lexdud

I paid the Lexus dealership $120 for a diagnostic. They told me that the IACV was bad as well as (possibly) the ECU. I have replaced the IACV and the car ran great for 10 minutes until the idle dipped. I turned the car off and then tried to restart it ... but it would not without the gas pedal being depressed. So now I am back to square #1. Now I am looking for a used (good) ECU ... but there are MANY different versions of SC ECUs. Lovely ... I am adding a final post just in case someone ever has the same no-idle issue. I finally solved my SC400 no-idle problem and this is how I did it: I bought a used, working replacement ECU. The dealer cost for the ECU is $1,500. I bought one on-line for less than 1/10th that. Just remember to get the same model number ECU as the one in your car.

I paid the Lexus dealership $120 for a diagnostic. They told me that the IACV was bad as well as (possibly) the ECU. I have replaced the IACV and the car ran great for 10 minutes until the idle dipped. I turned the car off and then tried to restart it ... but it would not without the gas pedal being depressed. So now I am back to square #1. Now I am looking for a used (good) ECU ... but there are MANY different versions of SC ECUs. Lovely ...

"... combined by carbon ..."? What do you mean? I cleaned the IACV and added anti-seize. So what is the solution?

Are you sure it's not a fuel problem? I am almost completely sure. The first time I start it after I remove/replace the IACV it will run forever (until the tank empties. I took the car to a local mech shop and they told me that they have no idea what was wrong with it ... but off-the-record would put bets on the IACV. The IACV is causing the problem ... but not because it is broken.

I would hope that the mods would allow this post to stay in the general forum as this venue will give this issue more exposure. Many have posted procedures to remove and clean the valve ... with most people reporting excellent results. BUT ... but what if the problem is and is not being caused by your IACV? I know it sounds strange but please keep reading below: II own a 1993 SC400 with 52,000 miles. A few months ago it would (every once-in-a-while) start idling very badly ... but this would clear up quickly by reving the engine to 2K RPMs for about 5 sec. Fast forward to 3 weeks ago ... the car runs ONLY when you give it some gas ... it will NOT idle at all. I just bought a used IACV to replace my unit that I thought had gone bad. I replaced the outer part (with the motor and (cleaned) valve but the problem persists. Upon the first start-up my car will run BEAUTIFULLY forever, unless you turn the engine off. Upon restarting it the engine will run very rough with an idle speed of about 300 RPM. Turning the engine off again and restarting returns the car to it's original state ... it will NOT idle and only does so when the gas is pushed. When I pull the IACV I always retract the valve so that it is in it's full open position when reinstalled. I believe that upon each subsequent start-up the valve is closing a bit until the 3rd restart when it completely closes ... and stays that way permanently. What I cannot figure out is why. I was hoping that those endowed with more knowledge of how this system works could help. I believe that I now have two working IACVs and that the problem is probably what controls the valve to open and close. In my ignorance I am going to assume that it is the ECU. Please chime in with any comments or advice you have. I do not like taking my car in for work as I like doing it myself. I am contemplating one or more of the following: 1) Taking the car into the stealership for a diagnostic. 2) Trying to find someone local to Orlando (UCF area) who has a '93 compatible ECU that I can borrow to check my theory. 3) Removing my ECU and sending it off to be repaired via a service I found on Ebay. Thank you for reading ...

Congrats on being able to determine what your problem is. Your ability to read the trouble codes off the OBD I port under the left side of the dash is dependent upon your check engine light coming on and storing an error code. Unfortunately, in my case I have a no-idle situation with my 1993 SC400 (52,000 miles) and the ECU is storing no codes ... NONE. My problem is the IACV ... or what controls it. I have purchased a second IACV but the problem persists.

is the CEL (check engine light) on? MAF is a good start, but if its not throwing a code then hold off on just spending money and changing parts. Get a scanner and pull the codes. Just because the light isn't constantly on does not mean it doesn't have any stored codes. Anyways, this is a good place to start. Let me know what you find out. you are correct, it is obd1. sorry must have been on the crack pipe hahaha! anyways just pull the codes with a paper clip. count the flashes of the check engine light and look up the code(if one is stored) Tried this last night to no avail. The CEL blinks at 0.5 sec intervals forever. I was told that either there are no stored codes and/or the ECU is fried. Any other suggestions ... short of seeing a mechanic? I have a 93 SC4 with only 52,000 miles and I am having problems as well. Unless I am mistaken (I've bee know to) both of our cars are OBD I and NOT OBD II. I have an OBD II scanner but it would be worthless on pretty much any car manufactured prior to 1996.

is the CEL (check engine light) on? MAF is a good start, but if its not throwing a code then hold off on just spending money and changing parts. Get a scanner and pull the codes. Just because the light isn't constantly on does not mean it doesn't have any stored codes. Anyways, this is a good place to start. Let me know what you find out. I have a 93 SC4 with only 52,000 miles and I am having problems as well. Unless I am mistaken (I've bee know to) both of our cars are OBD I and NOT OBD II. I have an OBD II scanner but it would be worthless on pretty much any car manufactured prior to 1996.

I have the same problem ... I have a 93 SC4 with 52000 miles. About 6 months ago the car would suddenly stall if you were driving and took your foot off the gas. Just the other day I started it and it died as soon as I take my foot off the gas. I did the following to diagnose the problem: 1) Removed and cleaned the IACV. My valve was near mint condition and clean. Not the problem. 2) Removed and test the MAF per the shop manual. MAF test OK. I now go out to my driveway, start the car right up, take my foot off the gas and watch it die immediately. I wish someone could/would provide an answer ... perhaps this has happened to you. How did you fix it. Good luck OP ...

Yep. The "stop valve" is a schrader-type valve. It is very close to the a/c compressor and has a black plastic dust cover screwed it place. If is has been converted from r12, the color code may be different, blue, etc. I remember it being a little tight in there and you have to watch out for a wire connection. Good luck. Thanks Dave, that's the confirmation I needed ... and it came only an hour after I posted this thread! What service ... You said: "It is very close to the a/c compressor ...", actually, it is located on the top of the compressor and yes, the schrader has a black plastic cap. I just wanted to make sure ... Thanks again ...

I have tried hard to locate the low-side (suction service port for recharging the A/C system on my 1993 SC400. I have an electronic Repair Manual with only one very small picture which shows it on the A/C compressor. The high-side port is so easy to find as it is right there sticking up by the radiator. Can someone with a good service manual help me confirm if this is, in fact the low-side (suction) port schrader valve and let me know. I have attached the page (AC-15) from the manual. Thanks ... AC_15.pdf

I am considering trying to add some refrigerant to my '93 SC400 that needs a bit of freon. I have an electronic (.PDF) manual that I got with the car when I bought it ... and the car itself. The manual fails to indicate the EXACT location of the high and low side service ports for this R-12 based A/C system. While the manual shows that the two service ports are on the left side of the engine (about 18 inches forward of the evaporator ... I have checked extensively and there are NO service ports there. I have run my hand all the way from the high/low of the compressor back to the evaporator without finding any ports. I have found one port at the compressor and what looks like a service port conveniently sticking up through a plastic cover on the front-right of the engine by the battery and engine fan fluid reservoir. Please, can anyone advise where the low pressure (suction) side service port is (the port used for recharging refrigerant)? A picture/drawing would be much appreciated ... if possible. Thank you for reading ...

Thanks .. that's what I thought. I found a sorry example of a '92 with a sunroof and my hair was barely touching the headliner. I do not need a sunroof so I guess I'll narrow it down to non-sunroof cars. Thanks for all the responses!

I do not yet own a Lexus but am actively looking for a mid-90s sc400. I was wondering if current and previous sc400 owners could help answer a VERY important question: How tall does a driver have to be before he/she is TOO tall to comfortably drive one? I am 6' 4" and currently drive an '04 Nissan Frontier. As tall as I am I have no problem in this small truck. So how is it in the sc400? If you own one ... how tall are you and if you are tall (6' 2" or better) how comfortable is the vehicle for us taller people? Thanks for all of your kind responses ...