Rough Idle 91 Ranger

I have a 91 Ranger, 3 liter. I have been having a problem with a rough idle. I checked the web and noted that it could be caused by a MAF sensor problem. What is strange is that I
have both a MAF sensor and a MAP sensor. At least I think I do. The MAP sensor is located on the passenger side firewall. It doesn't have a vacuum line running to it. The port on the MAP that the vacuum line would attach to, has a round grey piece of plastic on it. This prevent a vacuum line from being attached. The MAF sensor is in-line between the air-cleaner box and the throttle. So I have two questions:
1. Why would the engine have both a MAF and MAP sensor? 2. Should the MAP sensor have a vacuum hose attached to it?
Thanks!
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Jim opined in

It's a BAP sensor.. same basic sensor but measures Barometric (Atmospheric) Pressure
Because the computer knows the mass of the air going into the engine, it also wants to know what the environmental pressure is to balance the equation

I think you know the answer to that one now.
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Jim opined in

Where was that site?
Maybe after a lot of OTHER things are ruled out.
What do you call a rough idle?
Is it missing.. or is the idle hunting?
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That is a BAP sensor, same sensor as a MAP but does not read the manifold pressure but the pressure in the atmosphere. The reason is that for the processor to be able to calculate mass it needs to know the volume of the air entering the engine ( corrected for temperature ) and atmospheric pressure. The MAF gives the corrected for temperature volume of air going into the engine. With the two readings the processor then compares a chart that is part of the computer program. The processor uses the chart to determine what the total mass of the air is.
You need to look up TSB's. There is a TSB on the Ranger 3.0 engine rough idle, at about the same year as yours. It is a normal condition, and can not be repaired. The engine has a slightly hot cam as compared to the car version of the same engine is the reason.

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Thomas Moats opined in

Which makes that rough idle a GOOD thing! Or so many would think.
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A warning to you. My old 91 3-liter, now deceased, started out rough idling and ended up blowing a head gasket . Appearantly the gasket blew between two cylinders and that caused the rough idle, in a couple days it ate through the gasket enough that it hit a coolant channel and that was pretty much it. It was my sons college car and the gasket blew on the highway, a ways from anywhere, as luck would have it.

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