I have a 1991 Montero RS 3.0 AT 196k

I am getting crap for gas mileageà roughly 11mpg, not more than 250 miles
From a full tank.

My last Montero was a 90 w/ 3.0 AT with 189k on it and I was pushing
21-21mpg! That was mostly highway driving but I hardly think that is makes
A 10mpg difference.

Any thoughts?

The first thing I'd be looking at is the maintenance history - when were the plugs, wires, cap, rotor, oil & oil filter, fuel filter, and air filter last replaced? Is the ignition timing set properly? Are the tires properly inflated? If all of the above have been addressed, then you would start looking at more unusual causes - coolant temp sensor, dragging brakes, transmission or transfer case issues, sticking distributor advance, clogged catalytic converter, etc.

...and welcome to the Wire! <img src="/forums/images/graemlins/smile.gif" alt="" />

If it's cold it could be stuck running in cold mode-Not warming up enough.

Which can go back to maintenance. Thermostat, sensors, etc

ECT for ECU is bad, and engine thinks it's cold all the time. To diagnose, smell the exhaust after the engine warms up, and it will smell like gas. Engine is running too rich by a bunch.

On thermostat neck terminals pointing forward. Terminals in a T configuration. About $30 at the auto parts...

I got similar mileage out of my 2nd Raider after I bought it. After a quick tune-up consisting of cap, rotor, plugs, wires, oil change, and air filter, it nearly doubled my mileage. The previous owner had 3 different brands of spark plugs in there; all gapped incorrectly of course.

Well I have replaced the ECT... and will be doing the plugs & wires in a few days. We'll see how that does.

Also, half of my daily drive is highway driving and my OD is out, so thats not helping either.

I tried to replace the temp sensor for the trans but I cant find one ANYWHERE! Even the Mitsu dealer acted like I was from another planet.

On the other hand I noticed that the temp sensor never makes it towards the middle... and I wonder if a previous owner put in a non-OE temp thermostat?
I think OE is 190* and I have seen some marketed for the Monty at 160*... could it be that simple?

Happy to be here, and happy to be back in a classic Montero!

could be...

ground the smallest sender wire on the water neck and see if you get o/d, and check the shifter switch...

I'm in the same boat with milage and a fast idle. I haven't been on here for awhile, getting Christmas $$$ overwith and avoiding getting wrtenching fever on thewire...
I picked up a new 195 T stat today. And the wrong temp. T-stat can make a big difference. Especially when it comes to passing emmissions test.
I have a H2O sensor coming Wed.
If that doesn't do it ,,,it's on to the ICS...