Hermosa

I think London Bill might be on the money here. If you lose vacuum your car would have really rough idle and would stall at lower rpms. The AC on just raises the RPMs enough to keep the car going and create enough vacuum.

Check your entire intake assembly and look for degraded seals or tubing. You may have to remove the intake but that is simple.

Please list your starting RPMs and then the RPMs when your SC starts to have issues.

ChrisK

iTrader: (1)

I checked my tubing and everything looks normal. Also, car runs smoothly, it idles smoothly, it accelerates smoothly. The only problem I have is when turning the AC off. My car idles at 500 RPMS when in gear (the AC off), with the AC on it sits at 800 RPMS after initial jump to 1000 RPMS. If I would have vacuum problem, it would have to do with the AC. What vacuum lines control the AC? Personally, it I have to point fingers at the problem area, it would be the ECU programming that by my standard is not 100%.

Thanks for all your help,

kklotz

I agree with Chris. If I start the car and turn the A/C off within the first minute or so, everything is fine. It runs perfectly smooth. If I then turn on the A/C, I get an initial jump to about 1000 rpm and then a decrease to about a steady 750-800 rpm. The car still runs smooth. However, if I turn off the A/C after having it on for at least a few minutes, the rpm drops to about 400-500 and it may start to stumble and/or stall. The same thing happens if the car is started with the A/C on and then it is turned off after driving for a while.

I know these cars have some ground connection issues that cause funny things to happen. For example, a bad negative battery cable that I have heard causing starnge things. Would something like that or a bad ground to the ECU be possible?

-Kevin

London Bill

ChrisK/kklotz

My understanding of the Idle Speed Control Valve & Idle-Up Controller is that it will compensate for the additional load imposed on the engine at tickover when using A/C, power steering, head lights, etc, this is electronically controlled almost certainly by the main ECU or is at least linked to it's operation.

If you have any air leaks on the inlet or power brake system this will cause a loss of vacum and make the revs drop, the idle control will try to compensate for this (if it is working correctly). Air leaks in the power brake system normally cause a big drop in revs (causing a stall in lessor cars), when the foot brake is applied.

I dont see it as an ECU issue, a failure in that department would be more drastic and would normally result in OBD warnings, a fault in the idle control/idle-up system or air leak on the inlet is more probable, that does not say you can rule out ECU issues it is just less likley.

ChrisK

iTrader: (1)

London Bill,

Wouldn't air leak also cause problems when A/C is off? Wouldn't the car run bad even with A/C off/on? My car only stalls when running A/C for a while and while idling I turn it off. Otherwise everything runs properly. Why I say that there is the ECU programming glitch because everything runs OK except when playing with the AC. Try this for me, when car is hot and at idle while in Drive turn on the AC. Did RPMS jump up, and after the split second go little bit down? Now, after running with the AC on for a while, at idle while in Drive turn the AC off. Did RPMS go down and then slightly up? If you can recreate behavior like this you will see why I believe that ECU is not fast enough to adjust the car when AC is on or off. I can imagine that a lot of SC owners can recreate this behavior. Difference between kklotz's and my car is that RPMS drop low enough for the car to stall.

Also, when the car is cold, did you ever notice RPMS staying at higher level even when the car gets hot? My RPMS jump down to norma idle speed only if my car idles for about 5 seconds at stand still. If I don't let the car sit still for more than 5 seconds, I can drive all day long stopping and going and RPMS will never drop lower than when car was cold. And that I also believe to be a problem with the ECU taking it's sweet time to adjust everything properly.

London Bill

ChrisK;

If it is not an air leak it may well be the idle control system playing up (as stated above).

Resetting the ECU can bring the hot RPM back in to the zone, although mine will climb back up to a fast idle (800/850rpm) over a few days.

London Bill

You might find this helpful

http://www.autoshop101.com/forms/h26.pdf

ChrisK

iTrader: (1)

London Bill,

I briefly read through this article. Both the Idle Positioning Sensor and Idle Control Valve were replaced on my car about 1.5 years ago, and they are not the items that break or wear out with time. Also, as you can see the Idle Control Valve is controlled by ECU, so with the wrong ECU lookup tables the car won't run properly. I personally believe that Toyota/Lexus did not do the best job programming the ECU. The scenarios I posted previously I believe to be the proof of it.

Coming back to the problem. I did reset the ECU before taking my car for 90K service. The timing belt, water pump, idlers and tensioners were replaced at that time. Also, the serpentine belt tensioner was making noises so I got that replaces as well. Of course, I asked the service guy to take the look at the stalling problem while at it. When I picked up the car, he told me that they could not recreate the problem. When driving back home I tried to get the car to stall, but I could not to do so. On the other hand, as I said before, while turning off the A/C the RPMS drop to about 200 and then go up to 500. Because of it, I still believe that the problem is related to poor ECU programming rather than anything else.

Thank you for all your time and help.

supraturbo OLD

Hello all,

After reading all your posts, I have the same problem, but my problem is on '94 ES 300. I took it to the dealer, and they said that Idle Air controller (IAC) is sticking. I will check with the dealer to see what exactly do they recommand.


Does anyone know how much does the IAC cost?

Thanks

'94 ES 300 108K miles.
3 new O2 Sensor
1 Cat. Converter.

lexian

I believe I have found a solution to your all engine stalled. Three solutions to this symtom, but it depends on your situation when your engine is warmed up or cold.

-If your engine is cold at start up in the morning and the engine shuts right off, then it is the Cold Starter Valve or the Air Intake Valve needs to be cleaned. The Air Intake Valve is easy to clean with Gumout spray. The Cold Starter Valve was cleaned by the dealer and that was what they said it was the problem after they fixed it, and it sounds reasonable to me.

-If your engine is at a normal temparature and it stalls when idling, at red lights, etc, turning your A/C on will increase the idle speeding helping it not to stall. Cleaning the Air Intake Valve does help, even if it does not resolve your problem, it help to smooth up your gas pedal and the valve itself so you will not waste your time there. But I have found the actual cause on this symtom when my brothers car 2001 ES300 stalled at a normal temperature. This is a big job to resolve!! It is the engine speed sensor that causes this problem. Once the sensor is dirty, for some reason it will send a signal to the ECU or something to shut down the engine. Over time the sensor is cover with a layer of oil burned like, that is very hard to remove; like a cooking pan fried oil. if you have a better way to clean it please keep us posted. We had to sand it down nicely with fine sand paper. This problem occurs on any car that has this sensor not only lexus. The sensor is located right at the engine pulley, the job to clean this sensor is the same as replacing timing belt. You have to remove the timing belt cover to access to it. After we cleaned it, the engine starts right up with no trouble. This problem will recur when this sensor is dirty again. Cleaning the Air Intake Valve is a good idea every 15k when the car has 30k on it. If you pay attention on your gas pedal, you will feel the stickiness of the pedal movement, it is time to clean the Air intake valve.

Good luck to All

lexian

Hello All,

I believe I have found a solution to your all engine stalled, at least it worked for me. Three solutions to this symtom, but it depends on your situation when your engine is warmed up or cold.

-If your engine is cold at start up in the morning and the engine shuts right off, then it is the Cold Starter Valve or the Air Intake Valve needs to be cleaned. The Air Intake Valve is easy to clean with Gumout spray. The Cold Starter Valve was cleaned by the dealer and that was what they said it was the problem after they fixed it, and it sounds reasonable to me.

-If your engine is at a normal temparature and it stalls when idling, at red lights, etc, turning your A/C on will increase the idle speed helping it not to stall. Cleaning the Air Intake Valve does help, even if it does not resolve your problem, it helps to smooth up your gas pedal and the valve itself so you will not waste your time there. But I have found the actual cause on this symtom when my brothers car 2001 ES300, ( I am RX myself and this problem will occurs on any vehicle with this sensor) stalled at a normal temperature. This is a big job to resolve!! It is the engine speed sensor that causes this problem. Once the sensor is dirty, for some reason it will send a signal to the ECU or something to shut down the engine. Over time the sensor is cover with a layer of oil burned like, that is very hard to remove; like a cooking pan fried oil. if you have a better way to clean it please keep us posted. We had to sand it down nicely with fine sand paper. the sensor looks like an aliminum Capacitor. This problem occurs on any car that has this sensor not only lexus. The sensor is located right at the engine pulley, the job to clean this sensor is the same as replacing timing belt. You have to remove the timing belt cover to access to it. After we cleaned it, the engine starts right up with no trouble. This problem will recur when this sensor is dirty again. Cleaning the Air Intake Valve is a good idea every 15k when the car has 30k on it. If you pay attention on your gas pedal, you will feel the stickiness of the pedal movement, it is time to clean the Air intake valve.

Good luck to All

quikturbo

Well,
there is one other thing that can cause these symptoms. Believe it or not, its a leak in your fuel system. What I mean by this is a leaky injector o-ring, or faulty fuel pressure regulator. This was the case on my daily driver.

I had to have the compressor (AC or Heat) on at all times or the car would idle, stall, etc.. Finally, the leak got so bad it wouldn't even stay running. I still am unclear as to its direct correlation to having the ac on when there is a leak in your fuel system . I will say, I didn't smell any fuel. My fuel pressure was simply all over the place. I changed out the injector o-rings, and fpr and the car idles and runs like a dream, even with the ac off

I'd recommend checking the static fuel pressure of the car, and see if its jumping up and down. If it is, that could very well be your problem.

Regards,
Chris

nextlevelcoupe

iTrader: (1)

this problem is caused by a failing electonic Idle Control valve located at the front top of the engine. looks like a little black module near the throttle. already priced this part-dealer wants $600 for this little,(what looks like)$20 part.-

i thought i was the only person with this problem,but for that kind of money,i will live with it-unless one comes along @ a good price

cheungsta

I know this is kind of an older thread, but I just got my 95 SC400, and I've been experiencing the same stalling problem! It really freaked me out, but I feel a lot better knowing that it isn't my specific car, but a pretty common problem with 95 SC4s.

Did anyone every figure out a true solution to this problem? Or am I fated just to keep my AC on all the time?

cheungsta

Soo....has anyone actually gotten this Eletronic Idle Control Valve replaced? If it is replaced, will it cure the "stalling-when-AC-is-turned-off" problem?

For those of you who have 95 SC400s, what have you guys been doing about the little condition? Did you just get accustom to the conditions? I'm just wondering what's the best way to approach it...whether or not I should try and fix it car-wise, or if I should adjust the way I handle my AC when I drive...