Dude Man

I've owned my 4Runner for nearly a year now and for the most part the truck is solid and runs fine. But there's a few quirks that have been bugging me for some time and I'd like to try and finally deal with them.

1. A hesitation/misfire/overall lack of power when cold.

Usually in the morning on the way to work or in the afternoon on the way home from work, so after its been sitting a fair amount of time.

So every morning when I leave I have to let the clutch out very slowly and rev it much harder than usual or it will stall.

Then, once I'm on the road it falls flat on its face between shifts. I shift at 3 grand or just under so I'm not bogging it or anything. The RPM seems to fall really fast when I depress the clutch and it makes for some ugly shifts the first few minutes on the road.

When I'm in gear and accelerating the truck feels very underpowered and I have to give it more gas than usual.

All of these symptoms slowly go away as it warms up and once its at NOT its fine.


2. High idle while cold/low, crappy idle when warm.

I've noticed the idle-up when its cold is a bit high, going up to 2 grand when its really cold sometimes, usually 1500 even if its warm out. Rarely, maybe once a month, the RPM will start surging between 1500 and 2000. If I tap the throttle it stops doing this and the idle slowly goes down.

The only upside to this high idle is it helps get the truck moving (see problem 1.)

Once the engine is at NOT the idle is very unpredictable. Most of the time when I pull up to a red light or stop the idle will be low and the truck feels like its running rough, about 500-600 RPM. If I tap the throttle it kicks up to 900-1000 and stays there, until the next red light/stop where it goes back down. Sometimes I stop and the idle is spot on where it should be at 850, sometimes its already high though I haven't jabbed the throttle.

Pushing the break pedal in all the way makes it idle higher sometimes, I used to do this but now I just jab the gas pedal.

Disconnecting the TPS made no difference, I still have to test it.


3. There's never coolant in the top of the radiator.

This scared me at first. I bought the truck, found this site, discovered the 3.0's common issues and then saw the rad was empty.

But after driving it nearly a year I'm fairly certain the HG's fine.

I replaced the rad cap, topped up the rad/overflow bottle and it stayed full for a while but recently I checked it and the top part is empty again. Overflow is at the same level and oil is fine so its not ingesting the coolant or anything.

Not too concerned about this one yet. I'd like to flush the entire coolant system and get some Toyota Red in there. I have a feeling this is related to the trucks heater taking forever to get warm, even though the engine reaches NOT at a normal rate.


This is everything I've done so far;

-Replaced dizzy cap, rotor, wires and plugs.
-Changed all drivetrain fluids with synthetic.
-Cleaned throttle body, AFM.
-Replaced rad cap.
-Replaced 02 sensor with NTK/NGK unit.


Things I would like to do;

-Compression test.
-Check timing.
-Check TPS.
-Replace cat with straight pipe.
-Coolant flush.
-Replace spark plugs again.


Any advice would be appreciated. I've been putting these issues off for a long while now so I haven't really done much to figure them out but I figured I'd make a thread and get a few more perspectives and keep track of my progress.

Here's a pic of my rig, cause everyone likes pictures

thook

First, I want to compliment you on your clear post. Very well delineated. Makes it very easy to understand.

Second, test the throttle sensor. Usually, if there's no change by disconnecting it, that indicates the TPS is atleast part of if not the entire problem. I mean, with the age of the vehicle, there could be more than one thing going on. Just have to eliminate things one by one.

Get the leak fixed. That could cause the same problem or atleast exacerbate the underlying issue.

Here's a troubleshooting chart:
http://personal.utulsa.edu/~nathan-b...63troubles.pdf

TNRabbit

If you have coolant going away, I'd add a coolant system pressure check to your list of to do's. you can get a kit from Sears cheap. It will tell you things the compression check may not...

dr1553

My 91 3.0 has been having the same issues for about a year now. It ran smooth when I got it and then one day it started to idle rough. Mine has the same issues you talk about, high idle at startup, low idle at stoplights when warm, no power, shuttering during acceleration, falls flat between shifts...all that.

I checked the TPS a year or so ago....I believe it tested fine but I'm not sure now if I tested it correctly. Been too long ago.

I changed the cat recently and it was like night and day! The truck ran perfect, idled great, power under acceleration....for about two weeks. Then right back to like before. Now its running worse than ever. It just passed inspection last week, the only thing was a bit high reading on low speed nox. Inspector recomended checking the EGR valve.

Do a few searches for TPS and you will find a dozen posts with guys listing all the same problems that you and I are having. The thing I dont find in my searches is a cure for the problem.

Seems most peoples advise is to check the TPS and the coolant temp sensor. I dont know where the coolant temp sensor is or how to check it.

Oreilly sells two different brands of TPS, one for $85 and the other for $140, I dont know the difference between the two. I'm about ready to spend the money on a new one just to eliminate it as a possible problem. But isnt there some setup to get the new one working correctly?

Isnt there also another part that manages the air/fuel ratio? The thing with the trap door that tells how much air is being fed to the engine?

With all the people having the exact same issues with their 3.0 someone has to know how to fix it. I dont think its just "how they are", they didnt run like this when they were new. I wonder if the stealership might be able to fix it. Maybe they have seen the issue enough times and know the problem by now.

Dude Man

The cheaper TPS might be a universal part, which you should generally stay away from.

The trap door unit is the AFM. I've actually swapped mine with one from a 3SGTE but it hasn't really made a difference so I'll probly put the stock one back on.

If you buy a new TPS it has to be set when you install it. I believe you can rotate it like the dizzy cap or something but I'm not completely sure.

Haven't had a chance to check mine yet since I need to buy one of those little volt-meter things and its been an unusually cold September. I'll update this thread when I do.

warmonger88

wow, i'm having the same troubles with my 94. it's becoming really bothersome too. is there any brand suggestions for the tps?

Dude Man

I would suggest OEM, personally.

You might as well test the one you have now though since you will have to set the new one when you install it.

chad500

The rough idle when cold could be a broken or malfunctioning bi-metal switching valve, located at the back of the intake beside the water temp sensor, and the water temp switch. Everybody that even looks at that vacuum switch breaks it, ask me how I know. That vac switch controls the EGR valve, which should remain closed when cold. People bypass that part when they break it, opening the EGR as soon as the engine is running, which will cause it to run rough until warm. With the engine cold, unplug the EGR valve and see if it runs better, and also check to see if there is vacuum at the hose you removed from the EGR. I'm not a mechanic but I did stay at a Holiday Inn Express last night.

Dude Man

^Engine runs fine when cold, just idles higher than it should.

The rough idle starts once the engine is warm.

I'd like to delete my entire EGR system eventually.

warmonger88

i hear that!

theMonch

Dude Man, I chased this exact problem down for over a year. I tryed everything simple, plugs, wires, dist cap,etc, etc, etc. The problem will eventually creep in to normal operating temperature driving in the form of a slight hesitation at lower load highway driving.

Finally even though it had tested out fine according to the FSM, I replaced the VAF (vane air flow meter). Voila!!

What happens is the VAF gets a worn spot in the potentiometer that sends air flow readings to the ECM. This is most common in manual trans trucks from the research that I had done.

You can pick up a used factory toyota piece on eBay for 60-75 bucks. (thats what I did)

If the part number on it is 22250 65010, then I have the one I used to fix the problem for me available for $50 plus shipping. I just swapped a 5VZ into my truck and no longer need it.

Dude Man

^Good thinking, AFM is a definite culprit.

Unfortunately I've already swapped the AFM with the one from my 3SGTE and it made no difference.

dr1553

That first sentence describes my truck exactly, it slowly crept into normal operating temp so now I have hesitation/surging at all times now. When I am driving at a steady speed the power increases and decreases on its own without moving the gas pedal. Also at idle I can feel/hear something click and the idle will increase from 400-500 up to 850 for a few seconds then fall back to a very rough 400-500.

What/where is the VAF? Is that the same thing that Dude is refering to as the AFM?

If yours will work in my truck and my problems sound like what you had then I will take it off your hands.

thook

The airflow meter sits on top of your air filter box. It has a seven pin connector going to it. Here's the procedure for testing it:

http://personal.utulsa.edu/~nathan-b...92volumeai.pdf

However, it can pass the test given in the manual and still be defective. Read this:
https://www.yotatech.com/forums/f116...esting-146662/

A simple, quick test on the TPS is to disconnect it. If the condition improves or clears entirely, this can only mean the sensor is faulty on or more of the circuits and is interfering with normal operation by giving erroneous feedback. Example; telling the ECU the throttle is wide open when it's not. By disconnecting, the ECU will go into a default mode where it operates the EFI system utilizing other major sensor input fairly well. However, if the condition doesn't change, it's something else. In which case, it could be the airflow meter or the coolant sensor.

The coolant sensor is located on the very back of the intake manifold. Should have a grey connector.....second sensor from the right. Here's the procedure for testing:
http://personal.utulsa.edu/~nathan-b...98engineco.pdf

When the coolant is below a certain temp (when the engine's cold), the resistance should be high. As it heats up, the resistance should drop. When resistance is high, voltage is high signaling the ECU the temp is low. Vice versa when the motor is hot. Specifications on resistance are not so important as noting a steady decrease in resistance. I mean, the readings should be atleast close to the parameters given in the manual, but don't worry if it's a few ohms off given a specific temperature.

dr1553

Good stuff!!! I'm going to test my AFM using your sweep technique. The thing is running like the air/fuel mix is off so that would be the place to check huh. That and I will try unplugging the TPS also. Do you unplug it while its running?

Maybe I will just install a mix knob like in airplanes.

thook

Are you serious about that knob?

I'll just say the AFM is a good place to start. There are several components that affect the a/f ratio. The AFM is one of the major components, if not the most. Each component has it's "distinct" symptoms when they start malfunctioning, but they can also display similar ones. That's why the FSM guide usually gives the mechanic a few possibilities. When you get familiar enough with the distinctions or specifics of each one, though, you can many times make accurate guesses before even testing. Sometimes there can be more than one thing going on, and sometimes one can be wrong by their guessing, so that's why you test. And, it's a good rule of thumb not to jump to definite conclusions right away. Then, you go replacing parts and spending time and money unnecessarily.

dr1553

No...I'm not serious about the mix knob. Just an overly simple (silly) way to fix all the air/fuel ratio problems these things seem to have. Of course it wouldnt work.

It's weird how my truck acts, yesterday it was running so bad it felt like there was water in the fuel.....today it ran fine(relatively). Not as well as it should but it wasnt surging and then dropping out while driving at a steady speed.

To check the TPS simply unplug it while at running idle? I can do that when its doing its 450-500rpm rough idle and see if it makes it idle smoother huh? Does it hurt anything to leave it unpluged until I get a new one or fix the old one if unplugging it seems to help? The way you describe it the TPS is just a way to help fine tune the A/F mix right?





To the OP.....are you sure the AFM you swaped into your truck was a good one?

wii_tarded

I have a problem with my 3.0.....



It jumped out of my truck. If you need any parts, let me know via pm or else I'll forget this tread. I am gonna start parting out my 3.0.

theMonch

Mine was exactly like this. That is why it took so long to diagnose. One day everything is fine, then the next it's back. I used to think it was temp related and actually started carrying around a log of baro pressure and temp for each day/occurance to try and pinpoint a pattern.

thook

Yeah, it can be difficult to pinpoint a problem with a component that's not so temp dependent because the a/f changes according to temp and this, of course, affects how the engine runs whether or not there's even a problem.