High hot idle, low cold idle, what am I fighting on 02 Tacoma 3.4L engine?

Lil'John

Lil'John

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No real short to this so this will be long unfortunately.

Target truck: 2002 Tacoma TRD 3.4L, manual trans, 4wd.

The engine has over 317k miles. The timing belt was done around 270k to 280k miles using OEM parts.

Issue: At start up with cold engine, the idle is super low; like 800rpm. When the engine warms up to running temp(middle of temp gauge), it idles super high; like 1500rpm. Gunning the engine does not drop the rpm.

Before this started, it ran well except for having two engine codes:
P0120 which is TPS A circuit issue(maybe)
P0420 which is related to 2nd o2 sensor

I was able to fix the o2 issue with new exhaust gaskets(10/1/24) but I may have ****ed the situation up with Seafoaming through the brake vacuum line in an attempt to resolve the TPS. :emb: After the above, both of the engine codes have disappeared and not returned. So now I'm stuck not able to pass smog due to high idle.

Since Oct, I have tried replacing the following to no new results:
new OEM PVC valve and hose (2/9)
new OEM IAC (12/24)
new OEM throttle position sensor (1/10)
new OEM intake gaskets (2/3) - trying to chase external oil leak
new NGK spark plugs(1/27) - not horrible shape but not correct plugs (single strap)

I know there is an internal oil leak as the mouth of the intake will show a bunch of oil as will the throttle body side. I've hosed the engine bay in carb cleaner trying to track vacuum leaks... not literally hosing it down but spraying around the intake manifold and the various hoses with no noticeable difference. I also tried removing the oil cap and noticed no difference.

I have used HP Tuner scanner and nothing is jumping out on me on the sensors.

I have not replaced the throttle body because it seems to be impossible to find the correct version: 3.4L calif edition with manual trans and cruise control. I don't have the TB number in front of me but I have searched. But I've cleaned my throttle body but there appears to be no internal passages.

Anyone have any thoughts on where to proceed?

Setting on fire is not off the table but I'd rather have a spare rig. Selling for nothing isn't on the plate.
 
Slander said:
Not that this helps you, well it may if you need a new throttle body, but this place is legit and lets you buy parts by VIN. Genuine OEM Toyota Parts and Accessories Online - Toyota Parts Deal
Click to expand...
Thank you for the reminder. I've used them some in the past. They also gave me a part number of 22210-62260 which is 'impossible' to find on ebay.

I ran into a similar issue on my Lexus with an AC ECU... the rig had two numbers showing for the year. One version works... the other doesn't give AC. Guess which version I ordered first :emb: As a result, I'm a bit more gun shy on matching part numbers.
 
I know you said you replaced the IACV, but if there was any crud or a speck of anything in the tb that got into the IACV, that would screw with that valve.

Other options, get a cheap smoke machine off of ebay and check for vac leaks.
 
Thanks for the thoughts so far.

Here is what I'm fighting. Here is cold start with 65F outside:
Taco_ColdStart_sml.jpg

No SAS:
Taco_ColdStart-NoSAS_sml.jpg

I did nothing but put the car in neutral and turned the key to fire it up. After 30 minutes of leaving it running, I came back to this:
Taco_Hot30Mins_sml.jpg

After stabbing this **** out of the throttle(5k+ rpm), here is what it ended up at:
Taco_HotStabThrottle_sml.jpg


I JUST replaced the IAC with a chicom special but here is what the OEM one I pulled off looked like:
Taco_Iac1_sml.jpg

Nothing is jumping out at me. The 'water' is from pulling it off. I didn't see any crud/oil in the IAC itself. The air hose on the IAC didn't fit snug but it wasn't super loose. There is no clamp on it.
 
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I replaced the PVC valve because it wasn't rattling earlier but it didn't resolve the issue.

When pulling the throttle body off, there was oil in intake area:
Taco_MysteryOil1_sml.jpg


Throttle body side:
Taco_MysteryOil2_sml.jpg

Not great but I don't see where it is coming from nor am I certain that it would have an impact on the idle issue.

In the second picture, you can see how I moved the IAC 'adjustment' to one extreme side. I also did it completely to the other side. That had zero impact on the idle issue. The new IAC has the 'adjustment' centered.

Any thoughts?
 
Did you run through the diag on the P0120 fault? Even though you have a new TPS sensor it may be a wiring issue or ECM.

Seems like a TPS fault would give you idle issues.
 
Skinny said:
Did you run through the diag on the P0120 fault? Even though you have a new TPS sensor it may be a wiring issue or ECM.

Seems like a TPS fault would give you idle issues.
Click to expand...
I did not run a full diag on the P0120... it had the code, I dropped a new TPS sensor on it and the code went away.

I will fire up the HP tuner and see what the TPS is doing at cold and hot idle. I will also take a look at the temp the ECU is reading.

Wouldn't a faulty TPS shift the idle one way or the other for both cold and hot idle? Ex: both go down 500rpm or both go up 500 rpm. This looks like the computer freaked out and flipped the idle tables or something weird like that.
 
After ****ing off for a few months, I'm spinning back around to this cluster ****.
Lbhsbz said:
What are your fuel trims at idle and 3000rpms in neutral?
Click to expand...

For this data, hot means 180 degree. I pulled the data using HP tuner. There were no service engine light and the truck was in neutral with clutch let out(system is currently dead)
cold idlecold 3khot idlehot 3k
rpm1200 rpm3000 rpm1600 rpm3000 rpm
tps13.7%18.5%14.1%17.6%
fuel trim short-9.4-1.6-3.1-2.3
fuel trim long12.50.09.43.9

The advance timing table went from 27 to 33... this is from 1200 rpm to 3000 rpm. There was a dip to 29 in the 2400 rpm range.

This is with new OEM TPS, OEM IAC, OEM IAC gasket, OEM throttle body gasket, OEM PCV, and OEM PCV hose. The engine is very long in the tooth with 340k+. This is after fixing a TPS and o2 sensor error codes... then running Seafoam through the brake booster hose. Before this, it ran fine minus two error codes.
 
you have a bigass vacuum leak

Let's say at idle the engine want to eat 50 units of air per minute. We have a fixed orifice vacuum leak that is passing 10 units of unmetered air per minute...this will create a lean condition and you will see a positive fuel trim as the ECM tries to add fuel to get back to stoich (Long fuel trims at idle are near 10%). If you raise the engine RPM to 3000, the engine wants to eat 300 units of air per minute, but we still have that 10 unit of unmetered air per minute leak....a much smaller percentage when we look at the total demand at higher RPM vs lower RPM....which is why we see fuel trims under 4%, which is pretty normal. These are all just made up figures to illustrate my point

Check the intake boot for cracks in the bellows, go over all the vacuum lines....make sure the connections to the intake manifold plenum are good, and then grab 'em with needle nose pliers (if the hoses are still pliable enough not to break) and see if the idle changes....could be a brake booster leaking, could be a vacuum solenoid leaking, could be a bad hose or connection.
 
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Lil'John said:
Would running Seafoam cause this issue or expose weak vacuum lines?
Click to expand...
doubt it. Just find the leak

Don't use brake cleaner/carb cleaner.....a lot of that **** doesn't burn anymore. Use a propane plumbing torch (unlit), or rig up a smoke machine somehow (find a buddy who smokes, have him exhale into a vacuum line lol....is how we did it before smoke machines).
 
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Agree sounds like a vacuum leak most likely. Seafoam probably kicked a bunch of **** loose that caused it to pop up.

I didn’t see you mention MAF - with that oil coming out your TB, the MAF is probably all gunked up and could use a good cleaning. Might help the problem, can’t hurt.
 
OldPainless said:
Agree sounds like a vacuum leak most likely. Seafoam probably kicked a bunch of **** loose that caused it to pop up.

I didn’t see you mention MAF - with that oil coming out your TB, the MAF is probably all gunked up and could use a good cleaning. Might help the problem, can’t hurt.
Click to expand...
I haven't checked how parts lay out on the truck but I thought MAF was almost sitting at the air box. The oil was at the intake side of the throttle body. But I will take a look at the MAF.


vegask said:
This is a tool worth having. https://www.amazon.com/dp/B0BGB41DLK?th=1

Without it, I would have not known about the vac port on the bottom of the throttle body.
Click to expand...

I have hosed the outside of the engine down with starter fluid and there was no noticeable difference in how the engine ran :(

I should have my vacuum hose tomorrow and I'll yank some hoses off on Sunday. I'm hoping it as stupid and simple as hoses. :emb:
 
**** the starter fluid test....get your scanner back on it and watch live data....start removing/clamping sources of a possible vacuum leak, when you find it...you'll see it in the live data.

Check your intake boot between the air box (MAF) and the throttle body. Move it around and check for cracks in the bellows...they like to split there.
 
Lbhsbz said:
So pull the clamp and tape the **** out of it.
Click to expand...
Here is busted intake hose... not easy tape job:
CrackedIntake_sml.jpg

This is on intake side. It was cheaper to find a China one of ebay that arrived in three days for $29 :emb:

Sadly, that didn't help the situation at all. Still 1200rpm cold idle and 1600rpm hot idle:mad3:

Here is front of engine bay(red circles are not replaced yet):
HoseTop_sml.jpg

Here is side view(again, red circles are not replaced yet):
HoseSide_sml.jpg


The not replaced lines are:
  • vent line on side of the engine (side view item)
  • brake booster vacuum line
  • two super small lines along the back of the intake
  • 8mm small stub (top view mid picture circled)
  • IAC vacuum line
All the lines in question looked lightly hardened but not cracked and at least the booster & IAC hoses were still pliant.

The booster hose is not available and isn't 8mm... I haven't tried 10mm that is on the shelf yet.

Not sure on the IAC line.
 
Lil'John said:
Here is busted intake hose... not easy tape job:
CrackedIntake_sml.jpg

This is on intake side. It was cheaper to find a China one of ebay that arrived in three days for $29 :emb:

Sadly, that didn't help the situation at all. Still 1200rpm cold idle and 1600rpm hot idle:mad3:

Here is front of engine bay(red circles are not replaced yet):
HoseTop_sml.jpg

Here is side view(again, red circles are not replaced yet):
HoseSide_sml.jpg


The not replaced lines are:
  • vent line on side of the engine (side view item)
  • brake booster vacuum line
  • two super small lines along the back of the intake
  • 8mm small stub (top view mid picture circled)
  • IAC vacuum line
All the lines in question looked lightly hardened but not cracked and at least the booster & IAC hoses were still pliant.

The booster hose is not available and isn't 8mm... I haven't tried 10mm that is on the shelf yet.

Not sure on the IAC line.
Click to expand...
Might need some time to relearn. Go back to your live data....what do the fuel trims look like under the same conditions as last time?
 
To expand on that.....the ECM "learns" baseline values as time goes on and engines and components wear. Something with 200K miles on it will need slightly different IAC settings, timing, etc to idle properly....for example. After making a change, it takes a bit for the ECM to relearn those baseline settings.

I bought a 2003 4runner awhile back with a busted sub chain between the cams on one bank. Got 'er cheap :bounce2:

Anyway, after I went through the whole engine.....replaced all the bearings, rings, pistons, timing set....it was as close to perfect as one could get it....everything within OE spec, etc. Everything scrubbed inside and out, tested the VVT and it reacted how it was supposed to....the POS would die every time I came to a stop in gear for about the first 60 miles. Then it learned that it had a not-****ed-up engine in it and started acting right.

Live data will tell the story. If you're fuel trims are less than 5% or so now, while they used to be 10+.....just drive it for a bit, it'll straighten itself up
 
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