Savon's Lexus

Gs Looses Power While Ac Running

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Hi all ,

I have been experiencing the wierdest thing, i have had the altnernator checked, several new batteries but when the AC is running and i have to sit idle for any long period of time , i notice my car loose power, the radio starts then the check engine light comes on and if i turne the AC off the power restores to its normal level and all is well. This issue is really bothering me because i never knwo when its going to do it, i don thave to sit idle long at all but i have noticed it always happen when the AC is on and well heck its too dang on hot not to use the AC. ANyone else had this issue or ar there post already out there you can refer me too?

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There's a powerdrain of some sort. I assume your car is serviced at specified intervals (this rules out sparks, filters and etc.)

To check for:

- Did you read output from charging system under full load (lights, blower, wipers, radio, AC, heated windows ON)? Output should be around 14V, you may have to revv the engine a little.

- negative cable from battery (corroded)

- AC compressor / clutch going bad (does your RPM@Idle drop notably when switching AC on?)

- worn or slipping S-belt, bad tension.

- catalytic convertor or air/fuel chain can be clogged (should trigger engine warning light)

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sorry for the long post, but i believe information=knowledge=power :)

this is interesting... my friends car was/is having similar problems, here's the situation:

we live in New Mexico so it gets pretty warm in the summer, and now that summer has hit us, this problem has popped up. it all started when the ignition interlock failed (bad choices, my fault, i failed as a friend, anyways...) that seemed to short something out and the battery got completely drained. a jumpstart the first day worked fine, but the next day at work, a jump didn't do anything and the interlock was having problems. so, we towed it to get the interlock reinstalled/serviced... done. the next day, she was at a stop light with the ac running, and the car felt like it was about to die (power drain?). the radio's volume would fade in and out and the car was on the verge of stalling. the car was taken to autozone and had the alternator checked. both the alternator and drive belt were found to be bad(i guess the alternator was tested "in car"), so both were replaced on the spot. however, after they were replaced the problem continued. that is to say that, while idle, with the ac on, the car seemed to be on the verge of dieing. this perplexed the autozone guys, so they tested the alternator a second time "out of car"... this time the alternator came back fine. my friend doesn't take any crap from anyone, she's an amazing girl! so she spoke to the manager, and because of the situation, got a new battery, the original alternator put back in, and was only out the cost of the belt. the next day, same thing... stopped at a light, ac on, radio in and out, seemed to be on the verge of stalling. so she had a different mechanic look at it while at work and he concluded that the alternator was bad (again). so i decided to just replace the damn thing myself... done. now, i can understand that even though the battery was replaced, if the alternator is bad it's not going to recharge the battery. this was the case for a couple days before i actually replaced the alternator. so once i got the new alternator installed we fired up the car and everything seemed fine. we turned on the ac full blast and i felt first hand what was going on... the car was idle (just under 1000rpms) but once the ac was turned on it would drop down to 300/400rpms? up, down, up, down, up, down ect... i thought that if the previous alternator was bad then the battery may have been drained even though it was new (as the car had been driving two days before i put in the new alternator) so i sat there for a few minutes idling the car a little bit higher to recharge the battery... within a few minutes this seemed to fix everything! radio on, full blast, no problem, ac on, full blast, no problem. two days! no problem! but now, the check engine light has come on!? so this is the point where im not sure what to do...

so i can verify that;

1. the negative cable to battery is in clean condition

2. the s-belt has been replace and is within measure (this is the one belt in front right?)

3. new alternator

4. new battery

but how can i trouble shoot;

5. AC compressor / clutch

6. catalytic convertor or air/fuel chain clogged

im also looking into seeing how much it would be to have a tech/mechanic read the error codes that should be generated from the check engine light.

i know i need to top off the oil, she is running a little low, and will be doing a full oil change for her come july. i know i can do that. im also gunna find out how to check spark plugs (never had to do that, so i'll be researching that now) so lets assume those will be fine... i'll repost if thats not the case and fixes the problem.

THANKS IN ADVANCE!!!

These board have already been such a wealth of information!!! everyone here is super badass in my book!

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Before you go into extensive checking, you need to read the ECU codes first. Read this link for some help on OBD2 ECU codes: OBD nfo A respectable bodyshop can read it out for free or a small fee.

There might be a link between switching on the AC, severe dropping of RPM's and/or a compressor/clutch going out. Let a mechanic listen to the compressor's debris (with a stethoscope) and measure the AC's high/low pressure. Compressor problems can be intermittent, you really need to rule it out.

Backpressure test can be done for a clogged exhaust chain etc, but I would take it one step a time.

Make sure your oil level is between the low/high markings, if not, refill a drop.

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well, the car started acting really bad at the light the other day, so my friend immediately pulled off the road into a parking lot and it died right there at the entrance and it would not start again... so we got a tow back to the apartment and i bought a little obd2 code reader on sale. so its only giving one error P0505 which from the list you linked is an "Idle Control System Malfunction" so i searched the forum and come across a similar post referring to an "air control valve?" the post was for an RX, but i assumed the GS would have similar hardware. i downloaded the service manuals but am having a hard time figuring out where this valve is, so that i might be able to check it...

i'm still doing my best to do my research, but i thought i might benefit from posting an update.

:::new update:::

i just went over and tried to start the car again... it's sounds SOOO close to starting. then i poped the hood, and there was this weird... buzzing? sound coming for the "throttle body" area. i don't have a stethoscope or anything like that so i shoved the square end of a ratchet wrench to my ear and started poking different parts of the engine with the other end... the sound definitely gets stronger in the "throttle body" area. is it difficult to remove the throttle body to clean it? what about the IACV (intake air control valve?) where the heck is it?

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2GS have electronic throttle control, they do not have IAC valves. The electronic throttle motor modulates constantly to regulate idle speed. Re. cleaning the TB, it's not that complicated and you can find some DIY's/info via the search option. Also check your TPS.

Here's a diagram:

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awesome! Thank You! that confirms what i finally found in the big manual, and understand now that the buzzing sound is supposed to be there. i had a little volt/ohm reader and tested the MAF, the Throttle Motor, Throttle Sensor, and Accelerator Sensor like it said to in the manual and everything came back withing the measurements it said, so it looks like none of those are bad... i just don't know where to go from here. this has obviously left the scope of the original A/C problems... now the car just wont start... im thinking fuel path? any pointers on where i can get more info on troubleshooting that? fuel pump, fuel filter, ect...

:::update:::

finally found the info i was looking for, but at this point it doesn't matter, she was able to sell the car for a good price, i just want to thank you intaker! your info helped me so much, and these board have provided me with alot too... i really learned alot. Thanks everyone!

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sorry for the long post, but i believe information=knowledge=power :)

this is interesting... my friends car was/is having similar problems, here's the situation:

we live in New Mexico so it gets pretty warm in the summer, and now that summer has hit us, this problem has popped up. it all started when the ignition interlock failed (bad choices, my fault, i failed as a friend, anyways...) that seemed to short something out and the battery got completely drained. a jumpstart the first day worked fine, but the next day at work, a jump didn't do anything and the interlock was having problems. so, we towed it to get the interlock reinstalled/serviced... done. the next day, she was at a stop light with the ac running, and the car felt like it was about to die (power drain?). the radio's volume would fade in and out and the car was on the verge of stalling. the car was taken to autozone and had the alternator checked. both the alternator and drive belt were found to be bad(i guess the alternator was tested "in car"), so both were replaced on the spot. however, after they were replaced the problem continued. that is to say that, while idle, with the ac on, the car seemed to be on the verge of dieing. this perplexed the autozone guys, so they tested the alternator a second time "out of car"... this time the alternator came back fine. my friend doesn't take any crap from anyone, she's an amazing girl! so she spoke to the manager, and because of the situation, got a new battery, the original alternator put back in, and was only out the cost of the belt. the next day, same thing... stopped at a light, ac on, radio in and out, seemed to be on the verge of stalling. so she had a different mechanic look at it while at work and he concluded that the alternator was bad (again). so i decided to just replace the damn thing myself... done. now, i can understand that even though the battery was replaced, if the alternator is bad it's not going to recharge the battery. this was the case for a couple days before i actually replaced the alternator. so once i got the new alternator installed we fired up the car and everything seemed fine. we turned on the ac full blast and i felt first hand what was going on... the car was idle (just under 1000rpms) but once the ac was turned on it would drop down to 300/400rpms? up, down, up, down, up, down ect... i thought that if the previous alternator was bad then the battery may have been drained even though it was new (as the car had been driving two days before i put in the new alternator) so i sat there for a few minutes idling the car a little bit higher to recharge the battery... within a few minutes this seemed to fix everything! radio on, full blast, no problem, ac on, full blast, no problem. two days! no problem! but now, the check engine light has come on!? so this is the point where im not sure what to do...

so i can verify that;

1. the negative cable to battery is in clean condition

2. the s-belt has been replace and is within measure (this is the one belt in front right?)

3. new alternator

4. new battery

but how can i trouble shoot;

5. AC compressor / clutch

6. catalytic convertor or air/fuel chain clogged

im also looking into seeing how much it would be to have a tech/mechanic read the error codes that should be generated from the check engine light.

i know i need to top off the oil, she is running a little low, and will be doing a full oil change for her come july. i know i can do that. im also gunna find out how to check spark plugs (never had to do that, so i'll be researching that now) so lets assume those will be fine... i'll repost if thats not the case and fixes the problem.

THANKS IN ADVANCE!!!

These board have already been such a wealth of information!!! everyone here is super badass in my book!

OMG , this is exactly what mine is doing , i have gotten new belts, new batteries, the alternator was tested several time and charging correctly, new catalytic converter has been put on , it's been turned up , new gaskets put on , this is my only issue lol and its causing me great grief. I need to find this needle in this haystack.

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When the A/C compressor is turned on, it adds extra load to the engine. The electronic throttle receives a signal that the load at idle has increased. The ECM adds a little throttle to the engine to compensate for the load. This increases engine speed slightly when the A/C cycles on. When the A/C cycles off, the throttle is decreased slightly to return the engine to no-load idle speed (A/C off). When the A/C is on and is running normally......and this is the same for any vehicle with A/C......the A/C compressor cycles on and off to maintain the set temperature inside the car. If you let any vehicle idle with A/C on you will hear the A/C clutch engage (clicking sound), immediately followed by an increase in idle speed, and another quieter click, immediately followed by a slight decrease in idle speed. This process repeats with the A/C on. If the engine speed don't increase when needed to run the compressor, and the engine stays at its no-load idle speed, it will slow down under the strain, run rough, near stalling (maybe even stall) and the alternator will not be turning fast enough to excite and produce a charging current. This is why the battery dies in a hurry. The cause of this problem is simple on paper, but it may be tricky to find the exact cause of the problem. (ECM, A/C amplifier, poor electrical connection, Throttle control valve or IAC valve for vehicles not equipped with "Drive-by-wire"). Have a scan performed by your Lexus dealer. It will be much faster and probably cheaper in the long run, rather than replacing alternators, batteries and chasing "Might Be's". Good Luck! P.S. When an alternator runs at a stalled/excited stage, caused by slow speed and high load, it will burn out and/or suffer damage.

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2GS have electronic throttle control, they do not have IAC valves. The electronic throttle motor modulates constantly to regulate idle speed. Re. cleaning the TB, it's not that complicated and you can find some DIY's/info via the search option. Also check your TPS.

Here's a diagram:

I had the same problem and this was the solution.

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Currently having this same problem with my Lexus GS400. Every time i turn my a/c on somehow my car starts losing power, first the RPM gauge goes up&down for a little while then after a while radio starts fading in/out, a battery light comes on when in park. I done had my alternator replaced twice within the past 3 4 months. When i have everything off car runs fine but when i start turning things on it die down especially when a/c running.

PS:Just checked my alternator again the other day it was reading 13.9v but when i turn the a/c on it dropped to12v-12.7v...

I NEED SOME HELP PLEASE THIS PROBLEM REALLY URKING ME AND ITS TOO HOT OUTSIDE FOR THIS ESPECIALLY TO NOT DRIVE WITH A/C

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