Hi....I've searched the threads and haven't found any problem directly related to mine. I have a 95 SC400 with 51,000 miles. I have given it a complete tune-up recently so that should not be a contributing factor.
When I turn the a/c on, the idle jumps up to about 1100rpm and stays there for about 5 minutes of driving and then returns to normal. However, if I turn the a/c off while idling, the car will start to misfire and stall. The only diagnostic code stored is 31 which I believe points to the airflow sensor, however, it is strange that this only occurs in conjunction with the a/c.

Any suggestions would be great.

Thanks,
Kevin

95 SC400

 

Hey Kevin,

It seems that both of our cars have the same **** wrong with them, I have a 95 SC4 with 70K on it and it does the exact same thing. I have 2 ideas on how to fix it: one is first turn off the ac light then the actual blower and it doesn’t "seem" to stall anymore, and I noticed that there either might be a problem in the vacume system for the AC or that the sensor that controls the engines Rpm's is malfunctioning. Anyway if u find an answer keep me posted and ill do the same if I here anything.
Thanks,
Tommy

 

Seriously, this IS just a wild axx guess...

Suppose the engine intake filter you just changed out was COMPLETELY clogged up, the engine ECU had adjusted, over time, to this and now suddenly it's "confused" with too much airflow.

I haven't really been buying into the issue of disconnecting the battery for 30 minutes so the ECU memory gets completely wiped but in this case it might be worth a try.

 

I've already tried the resetting your computer, I've let it seat for overnight. It doesn't work and my AC still acts the same as above... But, hey it still works... Just don't turn your AC off while stuck in traffic. This happened to me once, I was stuck in the freeway going about 45MPH and I decided to turn the AC off, I guess I was getting cold, well I my car stalls and I had hard time manuevering it, good thing I didn't get into an accident. BTW, I also have '95 SC400 with about 100,000 miles on it. It got me curious, is there any other '95 SC400 with similar problem in this forum?

 

I also have tried the computer resetting with no success. I found my TPS to be slightly out of adjustment so I fixed that and the stalling got better for just a little while and is now back to the way it was before. I also took the car to a Lexus dealer to have them check it out, however they claimed that it would take around 8 hours for them to diagnose. Personally, I am pretty sure that they just didn't have time that day to work on it and needed an excuse (BTW, they also blamed my aftermarket remote start as a possible cause.) At least they washed it for me!

 

If you have to turn the A/C off for some strage reason while idling, can't you pop it into neutral, and rev a little then turn the a/c off?

 

I've tried popping it into neutral and revving. However, as soon as you go back into drive, it wants to stall again. It's not unliveable, just annoying. As for turning off the a/c, when the outside temperature is relatively cool and the a/c doesn't need to work very hard, the car will automatically cycle the compressor and when it cycles off, the problem becomes apparent. On warm days, it doesn't matter because it stays on constant. Thanks for the responses.

 

my 95 SC400 does the same thing. SOunds like this should be taken up with toyota for a possible recall.

 

I'd always keep the A/C on then.If your too cold just crank open the windows and adjust the vents so they face down and not blowing in your face. :eek:

 

I have a 95 sc400 and THIS EXACT problem. I've taken it into many mechanics and Lexus at least 3 times (and spent the money to diagnose). Each time, they end up either:

a) Giving me a minor tune up
b) Cleaning out my fuel injectors
c) Recommending some ludicrous repair

(a) and (b) fix the problem for a bit. But I'm beginning to believe this has more to do with them resetting my computer each time I take it in.

It's (somewhat) comforting to know that others are experience the same problem with their cars. Hopefully somebody has gotten the dealer to really pinpoint the problem.

One thing that was mentioned during one of the services was the "Idle Air Control Valve"??? I'm not a mechanic, so I'm not quite sure what this is (or does). My buddy's SC400 stalled a few times with this A/C issue - so I'm beginning to believe that this is a problem with the car that Lexus should definitely be addressing.

 

Lots of idle problems on older fuel injected cars come as a result of gunked up throttle bodies. Has anybody tried cleaning their throttle body? There are usually small passageways (or even a tiny gap around the edge of the throttle plate) in the TB which allow for air to bypass the throttle plates for base idle. When more air is needed to compensate for a load such as the P/S, A/C or alternator, the computer has a little valve that it can fiddle with to add more bypass air.

 

There are two items that directly control idle speed;

Idle Speed Control Valve (on front of motor).
Idle-Up Controller (on bulkhead).

Either of these have to be considered suspect, or possibly the vacum hoses that are attached.

 

My Idle Speed Control Valve was replaced about year ago or so. And lately, within a month, my car stalled twice when I turn the AC off while driving slowly.
I also noticed that while at idle if I turn the AC off, the idle jumps down to about 200 RMPS and then picks up to about 500 RPMS.
If I have to guess, it's ether dirty throttle body or actual ECU programming glitch. Unfortunately, when I cleaned the throttle body about 20K miles ago, I also did the AC test when at stand sill with the same result (the idle would go down to 200RPMS about go back up to 500RPMS).

 

sounds like it could be an air leak on the inlet manifold/throttle body or a leak on one of the vacum hoses/power brake booster.

 

Since reading this post few weeks back, I started to pay more attention to A/C. So far, within a week or so, I was able to stall my 95 SC400 three times. Mine doesn't misfire, it just drops to 0 RMPS and dies. Also I don't have a problem where it stays at 1100 RPMS for 5 mins when I turn it on. Mine goes up to 1000 RPMS and drops to 800 RPMS within seconds.
Anybody know exactly what could be causing this?