'99 XLT 3.0: Idle missing, problems above 60 mph

[nxne75]

My truck: '99 Ranger XLT, 3.0L, automatic, 170,000 miles. I've noticed over the last few weeks that the truck has been developing a small stumble at idle - like a miss here and there, maybe every 2-5 seconds or so. It's not actually too bad, sort of like a tiny hiccup.

But what has been worrying me is the fact that engine has begun breaking up at speeds over 60 mph, especially when I give it gas. If I accelerate over 60 mph, the engine will start to break up and miss and if I REALLY floor it after that, the breakup will actually go away, strangely enough. Once I let off the throttle and let it drop back down again (say below 60), if I give it gas again, over 60 mph it starts to do it all over again. Almost like giving it gas once it starts breaking up clears it out or something - I don't understand it.

Any guesses as to what might be going on here? I appreciate any input.

 

[rustybolt]

I'll take a stab at it.... Two area's to check. First, make sure the MAF is clean. Every time I change the air filter I will also wash down the MAF sensor with electrical contact cleaner, the type that doesn't leave any residue. Let it air dry and never touch it with anything. The second check the operation of the throttle position sensor in the throttle housing. In my experiences with fuel infected engines, if an engine sensor becomes flaky, that bad input to the PCM will cause the engine to run erratically. Bad input = bad output.