*&%^%$% Idle Control Valve

[914lps]

:chairshot: I’m the same guy that posted about my Idle surging up and down from 1,100 rpm to about 1,800 rpm. I also posted about the Idle Control Valve (91 LS400), and the cost of replacing it, over $500.00 up to over $700.00!

Everyone pretty much agreed the surging was the valve. Also everyone said to take the valve off and clean it. No real instructions were giving for cleaning it.

I had to do a tune up, so I did that, and at the same time took the valve off to clean it. I’m not sure we are talking abut the same thing. The idle control valve is in the front of the engine. Almost dead center. It is black and silver (plastic and metal), held on with 4 screws, and has a plug going to it.

Anyway I took it off (in fact had a mechanic doing most of this work). The part that sticks into the engine was very black and dirty. We cleaned it off. Made it very nice and shiny in fact. This thing has a head on it that looks like a nipple for lack of a better example, then a spring, and a shaft, going into the metal housing. The spring, shaft and nipple are all metal. The nipple is welded to the shaft. The cover that the shaft goes though to enter the rest of the unit is metal and held to the plastic cover with 4 screws. It goes into the housing that holds a micro step motor (fancy expensive solenoid) We did not open it up. The mechanic (who knows more then I, said he would do it if I told him, but only if I promised not to say anything when we could not get it back together. He felt opening it would be a very bad idea). We put it back onto the car.

Idle is still surging up and down. I had to go to Los Angeles. I could take the Lexus as is, or my 4x4 truck. I did not want to drive the truck. It gets 6 miles to the gallon and tires are very loud. I took the Lexus.

I did try putting some Chem 12 Throttle cleaner into the gas (it is made to do that), before I left.

I then drove to Los Angeles. It was over 300 miles non stop, at 80 to 95 per hour. I was hopping the cleaner would pull off a miracle. No such luck.

This is how the car acts. Start it up cold. Idle stays at about 1,100 rpm. After 30 to 40 sec, idle does the surge thing. From 1,100 to about 1,800, then just keeps going up and down, up and down. This is with car in park or natural. Put it in gear with foot on brake car hold at 1,100 rpm.

Driving seems normal at high speed.

On the street if I keep my foot off the gas, car will slowly claim to an rpm of 1,800 (from 1,100) then drop like a rock back to 1,100, then start to clime again. Got to get this fixed! This gets the car up to almost 50 mph without touching the gas!

I will be in Los Angeles for a few days. I’m open to everyones help.

Can the idle control valve really be cleaned. Has anyone done it. Just exactly what did you do?

As mentioned in the original post, a mechanic in Havasue (not the one that helped me tune up the car and clean the valve) supposedly scanned the car to find out the valve was bad. But he wanted almost $1,000.00 to fix it.

Your thoughts folks…

[RFeldes]

Could be a vacuum leak. Mine did that on my ex wife's VW and it was a bad vacuum hose. Check all hoses especially near the throttle body.

[maxed_out]

Man I've seen this before.... also drove me nuts. Slightly different symptoms my 91 would surge and drop mostly during cruising. You could hold the accelerator constant and she'd just drop off abruptly. Ended up replacing the throttle postion sensor and re-setting its postion. I followed the instructions in the repair guide (the big one from lexus) and it turned out well. Smooth as glass. Hope this helps you. Good luck.

[cruznroadking]

I agree the throttle position sensor is the most common part to fail on the earlier LS & Gs models for idle related concerns. I would have someone pull the code from the computor to be sure you're not just throwing money away. LOL

[914lps]

Like I said it only happens when I'm off throttle, not on the throttle. Also the code was read and reportedly showed the Idle control valve. The car was checked for vacuum leaks.

[99lsguy]

you could be at a point where;

you buy a new one........but ask if you can return it unopened for a full refund within a week...

take the old one back out - and try to open it up and fix it - if not; put the new one in..........hopefully the old one can be cleaned and fixed and save you the $$$$. THis is last resort - that part is expensive!!!

There should be a way to check that motor/solenoid with a volt meter or something???

[914lps]

I have thought about that thanks, but the "best" way to see if that is it, is to pop a new part in and see if that fixes things. But if not, I've spent some major money. And I do not think I can return a new one of I did put it on the car, even if only for a min or two......

I'm going to call around and look into the cost of a "used" one if I can find one.

But I would love to hear from someone that has cleaned thiers.

[maxed_out]

If we're still considering the throttle position sensor (which I still suspect) then you need to know it can't be cleaned. I've seen a bad one fake out the computer which gives you a good code but you still have a bad part. The sensor is kinda like a dimmer switch inside if you ever had one apart. There are bands of wires in there that wear and get flat spots. I think they give a resitance reading back to the engine computer and that translates into its postion. It they wear it gives a faulty or intermitant reading confusing the cars computer and you can get the surge and other stuff.

As a suggestion, one fast way to eliminate the the throttle position sensor is to "adjust" it by loosening the screws and slightly turning it thereby changing its postion. Then try running it and see if it affects your problem. MARK the current position with a pen or matchmark so you can re-set to original position.

This was how I narrowed down elimated my problem even though the diagnostic computer said it was ok.