Revving on own, used to run rich, unplugged MAf sensor...intake problem?

[mikesmithis007]

So I've gone quite a few places and can't seem to fix my explorer. Not looking for a miracle, but though I'd share it's history with you guys and see what happens!

One day out of nowhere, my '93 XLT started revving from about 500-1500 over and over again on its own. Only time it would stop is if I got going to about 20mph with gas. Ran super rich, blew black smoke and smelled terrible.

First OBD reading said bad O2 sensors, replaced all of them, no change. Then we took it to a shop that unplugged the MAF and it started acting somewhat normal again. So we tried cleaning the MAF but to no avail.

So now it's been putting around with the MAF unplugged and it's driveable. HOWEVER, when I put it into reverse, it usually does the whole crazy automatic revving thing again, until I put it into drive.

I'm lost, because lots of sources say it could be a huge number of things that cause it to act the way it did.

ANY IDEAS OR ADVICE IS GREATLY APPRECIATED!

 

[Roadrunner777]

Here are some free things to try:
1. There is a plastic duct from the MAF to the throttle body. It has to be air-tight. Take it out of the truck, and inspect it carefully. There have been reports of cracks on the underside.

2. The MAF could be bad. Here are some tests: http://easyautodiagnostics.com/ford_maf/maf_sensor_ford_1.php (free if you have a voltmeter)

3. Check torque on the intake manifold bolts, which you should do periodically anyway.

4. Check for vacuum leaks.

Here is the story: The MAF tells the computer how much air is entering the engine. A leak downstream of the sensor will mislead the computer into doing bad things. So, it starts guessing on the fuel injection, and you get the oscillations while it is trying to figure out what to do.

If you have a fuel pressure gauge, it would be nice to validate the fuel pump and regulator. Honestly, if you own an exp, you should own a code reader, fuel pressure gauge, and voltmeter.

I hope this helps! I'm betting softly that there is an issue with your MAF. It's a cheap junkyard part, and I would not blame you if you replaced it just to see what happens.