Our 240 after start ECU confused for 15 -60 seconds and then seems to run fine. Has anyone been through this before?
Starts right up hot or cold! Just seems confuse for a little bit -
Help.
Russell

 

"Confused"? What do you mean? It doesn't know where it is? It doesn't recognize faces of loved ones? And why blame the ECU? May be it's the Johnson rod?

 

Good point!

Confused in as I understand it, the ECU receives data from numerous sensors. The ECU controls ignition & fuel according to what it is being told.

Car starts and runs fine, about 18 mpg.

After restart for approx 15-60 seconds the idle is a little rough and drops into a loop if I start to put in gear before the idle picks up and levels off.

Would thermostat being stuck open cause this? How about engine coolant sensor? What about thermostat in air box?

Engine will be idling rough and then looping and then you will feel something change and the idle will just purr....

Only happens on restart.

Thanks for any thought,

 

looping ? as in the idle RPM goes up and down rhythmically or what?

thermostat wouldn't affect this... a bad thermostat can cause either engine overheating (if its stuck closed) or taking too long to warm up (if stuck open).

engine coolant temp sensor (ECT) certainly can affect warmup operation, if the ECU thinks the engine is already warm, it won't richen it and it will idle very poorly until it actually is warmed up.

 

I have fixed my issue.........

It was a defective thermostat, when I took it out it was in two pieces both tabs that hold spring in place broken.

Engine never warmed up enough, causing runability problems with ECU getting wrong data.

Put in new one and it purrs............

Thanks to all who helped.

Russell
California

 

The ECU are very rarely at fault on these cars but when people are stumped it's easy to always blame the "computer"...

 

well, there was that one bad batch of early ECUs, I forget, 'pink label' ? yeah, 'pink label' -561's, from 1989-ish.

Engine ECU

 

'89-'90, apparently they're more moisture sensitive than other ECUs.

For both of my 240s I just pulled those thermostats out and never replaced them, corked up the hole on my first one with a camera lens-cover that actually looked pretty nice.

Latest ride still has the hose since our weathers quite cold, come spring maybe I'll use a jar lid.

 

92sedan; it sounds like you're talking about the airbox heat riser flap. I wire those shut. russell is talking about the coolant thermostat thats on the output of the water pump.

 

My bad, wiring the heat flap shuts a good idea too.