Changed Air Charge Temp Sensor

[rjc]

Now I'll have to wait and see if that will solve my intermittent rough idle with warm start up problem. My explorer was getty particularly cranky today so I started unplugging sensors. I started with the air bypass valve sensor and then mass air flow sensor both made the idle worse but when I pulled harness on the ACT, nothing, not change. The only difference when driving was that the check engine light was on. Otherwise it was performing as "normal". After replacing the new sensor and giving it a chance to warm up on the drive home from the auto parts, it seems to be running normally at idle. Not the smoothest engine but no worse than a friends 4.0 that I listened too a few days ago and actually mine sounds better. Since my problem was becomming more frequent, I'll let you guys know if this $12 part is the solution to my rough idle problems. It was a very easy sensor to change as it is right on top of the intame manifold behind the throttle and air bypass valve. These sensors have basically a coated looped wire with a bulbous end that's probably some sort of resistor. It looked bent and when pushed with a Qtip moved easily. I called 3 places. Napa wanted $27, Autozone $12 and Kragen $8 but it was not in stock. Long story short cleaning the MAF and Air Bypass Valves did not solve my problem. Hopefullly this will. rc

 

[rjc]

Promising

So far so good. I still was running a bit rough at idle today but I did not reset the computer. How long should I leave the batter cable off and what special things do I do when I hook it back on. Someone said something about letting the vehicle idle for some time. What's that all about. Thanks, rc

 

[Stephen S]

Take both cables off for about an hour...that should do it. Then connect them back up, crank it up and let it idle for about 5 minutes, then take it for a drive (a little aggressively) and then check your idle. I hope you've got it fixed!

 

[MikeP]

Your "Air Charge Temp Sensor" is called the "Intake Air Temperature Sensor" on page 6-16 of the Haynes Ford Explorer repair manual. For sure this is a fairly important sensor - but to be honest I do not recall seeing much said about this sensor. Perhaps this thermistor based sensor is a hardy difficult to damage part which rarely goes bad. It might need cleaning now and then. Nice post.
Mike with 91 XLT in Seattle

 

[410Fortune]

Rough idle =

dirty fuel filter
bad gas, or bottom of the tank
dirty IAC
dirty MAS
faulty 02 sensor(s)

vacuum or exhaust leak


With the early OHV 4.0L's the lower intake manifold bolts come loose. If you notice poor idle and have tried everything else check these bolts.
If they are loose I suggest replacing all the gaskets in the intake down to the lower intake.
Re-torquing the bolts may also solve the problem for short term.

Other symptoms include loss of coolant and increased oil leaks.