Jerry -- I'm having my 90k done next month at the dealer, and I'm going to ask them to replace this under the powertrain warranty, good will, or whatever. I've had the low idle shakes since 65k miles when the car was still under the powertrain warranty, so I'm going to press that it should be covered. I'll let everyone know what happens.

e

 

had my mounts replaced today along with my timing belt,idler,bearings,water pump.WOW my car idles at under 500 rpm with no more shake,motor mounts were toast.car feels new again at 154000 miles you wouldn't no it.

 

These are the exact things I'm replacing next month (hopefully my dealership will step up and cover the mounts under the powertrain warranty or good will). Glad to hear no more shakes.

 

So I was in a quiet neighborhood the other day at a stop sign.. With my two front windows down half way..I could not hear or feel the engine at all. Those who dont know would probably think I didn't start my engine yet. heh.

 

Just bumping an old thread that I started. Hope all the old-timers are still out there.

When I started this thread 3+ years ago, I was having a low idle issue with the climate control on. If the outside temp was above 32 degrees, with the climate control on, in drive, stopped at a light, the RPMs would always be around 650. However, if the temp dropped below 32 degrees, even with the climate control on, the RPMs dropped to 400 or less, and the car would begin to shake. I assumed this was normal, and I just learned to deal with it.

Just recently, however, my a/c went out. The dealer said it was low on freon, so they recharged it. Now, the a/c works great, but there's something that's turning on and off while I'm sitting at a stop light that's causing low idle, even with the a/c on and blowing cold. I'm trying to figure out what it could be.

So here's the question. What parts of the climate control system turn on and off that would cause the RPMs to fluctuate. And the second question would be what about recharging the freon could cause the system to behave differently than it has for the past 5 years. I assume the compressor turns on and off, but I don't think that's the problem, because like I said above, I never had the problem before as long as the temperature was above 32 degrees. So, for example, at 40 degrees, with the climate control on, I never had low idle, and I assume that the compressor wasn't on all the time at that temperature.

Anyone?

 

Hey e,
I remember this issue has been floating around forever...I think what is going on is that when the compressor is off and its clutch is disconnected, the load on the engine and the drive belt changes, and just happens to cause resonant vibrations. When the compressor engages the vibrations change and are not resonant anymore. I don't think there is much we can do about it without changing a bunch of engine characteristics and parts. Drives me nuts too.

PS: This makes sense in the context of the motor mount replacements fixing the problem. The new mounts change the resonance of the engine 'system'.

Jerry

 

Hey Jerry. Glad to see you're still hanging around.

I think I understand the problem, but my question is a little more specific. I've always had the low idle problem, but I was able to make it go away by leaving the climate control on (which I always do anyway), and provided the temperature was above 32 degrees, there was no low idle. However now, after the freon recharge, even with the temperature above 32 degrees, I sometimes get low idle because something in the climate control system is turning itself on and off now that didn't used to turn on and off before. I'm just trying to figure out what that could be and why a freon recharge would change the dynamics of the system so that I have the problem now, even with the climate control system on and with the temperature above 32 degrees. Does that make sense?

 

Ahhh I see, that's a good question. I think I've seen this kind of thing happen before, after refilling my refrigerant. I'll guess what happens is that the system becomes more efficient at cooling, and that there is some thermal feedback in the system somewhere that causes the cycling, so that the compressor doesn't need to run as much. Could even be that the compressor gets hotter from the excess refrigerant pressure and cycles itself? I'm not really sure what kind of thermal feedback is involved with the compressor, where the sensor(s) are, etc. If I remember correctly, what happened with my 4Runner is that the cycling will even out and go away again after a short period of time (maybe a week or so?). I'd wait it out for a while and see if the problem goes away again. Now that you've mentioned it, I haven't noticed any quick cycling with my 4Runner since I charged it, the problem went away and I never even realized it.

 

Okay, now I think we're getting somewhere. I was thinking the same thing. Is it possible that they overcharged the system? I would think that with the pressure too high, the compressor would turn on and off more frequently than it did before. Also, I have to wonder how the freon got low in the first place? When they recharged the freon, they added dye to see if they could detect a leak, and after a few weeks when they re-checked it, they found no leak at all. One thing I forgot to mention is that my original compressor konked out on me last summer, so I did have the compressor replaced. It's possible that the guys who installed the new/used compressor didn't recharge the system with enough freon, and that it was only a matter of time before it got to the point where the system wouldn't cool anymore. But, then again, that implies a leak somewhere, and Lexus couldn't find one.

It's been about a month since the freon recharge. I'll give it some more time, but assuming there's no leak, then the pressure will remain at it's current level and the compressor will continue cycling on and off. Is it ever advisable to release some of the freon to bring the pressure down to a lower level? Just a thought. Thanks again for your help.

Eric

 

eric a few things man....one FIRST AND FORMOST, do u have the high and low pressures on the system? if not this is 100% the first thing you should do. second if u wanna save some $ get away from the dealer for this...i promise u, u can find a trustworthy/dependable toyota/lexus mechanic for half of what they charge for HVAC stuff.

if they over/under charged your system, your car could easily be hitting the high/low pressure sensors causing the compressor to turn on/off although it SHOULDNT stall the car

who put the replacement compressor in? did they replace the drier when they did this? more than likely not....most people dont ALTHOUGH this is the correct way to replace a compressor.

again....the pressures on the high/low are the keys in helping diagnose those. if u dont have these, go NO farther till u get these.

also a easy helpful tip that probably wont help BUT DEF WONT HURT and i recommend it to everyone YEARLY. go to a HVAC supply house and get a chemical (if they carry it) called Nu-Brite Condenser coil cleaner and degreaser made by a company called Nu-Calgon.

here is a link to it....even cheaper than we sell it to a cash ticket (bout the same price our good customers pay for it)

http://www.patriot-supply.com/produc...item.cfm/47476

its a foaming coil cleaner, spray the radiator with water (with hood open engine cooled) then spray this on it (its a aerosol can) and let is soak, it will foam and push out any dirt trapped in the fins out, then make sure u wash it off thoroughly.

 

Thanks Sak. No, I don't have the high and low pressures. I will try and get those and post them up.

Also, the car doesn't stall. It just gets the low idle that it never had before with the a/c on. I assume the pressure is on the high side now, which is causing the compressor to cycle off, but I won't know for sure until I get those levels read.

As for the place that installed the new compressor last summer, that's all they did is replace the compressor. They may have recharged the system as well (I assume you have to do that when you take off the compressor, right?), but I really don't know. They definitely didn't replace the drier. Is that an expensive part and/or difficult to replace? Does the drier draw enough power from the car to cause the RPMs to go up? Does the drier cycle on and off like the compressor? I do notice that I never have the low idle problem when it's raining outside. Does the function of the drier have something to do with outside humidity? My sense is that it does.

Anyway, thanks again for your help. I think I'm getting closer to figuring this out. Lexus took a look at it last week and couldn't find anything wrong, but because I've had the car for so long, I definitely know that it's not behaving the way it used to.

I'll also look into getting the cleaning agent you mentioned. Thanks for the tip.

e

 

yea, if they replaced the compressor, they def recharged the system. they shoulda have replaced the drier but due to costs they might not have. as stated it is the proper way to due it but 80% of shops will cut this corner. if your compressor "burns" out though it should be mandatory to change both and i would even advise a system flush. no, the drier uses no voltage it is a pre-cautionary devise to keep particles out of the compressor/condensor. think of it as a filter.....

no, the drier isnt affected by humidity, no more than a regular ac system. only electrical parts on a car's SEALED cooling system are the clutch on the compressor and if the car has electronic expansion valves (not all cars use electronic ones).


Your welcome man...my advise unless u REALLY wanna spend some $ is still to take it away from the dealer as they arent gonna be a specialist on this anyways more like a parts re-placer which will end up leaving u broke

 

do our cars have a separate drier part? can't find it anywhere.
When the drier fails, moisture enters the system, and:
sounds quite like the described symptoms to me.