taller1

I have spent the past week trying to diagnose this idle issue to no avail.

I have the 3VZE on a 94 4Runner with about 280k miles. When it is running the idle drops to about 400-500 RPM. If I disconnect the TPS sensor, the idle jumps up to 1000. The TPS sensor has already been replaced and has been adjusted properly. I have checked this about 20 times!

I unplugged the ECM and took the OHM readings of the TPS. This was to ensure the signal is getting through the wire harness correctly.

All my vacuum lines have been double and triple checked.

OEM air box is installed.

Coolant Temp sensor was also replaced, and coolant is full.
MAF sensor was replaced.

Any ideas? I am at my wits end with this engine.

snowshredder555

Maybe IAC? Or throttle body gasket? When you replaced the coolant temperature sending unit and filled it back up, did you burp the cooling system?

taller1

I pulled the old sensor out and put the new one in right away. Coolant was flowing out, there should be no air bubbles in there.

Where is the IAC on this thing? I have never found one. Throttle body gasket is good.

justin_4runner

what does it idle when u first start it? and does it always sit at that low of a idle? might just need to turn up the idle a little.

Gamefreakgc

Common issue with this engine, complicated solution. Every situation is unique though.

Let's start with the simplest issues and work our way up. Some of these might seem obvious and you may have already done them.

1. Have you adjusted the idle speed screw on the throttle body? Idle RPM should be at 800 +/- 50 (adjust when engine is hot). After adjusting and drive testing, does it stay at 800 or does it bounce around, sometimes at 600, then 800, etc.?

2. Check all vacuum hosing for leaks. Take a can of carb cleaner and spray on all vacuum hoses and around the air intake when the engine is running (not below the Volume Air Flow Meter though). If you notice a change in idle speed, you have a leak. Replace the hosing.

3. Confirm all vacuum hoses are connected properly. Refer to the link below. Hoses connected improperly can cause low idle and low power.
http://personal.utulsa.edu/~nathan-b...74layoutan.pdf. I know you said you checked so if you used this chart already you can disregard this one.

4. I know you said your TPS is new but I had an issue with an off-brand one. Autozone sells DENSO TPS's, they are the best. My cheap one broke in three days. Also, I'm assuming you checked it per the FSM but if not here's the link: http://personal.utulsa.edu/~nathan-b...93throttle.pdf.

5. Check your fuel filter. It's located along the fuel lines between your tank and engine (in a small box). If it's dirty, replace. This could limit fuel supply causing it to idle low.

6. Check your computer for codes. Use a paperclip to jump TE1 and E1 with the engine off. Then turn to ON but don't start the engine. If there's an issue it will flash a code, just count the number of blinks. If it's fine it'll just turn on and off.

These are the easiest solutions. I would recommend not buying any more parts. The VAFM doesn't usually go bad and I'm guessing that one was pricey. Find the issue first, then replace.

orbital02

My dad's 3.0 is having a VERY similar issue... the idle constantly jumps! It doesn't throw any codes, and it drives fine other than the idle.

Gamefreak: I like your carb cleaner idea! Going to try it this weekend..

Co_94_PU

iTrader: (-1)

Pull the intake hose at the throttle, you want to inspect the throttle plate for gunk/exhaust build up. It should be very clean, not oily greasey black. If it's dirty it indicates the PAIR system has malfunctioned (One way flaps broken or cloged open) and is allowing exhaust gases into the intake. Aside from getting things dirty, it also reduces performance like having a stuck open or other leak in the EGR system. You'll need to repair or replace the PAIR valve and clean the throttle body air passages.

Clean or replace the air filter, pull the idle air screw all the way out and inspect the O-ring, screw it all the way back in then back it out one full turn. Now hook up your tachometer and adjust the idle to spec 800rpm, check/set the timing, check and adjust the idle screw again if needed and then the ignition timing again if you need to move the idle screw. What you are looking for on the idle air screws O-ring is that it's firm and plump and hasn't shrunken allowing it to turn of its own free will. There might be a spring in there that helps with this also but I don't recall currently.

*EDIT* Oops, I ment to start out saying that sounds about right for a properly working TPS, you can simulate the same effect by barely cracking the throttle (eg inserting the 0.85mm feeler gauge at the stop screw). Which opens the IDL-E2 switch

orbital02

Co_94_PU: You realize you can't check/set the timing if the idle is still jumping...

Co_94_PU

iTrader: (-1)

He didn't say it was jumping he said it was low, atleast thats how I read it "drops to about" != "bounces around"

So yeah check and repair/disable the PAIR, clean the crap out of the filter and intake then verify the idle and timing adjustments.

taller1

Thanks for all of your replies! I will be working through this list and checking everything again. I will post an update later this evening.

Co_94_PU

iTrader: (-1)

Just a quick note(s)

Vacuum leaks generally cause higher idle and lean codes, can't think of any that would cause a low idle off hand.

A cloged fuel filter will cause a lean situtation also due to low fuel pressure at the rail(s), disconnecting the Idle sensor will add more fuel.

Basicly you can probably skip over #2 and #4, and jump straight to #5 if the idle screw doesn't seem to have any effect.

Gamefreakgc

I'm yet to fully check my EGR and PAIR reed valves so they are still new to me. My TB gunked up bad when I got it, probably never cleaned before. Ever since then it's sparkling clean. I would think the LH valve cover hose to air cleaner (accordion) hose could also contribute to this since it could allow trace amount of oil to transfer from the valves to the TB. If it were the PAIR valve, I'm guessing the buildup would return even after cleaning?

I realize this was never answered. It's inside your VAFM, it's the white/yellow cylindrical object that is right in the middle of the sensor. You can test if it's working via the FSM, I believe it's the TE2 and THA terminals.

taller1

GameFreak - from your list here is where I stand:

1. The idle speed screw does make a difference, however I almost have it all the way out and it won't go over 700.

2. I get a change in RPM when I spray some starting fluid down by all the vacuum lines on the passenger side of the engine. I am going to go through all the lines and see if any are cracked. But they all look fine with the visual inspection so far. I will take each one off and test it later tonight.

3. All the vacuum lines are routed properly per the diagram on the underside of the hood.

4. I used a Beck-Arnley TPS from rockauto. It has been checked per FSM and everything is within specs.

5. The fuel filter was replaced about 6 months ago.

6. There are no codes in the computer at this time.

Co_94_PU

iTrader: (-1)

From the 22re TB removal.
Pretty sure it's the same hose in a different location for the v6's. and it's likely on the front side of the plate in my 22re too. Probably the better place to look for gunk would be the AFM exit pipe, to know whats coming from where. There is of course whole test proceedures for the PAIR and PCV systems.

PAIR gunk is dryer than PCV gunk, one is exhaust the other oil.

taller1

Correct me if I am wrong, but the typical operation of an IAC is a solenoid or motor that opens up to allow more air into the intake. Thus changing the idle speed. How can this be inside the VAFM? I looked inside and I cannot find anything that looks like that.

I am going to test the VAFM meter per FSM. Even though it has already been replaced there is always the chance I got a bad one.

Gamefreakgc

1. is not right, you've got an issue. I can raise mine up to 1500+RPM. Now the problem is isolating the issue.

2. means you have a leak. Is the jump significant? Check the hoses where they connect to the Air Intake Chamber as well as the VSV's (electronic switches on the passenger side). Try getting a 3 foot piece of hose and place one end on/in your ear and "search" with the other end. Listen for a whistle or high-pitched whine. Check the hoses as well as your cold start injector gasket, EGR gasket and near the PAIR reed valve. These could also be leaking.

I'm doubtful that the leak would cause the massive drop in RPM's you are experiencing though, sounds like to me there's more going on. No codes is good though, if you got a code 25 we would be having a grand 'ol time. However on my truck, I didn't have a code 25 because I had SO MANY LEAKS it didn't register. As I begun to fix things on the truck to where they should have been, the code appeared. Hopefully that's not the case for you.

About the IAT: That would make sense but Toyota designed their VAFM differently. The IAT is most definitely inside the VAFM, I've confirmed it when I cleaned out mine. Also, the fact that when testing the VAFM per the FSM, the connections THA and TE2 change based off temperature (different readings from the IAT) shows that it is all one unit.

Just a thought... is the top of your VAFM tampered with (i.e. not sealed, fresh sealant)? Has it ever been opened?

taller1

For some reason I was thinking of the IAC, not the IAT. The IAT is definitely in the VAFM. It has not been opened up, and I replaced it about 1 month ago with a reman unit.

I found a vacuum leak at the EGR valve where it goes into the intake plenum. That has been corrected and the is idle is better, but it is still weird.

The idle won't stay consistent. Once the engine is warmed up and I snap the throttle, it will go to 800 then creep up slowly to around 1100. Then othertimes when I snap the throttle the idle will drop to about 400. Othertimes it will go to 1100 and hang around there.

It is failing smog because of the idle, as well as high HC and CO numbers. The O numbers are good (about .1). The NO are super low. I have a feeling the erratic idle and failing smog are related.

Gamefreakgc

Looks like you and I were talking about apples and oranges. I guess I should double check before I post!

Yes, they are related. If your emissions control system isn't working right it won't pass smog. That's why they had to put all those silly contraptions on it in the first place.

Based off what you said, here's what each systems does in order to help you pass smog:

PCV valve (located on LH valve cover, a PAIN to get to): reduces HC
EVAP system: reduces HC
EGR: reduces NOx
PAIR: reduces HC and CO
Catalytic converter: reduces HC, CO and NOx

I linked each system to the FSM hope this helps ya narrow it down, like I said I don't have a whole lot of experience with these systems. Perform the check outlines by the FSM, most are very simple to do except for the PCV valve, it's a pain like I said before. Based off what the manual says, looks like the PAIR reed valve, EVAP system and PCV valve/hoses are most likely to be your culprit. If it were the cat, you'd be failing in all three emissions.

taller1

Ya, smog is a pain in the ass. I have the FSM, thanks for your links anyway, and I have checked and/or replaced every component you listed except for the EVAP. I will go through the diag on that.