Short thought.

What if the rough engine idle is caused by a bad temp sensor causing the engine to run on limited cylinders. Or even running warmer where the temp sensor is, versus where the gauge sender is. The engine is supposed to cut out cylinders when it starts to overheat.
Mine only does this when I'm at idle foot on break. Start to give it throttle and the coolant flow increases, and through forward motion air starts to cool the radiator.

Aren't there 2 sensors on our engines? One for the gauge(sender), and one for the computer I believe.

Again, just a short thought.

Mike Kievit

1997 F150 4.6l.

 

There are 2 sensors.

One is for the guage the other is for the computer. The one for the computer is the ECT (engine coolant temp) sensor. They are both mounted on the top of the engine block. The ECT has a grey body and the temp guage sensor has a black body. The ECT tells the computer how warm the engine is so it can adjust for rich/lean mixture.

If you want to test it, just back probe the sensor while the engine is warning up and check the voltage changes.

I still lean towards EGR flow causing the rough idle. Theory for me is that the EGR valve does not close completely as it should when you come to a stop and the mixture becomes too lean. When you step on the gas the presure closes the valve.

 

I think it would be much, much rougher with the coolant loss protocol running. But, that raises and interesting question.

Has anyone had the coolant loss protocol operating and can they comment on how the engine acts/power, etc. If not, do we even know it works. Some one should run the experiment for us.

Ok who wants to drain their coolant and drive 50 miles.

 

Good point Aj. I didn't think of that. Something to check though.

Tiger, We'll wait for your experiment and hear what you have to say.lol.
You would think that someone would have posted this before if it would have happened though.

MK

 

In 1997 my Block Heater blew out. Lost all the coolant. The truck runs on 6 cylinders. You will know when that happens. Check Engine light comes on. Engine over heat light comes on and the temp needle pegs. Engine runs like *****. It is the Cylinder head Temp sensor that tells the PCM to go into Fail Safe Mode.

Regards

Jean Marc Chartier

 

I had two coils go out at the same time on my 1999. You will know... it is a bad miss both at idle and while driving.... It is not just a rough idle......