NucLex

I have a '95 SC400; daily driver, 140k miles.

I washed the car Sunday evening, backed it in the garage and it ran just fine.
Monday morning I start it up and the engine started oscillating from 1000 to 1200 RPM and back.
I shut it off, waited a minute and restarted...same situation.
Shut down again, pulled the engine ECU relay to reset the computer and tried again....same symptoms.

I drove to my favorite mechanic, told him my sad story and left the car.
He said diagnostics showed a bad "idle air control motor" and a replacement was ~$600 from the dealer.
I called all the Phoenix local dealer parts guys and they said they had never sold one and didn't have one in stock.

The car runs fine till I let off the gas or let it idle, then it starts "loosing it's mind" and reverts back to the oscillations. I'm out of my depth on this one.

Any control system savvy Lexus folks have any recommendations, suggestions, or a good used "idle air control motor" you are willing to sell?

Best Regards,
David Stricker

O. L. T.

iTrader: (17)

moving this to the ENGINE section.

Buttercup

The IAC could be clogged up with gunk. Try using some CRC Air Intake Cleaner or equivalent. My brother's pathfinder had a problem where he'd couldn't idle well and it would stall sometimes. He sprayed that stuff into the throttle body (following instructions too) and problem solved.

But your favorite mechanic says it's the motor so I wouldn't know.

motorheaddown

FWIW, the IAC is a stepper motor that allows air to bypass the throttle plate when it's closed at idle. I no longer own an sc400, but the IAC motor *has* to be located right next to the throttle plate. It's a part that you should be able to remove/replace yourself. Piece of cake.

A failing IAC is rare but possible. The fact that it's oscillating, however, tells me that it's actually working. If the IAC failed completely, you'd get one constant idle because the motor wouldn't move. It doesn't operate with position feedback meaning that it *has* to start at a known position evertime you start the car. If you turn the car off, do you hear a very quiet clicking noise? If so, that's the IAC getting set to it's known starting position for the next time you start the car.

I've had the same problem with my standalone EMS because of a rich or lean condition at idle. However, we can rule out the ecu because you disconnected it and restarted the car without improvement. It could be a bad O2 sensor providing bad AF readings to the ecu at idle. How does the car run otherwise?

Shoot, call your parts department and get a price quote for the motor. If it's the same part used on the Supra, you might get a good price from Curt Aigner on SF. Like I said you can replace it in 5-10 minutes.

-scott

NucLex

Thanks Scott, I'll follow-up.

LDS

NucLex

I found a used Idle Air Control motor at a local recycler ($200), had my favorite mech install it, and it made a world of difference.

When he took the old one off ,he took several resistances measurements across the electrical input terminals. The reading were supposed to be 30 ohms, but on (2) of the six pins it measured only 3 ohms. We checked the new (used) unit and it measured 30 ohms as advertised. He instaled the part, started the engine and the idle was a little high, but steady, then it settled down to 900 RPM.

Previously (old part installed) I noticed a hesitation just off idle on acceleration...now its GONE!

Another story with a happy ending.

Regards,
LD Stricker
Goodyear AZ

O. L. T.

iTrader: (17)

Glad to hear, but given the situation, it sounds like you shorted it when washing. i'd make a note of that in the future.

b1ackhawk

I was trying to follow this how to:
http://www.planetsoarer.com/IAC/iac.htm

but i have a little problemo.
My iac isnt exactly the same as the one in the pic (mines a 95 which is newer than this one) and the black housing on mine does not have the 3 screws on it. Doesn anyone know how to remove the black housing on a 95 IAC?

cmk228

my 98 es300 is oscillating but only every now and then/// used CRC to clean TB, Advance auto diano showed egr problem then man stated it could be the erg, or the iac, what shouls I do now?/////

VJ RC51

the idle motor is dirty and probably needs the bearings replaced. Do a search, tells you how to fix it. If you want the $1 fix. Reverse the innards of the idle control motor and put a longer screw in the throttle body adjustment and set your idle that way.

cmk228

so I should go ahead and buy a IAC?

VJ RC51

sure if u got 2-300 to spare.

cmk228

$149 autozone

cmk228

Thanks alot for the advise

rscott

it might not need to be replaced. local buddy of mine had the same problem. the IAC is right on the front of the motor. what you can do before you replace it is try cleaning it. start taking off the trim pieces until you get enough room to get to the screws that are holding it in place. unscrew it out and pull it out enough so you can get the plastic straw of a can of brake cleaner in there. go to town on it and try starting your car. it will idle rough and smokey until the brake cleaner burns off but it should help out alot. his car went from an extremely low rough idle to a perfectly smooth idle after about 10 minutes of work and $3 of brake cleaner. if that doesnt work then youll already have everything off to install the new one when you pick it up. post a picture of the front of the motor and ill draw a schematic up of what needs to be done. its pretty simple. good luck with it.


PS when you start your car hold your breath and get the hell out. the stuff burning up in the smoke will irritate your breathway. make sure you do it in a well ventilated area. keep the kids inside if you have any of those around and close all the windows and doors BEFORE you start the car.