3rd Gen “hunting” for idle between 1000-1500 revs

[Ellis Precision]

Wondering if anyone else has had this issue?

When I take my 3.4L 5 speed out of gear to coast on the brake up to a red light, it hunts for idle between 1000-1500 revs, and then will settle with a ridiculously high idle of 1500-2100 rpm.

To make this more clear, it revs from 1000-1500 repeatedly, back and forth.

I’ve had high idle problems before, but in both instances I was able to fix them using the washer method to remove the slop and stop the throttle plate from sticking open, then more recently I had a bad IAC so I gave the throttle a good cleaning and replaced the IAC (about a year ago).

From what I’ve read, I suspect the TPS is worn out near idle and providing an incorrect voltage to the ECU. I ordered a new Denso TPS to see if that helps. My other theory is the coolant temperature sender... I’ve checked the coolant system, it is full and burped.

I’ll keep tinkering with it until I’ve fixed it, but I’m sure someone here has seen this issue before. I’ve had a lot of people tell me I have vacuum leaks but I have replaced many of the vacuum lines already and certainly can’t find any.

Undoubtedly, someone is going to say it’s my IAC or a stuck throttle plate... it’s not! Lol

Thoughts?

Thanks in advance

 

[gamefreakgc]

The TPS is insanely hard to align correctly. If the factory paint marks are still there, I would not recommend removing the old one until you have no other option.

Normally it's easier just to replace the entire throttle body.

EDIT: Had a thought, is the dashpot (if it has one) or the screw propping the throttle valve open? I know you said it's not stuck, but it may also not be closing all the way.

 

[Ellis Precision]

Still, the throttle plate not closing would not make the ecu hunt for the idle speed.

Have you replaced a TPS? Replacing the entire throttle over a TPS seems insane to me.

As far as I know, you need feeler gages and a multi-meter to correctly align a new TPS. What am I missing?

 

[t4r-428]

Are you sure it's not just your A/C kicking on and off. My 4runner does the same thing. So I got out one day and listened to it and I heard the A/C clutch engaging and disengaging. So I believe that's what is was.

Sent from my XT1650 using Tapatalk

 

[thecole1098]

Still, the throttle plate not closing would not make the ecu hunt for the idle speed.

Have you replaced a TPS? Replacing the entire throttle over a TPS seems insane to me.

As far as I know, you need feeler gages and a multi-meter to correctly align a new TPS. What am I missing?

I've replaced TPS before and it seemed to work fine for me by just simply swapping them out. The older 3.0s required "tuning" of it but not these 5VZFEs.

Are you sure it's not just your A/C kicking on and off. My 4runner does the same thing. So I got out one day and listened to it and I heard the A/C clutch engaging and disengaging. So I believe that's what is was.

Sent from my XT1650 using Tapatalk

No, the AC kicking on and off should not cause that drastic of a RPM change. And if it happened to be kicking on and off as fast as I think the OP is describing, there is an issue in the AC system.

 

[96RedRunner]

You don't mention what year you have, The 96-00 have a simpler throttle
system than 01-02 is why I ask. I had problems like yours after a valve cover
gasket job. The grounding bundle that attaches to intake plenum (at diagnotic port) was loose. That particular ground is critical for engine management.
Something to check, corrosion on ground could cause same issue I would think.
Since your in the rust belt.

 

[gamefreakgc]

Still, the throttle plate not closing would not make the ecu hunt for the idle speed.

Have you replaced a TPS? Replacing the entire throttle over a TPS seems insane to me.

As far as I know, you need feeler gages and a multi-meter to correctly align a new TPS. What am I missing?

If you're game, then by all means go for it. It's too daunting for your averager DIY'er on here, but if you have the patience and tools then you should be good. I owned a 3.0L and it was as simple as put on new sensor, start truck, rotate to desired idle/throttle opening and done. These, not so much.

You don't mention what year you have, The 96-00 have a simpler throttle
system than 01-02 is why I ask. I had problems like yours after a valve cover
gasket job. The grounding bundle that attaches to intake plenum (at diagnotic port) was loose. That particular ground is critical for engine management.
Something to check, corrosion on ground could cause same issue I would think.
Since your in the rust belt.

He has a manual so it's a 96-00, so doesn't have to mess by the drive by wire throttle on the 01-02's.

 

[nobb]

Did you clean or take apart the throttle body/IAC recently? The throttle plate position is very finicky, but the ECU does over time re-learn to compensate for wear. I had a similar problem after cleaning the IAC and ended up having to put a small spring on the throttle body to force it to close a bit tighter. A few months later I was able to remove the spring as the ECU seemed to have magically re-learned the positions.

 

[Ellis Precision]

Are you sure it's not just your A/C kicking on and off. My 4runner does the same thing. So I got out one day and listened to it and I heard the A/C clutch engaging and disengaging. So I believe that's what is was.

Sent from my XT1650 using Tapatalk

No, that’s not it. I know the 5VZFE better than most and I know it will idle higher when the AC clutch is engaged, but that’s not what is at play here.

I bought the truck without AC and installed it myself, just to give you an idea of how familiar I am with the system.

It’s also stupid cold here right now and I have the AC turned off.

 

[Ellis Precision]

I've replaced TPS before and it seemed to work fine for me by just simply swapping them out. The older 3.0s required "tuning" of it but not these 5VZFEs.



No, the AC kicking on and off should not cause that drastic of a RPM change. And if it happened to be kicking on and off as fast as I think the OP is describing, there is an issue in the AC system.

Exactly.

I just had a good look at the TPS... it is not tuneable like the previous model Toyota’s I have worked on. Many are slotted for adjustment with feeler gages and there is a resistance to set based on a small gap between a closed and cracked open throttle plate.

This one looks like a straight replacement.

I have no idea what the previous comment about replacing the entire throttle body was about, but I’ll replace the TPS in accordance with the factory service manual.

 

[Ellis Precision]

If you're game, then by all means go for it. It's too daunting for your averager DIY'er on here, but if you have the patience and tools then you should be good. I owned a 3.0L and it was as simple as put on new sensor, start truck, rotate to desired idle/throttle opening and done. These, not so much.



He has a manual so it's a 96-00, so doesn't have to mess by the drive by wire throttle on the 01-02's.

I think you are referring to the accelerator position sensor, instead of the throttle position sensor.

I agree the Throttle Body basically has to be replaced if it's the accelerator sensor that has gone bad. I will know soon.

I actually have a spare throttle body (entire engine and supercharger actually) so either way I will have this fixed shortly.

 

[gamefreakgc]

I think you are referring to the accelerator position sensor, instead of the throttle position sensor.

I agree the Throttle Body basically has to be replaced if it's the accelerator sensor that has gone bad. I will know soon.

I actually have a spare throttle body (entire engine and supercharger actually) so either way I will have this fixed shortly.

So wait... you have a Supercharger just laying around??? Slap that baby on there! Works just fine on a stock engine and you'll love it.

Good luck on the fix though!

 

[thecole1098]

I'll take the supercharger off your hands if you have no intention on using it

 

[Ellis Precision]

So wait... you have a Supercharger just laying around??? Slap that baby on there! Works just fine on a stock engine and you'll love it.

Good luck on the fix though!

I have 530k+ on my current engine... not really willing to risk it. The engine it is sitting on has nearly half that, but I don't really feel like doing an engine swap this year. LOL

I pull wrenches when I have to, but I have other things I'd rather be doing at this stage in my life.

I've heard there can be some air/fuel ratio issues and detonation I don't really want to deal with...

I'll take the supercharger off your hands if you have no intention on using it

I like having the option. I paid $1200 for it, but it was $1200 I didn't really need so for now it can sit on the engine on the hoist. :wink2:

 

[thecole1098]

Is it the Gen1 (gray) or Gen2 (black)?

 

[Ellis Precision]

Is it the Gen1 (gray) or Gen2 (black)?

Its a gen2.

 

[Ellis Precision]

So I chucked more parts at this problem and still have the problem.

I still occasionally get P0505, but my idle air control valve is practically brand new and clean.

I did replace the TPS, and I get 9 on my scanguage at idle and 74, so according to the FSM those are in range.

I have checked and cleaned the PCV valve as well, since I have heard this can also cause this. It seemed fine the whole time, but I have another one on the way just incase (they are super cheap).

Checked again for vacuum leaks, can't find any!

Two new facts:

Unplugging the IAC drops the idle right within the specs of 700+-50 (accessories off)

If I drive the 'Runner until it is at operating temp (approx 191 F on my scan gauge), then park it for 20 minutes or so, when I come back out it starts and idles at a perfect 700 rpm. Heatsoak maybe helping something out? THis is probably the most frustating thing... the throttle body isn't worn out and the truck CAN idle properly, it mostly chooses not to. LOL

Next up:

I'm going to remove the IAC and swap it for a brand new factory one. The current one is aftermarket. I don't see this making a difference but was reading that the IAC does have a thermistor in it... it is getting a signal from the ECU to open and let my engine idle high but apparently it DOES provide feedback.

I'm going to replace the ECT probe. There are 2... one is a sender, one works for the ECU. The sender one provides info to my Scanguage and dash. I'm going to replace the ECU one on the front passenger head because it's easy to do and also super cheap.

I don't know when the last time the previous owner did O2 sensors, so I'm going to do both upstream and downstream sensors with Denso from Rockauto.

PCV valve will be replaced as well. And of course, I'll remove the negative terminal while I do all this and reset my clock and alllllll my presets on the stereo but maybe the pissed off ECU will re-learn how to idle!

 

[endgame56]

So I chucked more parts at this problem and still have the problem.

I still occasionally get P0505, but my idle air control valve is practically brand new and clean.

I did replace the TPS, and I get 9 on my scanguage at idle and 74, so according to the FSM those are in range.

I have checked and cleaned the PCV valve as well, since I have heard this can also cause this. It seemed fine the whole time, but I have another one on the way just incase (they are super cheap).

Checked again for vacuum leaks, can't find any!

Two new facts:

Unplugging the IAC drops the idle right within the specs of 700+-50 (accessories off)

If I drive the 'Runner until it is at operating temp (approx 191 F on my scan gauge), then park it for 20 minutes or so, when I come back out it starts and idles at a perfect 700 rpm. Heatsoak maybe helping something out? THis is probably the most frustating thing... the throttle body isn't worn out and the truck CAN idle properly, it mostly chooses not to. LOL

Next up:

I'm going to remove the IAC and swap it for a brand new factory one. The current one is aftermarket. I don't see this making a difference but was reading that the IAC does have a thermistor in it... it is getting a signal from the ECU to open and let my engine idle high but apparently it DOES provide feedback.

I'm going to replace the ECT probe. There are 2... one is a sender, one works for the ECU. The sender one provides info to my Scanguage and dash. I'm going to replace the ECU one on the front passenger head because it's easy to do and also super cheap.

I don't know when the last time the previous owner did O2 sensors, so I'm going to do both upstream and downstream sensors with Denso from Rockauto.

PCV valve will be replaced as well. And of course, I'll remove the negative terminal while I do all this and reset my clock and alllllll my presets on the stereo but maybe the pissed off ECU will re-learn how to idle!

Found this hunting through google and was wondering if you ever found fix?

I've been dealing with this exact issue for the better part of a year now, and it doesn't really affect much other than my sanity, but I have to do the timing belt soon and figured I may as well take another stab at this.

 

[Ellis Precision]

Found this hunting through google and was wondering if you ever found fix?

I've been dealing with this exact issue for the better part of a year now, and it doesn't really affect much other than my sanity, but I have to do the timing belt soon and figured I may as well take another stab at this.

I've replaced pretty much everything... still does it, but only when cold ambient temps lol

New IAC (expensive OEM), new OEM O2's, new PCV, did the valve cover gaskets and intake/throttle body/all related gaskets and cam plugs/half moons (unrelated), new timing belt, new water pump, new thermostat, new heater core in the rear... I maintain the sh!t out of this thing but can not figure out this cold high idle. New MAF, plus more.

The throttle body is closing correctly. The IAC is getting some sort of signal to stay open when it is cold outside.

My next step is the under hood insulation... hoping that traps some of the heat in the winter under the hood... $500 though so I'm saving pennies and hope to have one by January when it gets REALLY cold.