I fought a stalling problem with my 240 but have made significant progress. replacing my clogged PCV system and my throttle body gasket made a huge difference and now the car stays running (and smoothly), except it still idles low when hot or cold. I can't tell how low since this one doesn't have a tach, but the idle is the same whether the car is warm or cold. The engine is responsive and the car runs great around town or on the highway, but the low idle bugs me.

I activated the mode #3 diagnostics and can feel the idle air controller switching, removed and cleaned the throttle body and idle air controller, adjusted the idle switch, cleaned the MAF sensor (and replaced with a known working one from my other 240, both work). I checked the intake piping for leaks, but couldn't find any.

Any ideas on what this could be? Could the idle air controller solenoid be activating, but not actually turning the valve? Or could this be a temperature sensing issue?

The car is completely driveable, but it's still not right.

Thanks!

 

when its fully warmed up, all electric accessories and AC off, unplug the electrical connector to the idle air controller, and the idle should drop (ideal is 500 w/o the IAC, and about 700-750 w/ the IAC). if that happens, then the IAC is functioning.

if you have a digital volt meter that has a frequency ('Hz') setting, connect it to pin 1 of the ignition coil (and black wire on ground), and the frequency you see times 30 should be your RPM. so, if you see 20Hz, 20*30 == 600, so thats 600 RPM (Hertz is cycles/second, and there's 60 seconds/minute and 2 sparks per rotation of the crank, so 60/2 = 30, that's why that's the multiplier).

 

another test of the IAC, remove it one of the hoses from it, hook up a foot or two of clear clean vinyl hose the correct diameter to fit snugly on it, run that DTM #3 diagnostic test again, and blow into that hose. when the IAC is cycling, you should FEEL the air pressure cutting in/out/in/out as the valve cycles.

 

Thank you Pierce.

Just got done with a quick oil change and trans fluid drain/fill and thought I'd test your first idea. When I unplug the IAC with the car running, the idle jumps up to what I would expect from a cold idle (sounds like about 700rpm). I don't have a multimeter with the frequency option, but the low idle sounds like 5-600.

I think my next step is to swap the IAC from my 91 240 and see what happens... It's nice to have two 240s around to check for blatantly bad parts.

Thanks again. Your comments are always very helpful.

-Chris