fine.

As for the TPS it's reading 10.59% with engine off and ignition on. I think it's supposed to read closer to 14.5%, and 10% is the absolute lowest it should read if you manually push the throttle all the way closed. I didn't get a chance to check that because it's pouring rain right now. But I don't think that little of a difference will affect anything.

Not really sure where to go from here, not seeing anything out of the ordinary. I do have a multimeter but I have no idea how to begin diagnosing with it.

I was hoping these codes could be a cause for the rather violent shake at idle. Idk if that's just normal for this engine/truck but I can see the hood jump up and down 1-3mm during idle and the shifter shakes left and right about 1/2".

See below images

 

Run a compression test on the motor before you spend and money on parts.

 

Why do you say that?

 

Not what I was hoping to see.
Those numbers look good / normal.

It's almost like you are having an intermittent issue.
You say it stumbles once in awhile before.

I'd maybe fire up the engine.
Let it run a bit until the engine is warm.
At idle it should show about 2.5-3.5 gm/sec.
Kind of want to see if the signal is dropping out.

you can also monitor the TPS %
see if they are in spec.

 

IMO
Think P0440 separate issue
Unless charcoal canister filled with fuel
The other 3 codes focus on:

 

The one constant in all the above codes is ‘electrical connection’

like Austin1346 stated could be ground
I would trace/inspect all harnesses from TPS/IAT/MAF and report back

BTW
Compression Test is a great/cost effective way of ‘getting to the bottom of things’
Lots of people just don’t want to find out the worst, but feel better about tossing parts at the problem
(Believe me….been there done that)
And the $40 compression gauge can be used again and again

 

So today I will:
1. Verify TPS range is in spec.
2. Verify MAF reading is correct at idle and warmed up. My scan tool can graph it over time so it will show any drops (if they occur while I'm watching it).
3. Check and trace wiring from MAF/IAT and TPS.

I've checked online for high idle issues in same gen Toyotas and almost always it ended up being a dirty idle air control (IAC) valve.
If I don't find anything from doing the above I think I will try and clean the throttle body and IAC this weekend. Will have to buy a new TB gasket though first.

I'll scan it again today after driving about 30 miles to see if any codes came back. So far no check engine light.

 

So I just drove about 80 miles round trip and all the codes are still gone. I think someone may have just disconnected them at some point while the ignition was on and they just needed to be cleared.

However, I noticed my idle is fluctuating between 750-850rpm after warmed up. Image below. Notice the throttle position isn't changing so I'm led to believe it's the IAC, or less likely the throttle body butterfly not sealing, or combo of both.

In another thread someone was saying they had a worn out throttle body and the butterfly valve was stuck open a bit, and the IAC tries to compensate and it just goes back and forth in this loop which creates the idle fluctuation.

I think my next course of action is to clean throttle body and replace IAC. I'd just try cleaning the IAC but it's probably on it's way out at 252k miles anyways. Maybe the TB has some carbon buildup that's not letting it close fully.
EDIT. Nevermind I'll try cleaning the IAC first before replacing, it's $250 brand new haha


Also wanted to confirm my TPS is within spec (10.2% at idle, 76% at wide open throttle)
MAF is also reading correctly
All wires and connectors look normal.
Also wanted to clarify the A/C was NOT on during these readings

 

as far as the TB butterfly valve gap.....i dont think it is an issue
when i was searching about cleaning IAC/TB few months ago
proof (IMO) is this thread

https://www.tacomaworld.com/threads/stuck-high-idle.509642/page-3#post-22612251