Thermal Paste MAF
 

I had to remove my mass airflow sensor for cleaning on my 91 ranger 4.0, I noticed a white residue on the base where it screws to. Should I be using a thermal paste when I reinstall it?

You can, MAF uses an internal heater that's what 2 of the wires are for, but unless you are in Phoenix, AZ , 117degF outside temp it won't really be needed

Thanks for your help. This was the first time this was ever disassembled since I bought it new in 91. It did appear to have some kind of heat transfer paste. I squirted the sensor out last night, but it looks like my rough idle is caused by another problem. The OBD1, showed a 42 code which points to the O2 sensor.

O2 sensors are the ONLY sensor that wears out, 100k miles or 12 years which ever comes first

O2's use a chemical to detect Oxygen in the exhaust, too much oxygen is Lean, too little is Rich
And they simply run out of the chemical, its cooked away

But O2 sensor is NOT USED at idle or at WOT(wide open throttle), computer ignores O2 data at idle because idle needs to be Richer mix to prevent overheating and at WOT...........well fuel economy is not the point, FULL POWER is what driver wants at WOT, lol
O2 sensor is also not used until its above 650degF, which takes 4+ minutes after cold start, this is why O2's are HEATED to get up to 650degF as fast as possible

Rough idle on 4.0l OHV is usually spark related or dirty injectors
My 1994 4.0l OHV needs a can of Seafoam in the gas tank once a year to clean injector tips to get smoother idle
Over the year the injector tips get build up so at idle the fuel is dripped not sprayed so not a good mix and you get the random misfires at idle, when driving the injectors are open longer so spray out fuel and the air flow is much faster to get a better air/fuel mix in general

4.0l OHV needs Motorcraft or Autolite spark plugs, NGK are OK in a pinch
And gap needs to be 0.054, so a big gap
4.0l OHV is very hard on spark plugs, "eats" them as far as longevity, lol, which is why above brands are recommended
And only use regular copper or DOUBLE platinum,never single platinum, as it is a Waste Spark system, so single coating plugs will wear out the same as regular copper on one side of the engine
Single coating doesn't hurt anything, just a waste of money