avalon42

iTrader: (1)

I've noticed that with the compressor engaged, it dips in engine rpms. I've compared it to my friend's LS, his RPMs actually go up. AC is ice cold, no problems whatsoever when driving on the freeway. But at a stop light, I can tell my car is struggling to stay on.

I was wondering if it had to do with the idle control valve. The reason why its nagging me is because my car is under load, and the overall system voltage dips to less than 12V (sometimes goes down to 10.8V). This can't be good for the battery in the long run.

What RPMs does your LS hover at with the AC engaged?

JimsGX

Mine goes up as well. Around 750~775rpm with the AC on.

python

iTrader: (4)

tps is what controls that function, check it with an ohm meter,and feeler gauges, do a search and u can find out how to do it...im surprised ur ac works at all with the voltage drop, the clutch requires a certain amount of voltage otherwise it will not work,much like a starter solenoid will rattle if it gets low voltage

avalon42

iTrader: (1)

It turns out it was the idle control valve, I spent nearly an hour taking all the connections off just so I could take a look inside. It was FILTHY! I did remember that we did clean my intake plenum really well when we removed the starter, yet we should have taken a gander at this sucker while we had it out. It was a PITA to remove and replace. I cleaned it using Autozone Brand Carb Cleaner, a few liberal passes and viola! most of the crap is gone and I can see straight to metal now. ***UPDATE DO NOT USE THIS **** ON YOUR IACV*** read more info below...

I also gave my AFM(MAF) whatever you call it a good cleaning as well, using CFC brand MAF Cleaner. I gave it two runs of liberal spraying, then let it dry for an hour or so while I tinkered with the idle control valve.

The LS purrs like a kitten but unleashes like a cheetah now. Wunderbar.

LiCelsior

iTrader: (32)

lol...hahaha i like ur post avalon.

same as me, i cleaned my plenum well when i replaced my starter also, also used a wire brush as there was a good 2-3mm of grime on there. yea the iacv is a pita to remove though, especially those damn coolant hose.

avalon42

iTrader: (1)

Yea, the big fat one that connects to the back of the thermostat housing area...it held the IACV from me prying it off. Drove me nuts for about 10 minutes. After the ten minutes and two cigarettes later, I figured out how to yank that sucker off. For the love of Christ people, do this while you have you're doing a major tune up with the spark plug wires removed or something. It will be WAY easier because you're taking off vacuum lines and crap to make way.

python

iTrader: (4)

normally when the iac valve goes it will surge...glad to see u fixed it

omarg

dont you love how LS problems are so easily fixed? almost everything that starts to malfunction on my car can be brought back to life if you just tinker/clean it.

can somebody direct me to where the iacv is? i would like to clean it on my/family's 4 ls400s.

I'm infatuated with toyota build quality.

avalon42

iTrader: (1)

I attached a pic to this post, so it'll make it easier for others to find it.

Keep in mind, it's quality parts, but questionable placement and accessibility. There are 3 coolant hoses running through this, as well as an electronic connector. If your plastic is as brittle as mine, you might want to have some black silicone on standby to hold in place. My clip disintegrated completely. The paper gasket that was behind it. Disintegrated. You will have to buy some FIPG to replace it, as no other parts place besides the dealer carries it.

You might be able to get away with spraying some carb cleaner into that giant fat hose on the side of the IACV.

omarg

thanks bud! i appreciate the tips!

avalon42

iTrader: (1)

Well, that FIPG is not working (leaking in an area), so I'm going back to Kragen and getting a kit so you can cut out your own gasket. That's probably better and will seal better than the FIPG. Omarg, don't listen to me. I'm a complete nut.

91LS400LEX

I dont know because my tach isnt working properly. Sometimes at idle when the engine is at full operating temperature and in gear its almost down on zero.

I drive my car easily, but I rarely see it above 1900 rpms.

avalon42

iTrader: (1)

Funny you mentioned it. A day after I did the repairs, this problem showed up. The IACV went bad, seized and would not actuate. It wasn't actuating like it's supposed to, so I had a ridiculous high idle (2000 to 3000).

I almost want to say it was because of my liberal spraying of carb cleaner into the unit. I read on another forum to use an O2 safe cleaner+lubricant that Valvoline makes. This makes much more sense after I took it apart

Luckily, there are a ton of old LS400s in the Pick A Part lots. I picked up a used IACV for $16, even came with a new clip (well, used clip that wasn't broken and brittle to hell like mine was), so I spent time picking out the pins and locking them into the new clip harness.

So the idle is like new, but it did not fix the overall problem, which is the dip in RPMs when the AC is engaged. I think it might be a grounding issue on the compressor itself, and was searching for an elusive idle up circuit (which doesn't exist on these cars to my knowledge) and will delve into it tomorrow morning. I'll post an update then. BTW, the TPS only controls the idle. I do not want the idle to be on high all the time, I just want it to idle up on load, like when I engage the AC Compressor.

avalon42

iTrader: (1)

Well, I answered my own question. There were several things that were wrong. The tensioner pulley bearing was going out, so it was dragging down the whole drive belt. I replaced that, and the engine was immediately more responsive. We couldn't really tell it was going bad until we put a scope to it and listened closely.

The noise from the compressor itself was due to not enough oil, and as soon as we added the 2 ounces of ester oil, it quieted nicely. I'm using that Freeze 12 (R12 substitute) and after 2 cans of that, A/C is manageable cold. Yes, I know about some of the compatibility issues brought up for using the stuff, haven't had a problem with it in the last 3 years or so.

There is no idle up valve. This function is built into the air conditioning control unit which sends the signal to the ECM and puts the idle up.

Viola. Working like clockwork now.

python

iTrader: (4)

nice work!