ChrisK

iTrader: (1)

London Bill,

Thank you for the info. My car is running fine now, but there is 40-50 F weather in Chicago right now, I will keep this in mind next summer when the problem comes back.

Thanks,

sorka

Sorry to resurrect and old thread, but several comments.

First, this used to happen to me as well. Right around 90K miles if you were coming to a stop and turning off your AC, the engine would die. Fortunately, I had a pretty good mechanic that diagnosed it as a sticking IAC valve for the AC. The price on that valve is about $1100 dealer retail. I'm sure wholesale is probably half that. At any rate, I was took it off and it turns out that it was coated with lots of carbon.

To make a long story short, the IAC valve wasn't sticking, it was very dirty. After dropping it in an untrasonic cleaner with carb cleaner for an hour, it was quite clean. After I re-installed it, it never died again....until just last week at 180K miles, but I think it's a different problem now.

Just a note on the way the ECU deals with this valve. A smarter program would realize that air flow is being restricted because idle doesn't change as it should when the valve is opened or closed, and then it would make semi-perminant adjustments. Unfortunately, the ECU just tells the valve to open or close a certain amount based on whether the AC is on or not and doesn't compensate for reduced airflow.

Now back to my other problem. My SC400 is sometimes dying on me when I come to a stop and I haven't just turned the AC off.

There are no codes.

The engine just dies. Any ideas?

RADSC

London Bill is correct.

My car stalled unexplainable on the freeway and streets. There was an engine code for the throttle body postion sensor. I replaced it. Within one week, car stalled again. I then cleaned the throttle body, and changed the plugs, cap, and rotor. Within one week, again, same thing----STALLED. I was going to give up and drop it off at the dealer. But, I read a thread where London Bill was stating possible Fuel ECU problem.

I takes 20min max to bypass the fuel ECU (a monkey can do it-- just two wires). Since then, about 2yrs--- no problems. This is probably the most COMMON reason for stalling.

The key is the fuel ECU problem is STEALTH( It throws NO ENGINE CODES). Running the diagnostic will NOT detect it. The dealer will not diagnose the problem.

I think it is worth your time before spending big bucks to bypass the fuel pump ecu.

PS, you do not necessarily need the fuel pump ecu. I have been without it for 2 yrs.

London Bill

An update on the fuel ECU bypass;

Someone has pointed out that by using the ECU bypass you disable the ability for the ECU to switch OFF the fuel in certain conditions such as "stalled engine", so if you had an accident which cut engine power and fractured a fuel line the ECU would be unable to shut down the fuel supply.

I think removing a built-in safety feature is not good and would advise you replace the fuel pump ECU if it is proven to be faulty, the FP & B diagnostic jumper should only be used to confirm the ECU is at fault and removed ASAP.

VSsc400

iTrader: (1)

anyone have picture and location of the IAC vavle?

thanks

dmurphy

My power/electrical loss is with a 94 SC400. It has completely quit (no power or electrical functions) at freeway speed (70-75 Mph) on 2 occasions and in town at lower speeds twice. The Lexus dealer says no malfunction codes are stored in ECU memory and their service people ran the car for 130 miles and couldn't duplicate the problem. Although I have not lost any fluid, the dealer says the power steering pump is leaking; however, the alternator (which sets directly under the PS pump) appears to be okay. I do have constant static on most AM radio stations which would indicate an electrical short somewhere. Occasionally, the antenna doesn't fully retract. The battery terminals are very clean so I don't suspect a problem there.

Does anyone have a similar problem and any suggestions on how to fix the problem.

Don

SupraCoup3

as far as the antenna, they die. the plastic gears get stripped and all you hear is a grinding noise as the motor tries to retract or extend the antenna...

...about the other stuff, you've got me. I'm waiting to see someone come up with an answer.

Also, make sure they fix the PS leak -- people routinely lose their alternators over that leak. Do a little search and you'll see what I mean.


John

London Bill

Don;

The fuel pump ECU can cause the engine to cut (amongst any number of things) when it first shows signs of "failing", happened to me twice on the same stretch of motorway (freeway) which freaked me out, but then it became hard to restart which is one of the telling points is as it gets progressivly worse is the engine refusing to start after it shuts down from hot (or after you stop for a short time).

I now understand why the engine cut at that specific part of the road, I had been coasting on a light part throttle (9v supply to fuel pump) and then accelerated again (this is because the feds have a regular speed check from the top of a certain flyover), the fuel ECU saw the demand for more fuel and tries to switch to High (12v mode) but the ECU gets stuck during the transition and stays "OFF".

Once the ECU has cooled down (sitting at side of road for 15/20mins) turn the key and away we go again with everything back to normal, second time it happened I inserted the fuel pump diagnostic jumper and the reluctant engine started first time, I then replaced the fuel pump ECU convinced that it was the cause of the mysterious shutdowns, during these issues I had no diagnostic codes presented to the OBDC.

The electrical systems present no warnings during all of this, all the warning lights come on in the regular mode with the ignition and the engine cranks over but simply will not restart until the fuel ECU cools a little.

dmurphy

London Bill:

Would the fuel ECU have any effect on the electrical systems? When my SC cuts-out at freeway speeds so does all of the electrical. It restarts immediately when I pull over, put the car in park and turn the key. It will then run fine for a period of weeks before the problem happens again.

Is the fuel ECU expensive to replace?

Don

London Bill

Don;

The fuel ECU failure will not be in conjunction with other electrical issues such as loosing all electrical power, this is more common with alternator failure (often caused by leaking PAS fluid on the V8 engines), bad battery or connections and the not so common breakdown of the body earth lead.

Fuel ECU is about £230GBP, I think they are around $300USD but it does not sound like yours is at fault.