Does this sound like Idle Air Control Valve failure?

[Robb235]

So Sunday night I had done about 3 hours of interstate driving heading home. I get off the interstate and start heading up a mountain. I'm approaching a sharp turn in the road, and when I let off the gas, the motor died completely. Luckily no one was behind me, and I was able to restart and keep going. I approached another turn, let off the gas, and the engine died once more. I restarted, and then kept one foot on the gas, and braked with my left foot.

Only thing I can think of that would cause this, is that maybe the Idle Air Control Valve isn't opening quick enough when I snap the throttle shut, and it's causing the engine to die?

Thoughts?

 

[gamefreakgc]

No, you were still moving when it died correct? That would be something else. The IAC issues are more when completely stationary, since when you are moving the engine should still be rotating to keep the engine from dying. If that's the case, there might be a fuel delivery issue going on, but a tune-up might also be in order.

If you were at a complete stop, then yes, that's the IAC.

P.S. I recently tried using a reman'd unit for cheap off Ebay (was $30) but it idled way too high. Looks like OEM is the only way to go.

 

[altoonabcm157]

I had a ford explorer that the IAC valve failed and it would only die when in park and you let your foot off the gas, if you revved gently in park it would run and after it was in drive then there were no issues. If you were in Drive it wouldn't ne IAC valve.

 

[SCRunner12]

I had this happen on my 2000 years ago. I ended up cleaning and tightening the battery terminals and cleaning the MAF, IAC and throttle body. Don't know which one did the trick but it worked fine after that.

 

[Robb235]

No, you were still moving when it died correct? That would be something else. The IAC issues are more when completely stationary, since when you are moving the engine should still be rotating to keep the engine from dying. If that's the case, there might be a fuel delivery issue going on, but a tune-up might also be in order.

If you were at a complete stop, then yes, that's the IAC.

P.S. I recently tried using a reman'd unit for cheap off Ebay (was $30) but it idled way too high. Looks like OEM is the only way to go.

Yes, I was moving, but very slowly since I was about to go around a hairpin turn.

My thought was that the IAC is still working, but the IAC motor has gotten slow due to age. So when I snapped the throttle shut, IAC didn't open fast enough, causing the engine to die due to lack of air. It died again one other time when I had immediately restarted. I had to give it gas to keep it running, and when I let off the gas (still in Park) it died again. Had to keep my foot on the gas to keep it running.

I've since tried to recreate the issue (on an empty road, no traffic) and it hasn't done it since.

 

[nc-grayson]

No, you were still moving when it died correct? That would be something else. The IAC issues are more when completely stationary, since when you are moving the engine should still be rotating to keep the engine from dying. If that's the case, there might be a fuel delivery issue going on, but a tune-up might also be in order.

If you were at a complete stop, then yes, that's the IAC.

P.S. I recently tried using a reman'd unit for cheap off Ebay (was $30) but it idled way too high. Looks like OEM is the only way to go.

not trying to throw a wrench in the mix here, but FWIW I'm over 35k on a no-name ebay IAC and I've been fine, (I did spend $59 though) - guess they're hit or miss

 

[gamefreakgc]

Yes, I was moving, but very slowly since I was about to go around a hairpin turn.

My thought was that the IAC is still working, but the IAC motor has gotten slow due to age. So when I snapped the throttle shut, IAC didn't open fast enough, causing the engine to die due to lack of air. It died again one other time when I had immediately restarted. I had to give it gas to keep it running, and when I let off the gas (still in Park) it died again. Had to keep my foot on the gas to keep it running.

I've since tried to recreate the issue (on an empty road, no traffic) and it hasn't done it since.

Try what SCRunner suggested, clean up your battery & terminals and clean the MAF first. Those are way easier than taking off the throttle body and can be done in 15 minutes for both.

MAF could cause the same condition if it stopped reading air moving, since it would cut off fuel when you still need it.

 

[Robb235]

Try what SCRunner suggested, clean up your battery & terminals and clean the MAF first. Those are way easier than taking off the throttle body and can be done in 15 minutes for both.



MAF could cause the same condition if it stopped reading air moving, since it would cut off fuel when you still need it.

It did it again coming home from work. Would die if I let of the gas a slow speed or stopped. Had to keep foot on the gas and brake with my left foot.

I haven't cleaned my MAF in a while, so I should do that. I'll check the battery terminals as well. It's just too cold outside right to do any wrenching with this arctic blast going on.


Sent from my iPhone using Tapatalk

 

[Robb235]

Cleaned my battery terminals. They're on pretty tight.

Hard to do much else when the temperature is this:

Sent from my iPhone using Tapatalk

 

[4bangr]

it's the idle control valve <- (it's right there in the name "idle control).

take it out, clean it, it might work better for a while; start looking for a new one.

 

[cbr900boy]

Check out my thread on my mysterious stalling. It took me a while including replacing a lot of parts, which wasn't a complete waste cause they needed replacing anyways. I even replaced the IAC valve, fuel filter, fuel pump, etc. Ultimately, it was the EVAP Canister. I believe your 99 is just like my 98 where the canister is located under the hood as opposed the newer models where they are located in the rear next to the spare. Anytime it comes to electronics I don't even mess around with aftermarket, everything OEM.

I knew it had to do something with stalling while at idle because when the throttle plate it completely closed i.e. foot off the gas, the air has to come from somewhere right? At this point, IAC valve was the logical answer...nope. Apparently the EVAP canister also has a series of valves which feed air past the throttle plate to keep the engine running at idle....BINGO that was the solution. My rig is 20 years old now with 270k miles, it was about due for a replacement. Something to think about.

 

[Buckaroo]

So Sunday night I had done about 3 hours of interstate driving heading home. I get off the interstate and start heading up a mountain. I'm approaching a sharp turn in the road, and when I let off the gas, the motor died completely. Luckily no one was behind me, and I was able to restart and keep going. I approached another turn, let off the gas, and the engine died once more. I restarted, and then kept one foot on the gas, and braked with my left foot.

Only thing I can think of that would cause this, is that maybe the Idle Air Control Valve isn't opening quick enough when I snap the throttle shut, and it's causing the engine to die?

Thoughts?

The IAC is the most likely culprit - it will get gummed up and not move freely which causes stalling when the engine RPM's drop. This build-up happens over time (mine occurred at 235,000 miles) but cleaning the throttle body and allowing the sludge to drip into it can bring on the problem. Got to remove it to clean properly - be careful not to cam-out/hose up the screws - they are tight (JIS screwdriver helps). Spray lots of carburetor cleaner and use a toothbrush to clean it up and make sure it moves freely. I wouldn't replace it unless I verified an electrical issue.

Buckaroo

 

[Robb235]

Cleaned the idle air control valve this weekend. Of the 4 screws that hold the IACV to the throttle body, only 1 remained intact after I removed them. 2 I had to drill out and remove with an Easy Out. A third was so badly damaged by the time I removed it, I decided against reusing it.

I cleaned the IACV with some throttle body cleaner. There was a lot of crud and buildup in there. Makes me wonder why Toyota put it at the BOTTOM of the throttle body where all the crap drains to.

Hopefully this solves the issue.


Sent from my iPhone using Tapatalk

 

[Buckaroo]

Cleaned the idle air control valve this weekend. Of the 4 screws that hold the IACV to the throttle body, only 1 remained intact after I removed them. 2 I had to drill out and remove with an Easy Out. A third was so badly damaged by the time I removed it, I decided against reusing it.

Yes...they are very tight. I own several Vessel JIS screwdrivers - these really make a difference when removing pesky T4R screws like those on the IAC and the MAF and they also work great on regular Phillips fasteners....

https://www.vesseltools.com/handtools/screwdrivers/megadora/900-series-detail

More than you would ever want to know about JIS vs standard Phillips....

https://www.vesseltools.com/handtools/screwdrivers/whatsjis

Hope your problem is resolved.

Buckaroo

 

[Robb235]

I have a vacuum leak somewhere. My Long Term Fuel Trims are sky high at idle (35+), but even out when I am on the gas. All the hoses appear to be back in place, although some are starting to split at the ends due to age. Was I supposed to replace that gasket between the TB and IACV? I couldn't find that gasket at my local auto parts stores, so I reused the old one.

On the plus side, engine hasn't died since I've cleaned the IACV.


Sent from my iPhone using Tapatalk

 

[Buckaroo]

I have a vacuum leak somewhere. My Long Term Fuel Trims are sky high at idle (35+), but even out when I am on the gas. All the hoses appear to be back in place, although some are starting to split at the ends due to age. Was I supposed to replace that gasket between the TB and IACV? I couldn't find that gasket at my local auto parts stores, so I reused the old one.

Glad you got your stalling issue sorted out. I think I replaced my IAC gasket but as I recall, the old one looked like it could have been reused.

Check vacuum line routing using the underhood diagram. Make sure all the vacuum lines and the air induction tubing going from the air box to the throttle are well seated and that clamps are tight. If problem persists, check for vacuum leaks by spraying brake clean on vacuum lines, air induction tubing past the MAF & around TB, IAC and Manifold gaskets with engine running. If there is a leak, the engine will stumble. Use the small tube that comes with the brake clean to methodically spray each possible leak location and see if the engine responds - then go onto the next spot. Be careful as the brake clean is very flammable.

Buckaroo

 

[firemanj92]

So Sunday night I had done about 3 hours of interstate driving heading home. I get off the interstate and start heading up a mountain. I'm approaching a sharp turn in the road, and when I let off the gas, the motor died completely. Luckily no one was behind me, and I was able to restart and keep going. I approached another turn, let off the gas, and the engine died once more. I restarted, and then kept one foot on the gas, and braked with my left foot.

Only thing I can think of that would cause this, is that maybe the Idle Air Control Valve isn't opening quick enough when I snap the throttle shut, and it's causing the engine to die?

Thoughts?

Robert, Did you ever figure this out. I know you are doing an E85 experiment close to the same time. FWIW, I had the same issue with a lean code I found Toyo's in general don't like E85. Found out my better half accidentally put in E85. I went thru changing out everything from the fuel pump, regulator, filter, injectors, A/F sensor, O2 sensor, plenum gaskets,IAC and all vacuum lines with no luck, spoke to a few shop mechanics for insight. I then took care of the E85 with additives and it's been great ever since. -J

 

[Robb235]

Robert, Did you ever figure this out. I know you are doing an E85 experiment close to the same time. FWIW, I had the same issue with a lean code I found Toyo's in general don't like E85. Found out my better half accidentally put in E85. I went thru changing out everything from the fuel pump, regulator, filter, injectors, A/F sensor, O2 sensor, plenum gaskets,IAC and all vacuum lines with no luck, spoke to a few shop mechanics for insight. I then took care of the E85 with additives and it's been great ever since. -J

I don't think my experimentation with E85 is behind the vacuum leak. Previously my LTFTs were steady and predictably around +15 to +19 due to the higher ethanol content. When I cleaned my IAC valve and put everything back together, that's when my LTFTs jumped up to +35 at idle. The fact that they go back to +19 under load indicates a small vacuum leak to me.

EDIT: I haven't been able to hunt down the vacuum leak, been gone on a business trip.


Sent from my iPhone using Tapatalk

 

[Buckaroo]

I don't think my experimentation with E85 is behind the vacuum leak. Previously my LTFTs were steady and predictably around +15 to +19 due to the higher ethanol content.

Not to get off track but are you still running E85? You likely know this but the programming in the T4R ECU is not designed to handle that like a Flex-Fuel vehicle. Also - engines that are designed to run the higher level of alcohol have stainless components and different gaskets....have never tried it myself.

Buckaroo

 

[firemanj92]

I don't think my experimentation with E85 is behind the vacuum leak. Previously my LTFTs were steady and predictably around +15 to +19 due to the higher ethanol content. When I cleaned my IAC valve and put everything back together, that's when my LTFTs jumped up to +35 at idle. The fact that they go back to +19 under load indicates a small vacuum leak to me.

EDIT: I haven't been able to hunt down the vacuum leak, been gone on a business trip.


Sent from my iPhone using Tapatalk

I too thought the same thing, I had even replaced every vacuum line under the hood and still was running lean with high ltft's. As a side note ethanol itself does not burn like fossil fuels, it is a solvent. Most dual fuel vehicles lose mpg's when going E85 for this reason. Winter fuel blends already have increased ethanol here in CA and as you know adding corn to fuel doesn't benefit anyone but the corn industry which is another subject.

Hope you are able to solve the issue soon. -J