I've had a few problems hit me at once. I have a 94 Sc400 and the first problem was the plastic water outlet coming off the thermostat broke into several pieces and leaking coolant. I replaced the water outlet and lower radiator hose and fixed the coolant leak.

The second problem I had was the mass air flow sensor went bad so I replaced that sensor.

The third problem I am having is the car will not start and will not idle unless I give it gas and hold it steady. But, when I take my foot off the gas it will stall out immediately. Which leaves me to think its just a bad idle air control valve.

I think there's a really good chance that it's the idle air control valve. I'm just worried that if it isn't the idle air control valve, I'm not too sure what else it could be. I know the fuel pump relays commonly go bad on these cars. Since the engine idles smoothly when I hold the rpms at 1000 or 1500 rpms that should rule out the ignition components.

Do you guys have any ideas other than the idle air control valve as to what else it could be that would cause the engine to not start and stall out unless the gas pedal is applied? I know for a fact the mass air flow sensor that I replaced is a good part.

 

the engine isnt idling if you are holding the gas. i dont suspect a fuel pump relay because it does run when u hit the accelerator. im leaning more toward the IAC valve. do you have access to an Ohmmeter, or digital mulitmeter to test the IAC for resistance?

 

from alldata: INSPECTION

On Car Inspection


Inspect Idle Air Control Valve for operating sound. Check that there is a clicking sound immediately after stopping the engine. If operation is not as specified, check the Idle Air Control valve, wiring and Engine Control Module. Refer to Non Trouble Code Charts; Idle Air Control Valve Circuit.

 

Yes, I have a multimeter to test the iac valve and the lexus books for the testing and specs. I also have a spare iacv i picked up a month ago, just havent had time to swap it out. I dont remember hearing the clicking noise. So I think its the iacv too, I just wanted to see if anyone had any ideas. Since it seems to run ok when I give it gas, that should rule out quite a few things. Thank you for your response.

 

Fixed my car this morning. Turns out it was the idle air control valve causing it to not idle. So its fixed now. It was a trifecta plus one. I had the plastic water outlet that comes off the thermostat housing crack which caused a large coolant leak, a faulty mass air flow sensor and a bad idle air control valve all at the same time. Talk about bad luck. Also from trying to repeated starts with no success it wore down my battery from 12.5 volts to 4 volts. The battery was only 6 months old, but I guess the cold weather didn't help it either. Advance Auto did a slow charge on it for 4 hours and brought it back to life. Thats the third mass air flow sensor and third iacv i've put on the car. Each time it was replaced with a "good" used part, but im not complaining at all because both lasted for about 4 or 5 years and it still beats paying 900 for a new maf sensor from lexus and over 500 for a new iacv. Thanks for your help again.