A seemingly impossible to diagnose 3rd Gen issue

A

appst8

New member
I have had an issue with my truck for the past 3 years that has stumped myself and two other "Toyota Specialists" in the area. Bestow upon me me your 4Runner expertise so I can fix this problem!

The Car: 99 T4R SR5 4x4 5VZ-FE

The Issue: ONLY on hot days (80 F and above) when stopped (both in drive or park) the car will suddenly begin to idle a bit rough and then suddenly stall. Without fail, I can start the car immediately afterwards and keep driving like nothing ever happened. Usually when the idle becomes lower and rough, I can give it a bit of gas and things return to normal. When this happens, the car dosen't throw any kind of CEL. Keep in mind, when the temperature is colder than 80F, it runs perfectly. No issues.

The "fixes" so far: Since my workhorse has over 250K on the clock, I have replaced a few old, dry vacuum lines in case they were cracked. Since I do not have the time or space to work on her these days, I took it to a mechanic who cleaned the IACV. I thought this fixed it for a month or so, but the problem resurfaced. Another mechanic looked it over, and told me to continue driving it until it throws a code.

Parts Replaced Recently: All belts, TPS, Plugs, Wires and One Coil Pack.

Please give me any tips you may have, this has been hugely frusterating and I would like to take care of this before warm weather returns.
 
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Can't speak with any certainty, but your IAC may need replacing rather than cleaning. Mine was stone dead (but had failed open, so the result was a high idle) with I bought it, and it wasn't throwing any codes either.

If you don't get any more promising leads from the veterans here, an OEM IAC goes for around $80 on ebay (last I looked) and is simple to replace (remove throttle body, replace IAC, takes about an hour with minimal tools.)
 
0xfded said:
Can't speak with any certainty, but your IAC may need replacing rather than cleaning. Mine was stone dead (but had failed open, so the result was a high idle) with I bought it, and it wasn't throwing any codes either.

If you don't get any more promising leads from the veterans here, an OEM IAC goes for around $80 on ebay (last I looked) and is simple to replace (remove throttle body, replace IAC, takes about an hour with minimal tools.)
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I appreciate the input. If the IAC was bad, would the problem continue to happen even if it was cold outside? Regardless, for throwing a part at a car $80 isn't too bad.
 
My 98 does it as well. Most recently after hard throttle to idle. But mostly only did it on hot days. In for and answer as well.
 
X2 for the IAC Kinda obvious to me since you cleaned it and the problem went away. Could be a coincidence maybe. Other things you might want to check are the free movement and centeredness of the butterfly in the throttle body. Replace the fuel filter. Clean the MAF. Check the fuel pressure.
 
shootmymime said:
Could be iac, What about MAF cleaning?

It has to do something with air fuel ratios it sounds like.
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I forgot to mention I took the MAF off and gave it a good cleaning. A bit of carbon buildup on the intake side but everything else appeared to be fine.
 
The butterfly valve seems to work not stick. Any tips for checking fuel pressure before/after the fuel filter? Correct me if i'm wrong, but I thought the fuel filter was a part that shouldn't need servicing for the life of the car.
 
appst8 said:
The butterfly valve seems to work not stick. Any tips for checking fuel pressure before/after the fuel filter? Correct me if i'm wrong, but I thought the fuel filter was a part that shouldn't need servicing for the life of the car.
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Shouldn't, but every Toyota truck I've owned has needed a new one at one point or another. They tend to get clogged, faster if the truck has sat around with old gas in it for any amount of time.
 
I used the search function, but cant find any articles about checking fuel pressure. Is this a value I can see using a scan-tool or will I need to buy an analog gauge and tap into my fuel line somewhere?
 
appst8 said:
I appreciate the input. If the IAC was bad, would the problem continue to happen even if it was cold outside? Regardless, for throwing a part at a car $80 isn't too bad.
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I'm speculating now, so hopefully someone more knowledgable will correct me if I'm off base:

When your intake temps go up, the engine needs more of the hotter (less dense) air. If your IAC is not opening correctly, the engine isn't getting that air and stalls.

What gives me pause is that there's no problem starting. I don't know offhand if the IAC is controlled differently on start, but it probably is. If it's a mechanical failure (ie. IAC jammed shut), you'd have trouble starting. Which is weird.

Sounds like you've already checked your MAF. You sure you're not getting any codes, like P0505 or P0115?

Couple of similar threads here, here, and here.
 
gamefreakgc said:
Shouldn't, but every Toyota truck I've owned has needed a new one at one point or another. They tend to get clogged, faster if the truck has sat around with old gas in it for any amount of time.
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At 100K miles , a considerable amount of junk comes out of the old filter.
Maybe in Japan, the gas is like the old Smirnoff Vodka ads: "Filtered through A Mountain Of Charcoal"....but not here!
<iframe src="http://library.duke.edu/digitalcollections/embed/oaaaarchives_AAA9746/" width="625" height="565" frameborder="0" webkitallowfullscreen="true" mozallowfullscreen="true" allowfullscreen></iframe>
 
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0xfded said:
I'm speculating now, so hopefully someone more knowledgable will correct me if I'm off base:

When your intake temps go up, the engine needs more of the hotter (less dense) air. If your IAC is not opening correctly, the engine isn't getting that air and stalls.

What gives me pause is that there's no problem starting. I don't know offhand if the IAC is controlled differently on start, but it probably is. If it's a mechanical failure (ie. IAC jammed shut), you'd have trouble starting. Which is weird.

Sounds like you've already checked your MAF. You sure you're not getting any codes, like P0505 or P0115?

Couple of similar threads here, here, and here.
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My CEL is not illuminated, and does appear when starting the car as it should. Could there be codes even though it is not on?
 
I had this issue and I tried cleaning the IAC and it helped out. I also found that my battery terminals were not solid and that was causing a lot of issues. After messing with both the issue hasn't come back. I know it sounds weird but I'd adjust your battery connections and clean them up.
 
appst8 said:
My CEL is not illuminated, and does appear when starting the car as it should. Could there be codes even though it is not on?
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Yes, you could be throwing a pending code.

I had this issue; I keep a close eye on my mileage and saw it was going down though the driving done was staying the same, I also noticed an occasional rough idle but no codes so I drove it for a week and blamed it on bad gas or water in the gas, changed gas stations and drove for another week the problem persisted. One day I came home just to run in and grab something so I left the truck running, when I came back down it was dead. I was very concerned about this but it started back up and kept running, I immediately took it to a box auto store to see if it had codes that popped up and cleared but it had no active codes. After a bit of digging I had a pending code for my throttle position sensor. We started the truck and just tapped the sensor the rough idle would come and go. Went to the dealer and replaced the TPS problem solved.

I know you said you replaced the TPS but did you use OEM, also have you used a volt meter to test the sensor and make sure it's good?

With your key in acc but the engine off set your meter to read 12v DC and contact the plenum with your black lead then insert a sewing pin into the bottom of the three wires protruding from the connector for your TPS and touch your red lead to the needle, with the throttle body closed you should be under 1v (I read .57v DC) and with the throttle wide open you should read less than 5v (I read 3.67v).
 
If it keeps up I would say throw in a C reader (Code Reader II) Drive with it in until acts up again and you will be able to go back and look at that freeze frame and see all the data when it happens. That has helped us in the past.

Blue
 
appst8 said:
I have had an issue with my truck for the past 3 years that has stumped myself and two other "Toyota Specialists" in the area. Bestow upon me me your 4Runner expertise so I can fix this problem!

The Car: 99 T4R SR5 4x4 5VZ-FE

The Issue: ONLY on hot days (80 F and above) when stopped (both in drive or park) the car will suddenly begin to idle a bit rough and then suddenly stall. Without fail, I can start the car immediately afterwards and keep driving like nothing ever happened. Usually when the idle becomes lower and rough, I can give it a bit of gas and things return to normal. When this happens, the car dosen't throw any kind of CEL. Keep in mind, when the temperature is colder than 80F, it runs perfectly. No issues.

The "fixes" so far: Since my workhorse has over 250K on the clock, I have replaced a few old, dry vacuum lines in case they were cracked. Since I do not have the time or space to work on her these days, I took it to a mechanic who cleaned the IACV. I thought this fixed it for a month or so, but the problem resurfaced. Another mechanic looked it over, and told me to continue driving it until it throws a code.

Parts Replaced Recently: All belts, TPS, Plugs, Wires and One Coil Pack.

Please give me any tips you may have, this has been hugely frusterating and I would like to take care of this before warm weather returns.
Click to expand...

Let me know if you solve this problem. I have similar symptoms except mine does not idle rough before it stalls. It starts up no problems after it dies. Seems like it happens on warm days as well. Someone suggested it is my fuel pump. I'm going to replace it soon. Check out my thread.

http://www.toyota-4runner.org/3rd-gen-t4rs/188455-help-intermittent-stalling-tried-everything.html
 
If you are ABSOLUTELY sure you have no vacuum leaks, these are my best guesses.

1. Replace the fuel filter, especially if it looks original.

2. Clean the TB really well. Remove it if you feel you think it will help. Clean around the butterfly area, the IAC AND the seat, basically anywhere with carbon buildup. Might as well put on a new IAC while your at it too. Check all of the small orifices and make sure they are clear.

This is definitely a starved air/fuel type of problem. I am leaning more towards air flow problems through the TB, since it is affected by warmer weather. Warm air is less dense, so if the idle air flow has a restriction problem, it would be more pronounced in warm weather.
 
Sorry for being MIA for so long, it's awesome to get so much support form the community. And my condolences for everybody who is dealing with this headache of an issue. I think i'm going to check the voltages on my TPS, clean the throttle body and go from there.

Is there a way to make sure my IAC is working properly with my multimeter? I don't want to throw parts at it if possible.
 
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