In the last couple of weeks and not everytime I drive I am getting engine stumbling problem at low speeds or when I stop.The engine does not die though.It does not happen for highway driving and as I said not all the time.I have no error codes.Had all new coil and plugs and wires put in about a 10 months ago.At idle and when in park it idles fine.Mainly happens when driving 20 to 45 mph.Once it begins it stops when I go to a high mph.Any ideas.Thanks.

As a update I took the truck out for another drive.I went fast I went slow I pushed the truck hard and then just cruised around town and no problems what so ever. am really stumped as no error codes,the engine idles fine and there is no missing.I ran it up hills and down hills as I read where if it was a fuel filter or fuel pump I would have problems going up hill.Really do not want to have to take it Ford .I do know one of the techs there though and will call him on monday and see if he has any ideas.Anyone lese have any ideas on this??????????????????

I would of said IAC, that controls you Idle and can cause it to change you idle or rev and also stall when you let off the gas

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I plan on cleaning the maf tomorrow>is the IAT part of the MAF on a 99 ranger?Thanks.

yeah, i think

could also be the IAC valve. to test it all you have to do is unplug it while the engine is running if the engine stalls the IAC valve is fine.
the IAC valve is on the throttle body. just un plug the wires at the back of it.

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I unplugged the IAC and engine stalled so that looks to be good.I have not cleaned the MAF or IAT as of yet.This morning I drove to town which is 2 miles and stoped at the store .When pulling out of the store parking lot and coming to the stop sign the stuttering started to happen again.My speed was about 20 mph.I pulled off the road and turned the truck off and restarted and it was fine.I wanted to see if turning off the engine and restarting had any affect which it did.Not sure if that means anything.The problem went away so I went and had my fuel filter replaced as I am just trying to do the cheapest fixes before getting into anything complicated.After having the new fuel filter installed the first thing I noticed was it took less presure on the gas pedal to get the truck moving.I am not sure that makes any sense.I took the truck out on the highway and also noticed that I had more get up and go.I got off the highway after a few miles and did some in town driving and no problems at all.I also stopped at a few places and turned the engine off and let it sit for a few minuets to see if I could get it to sputter again and I could not.
As I have said this has been intermitant but the last few days has happend at least once a day.
So will let it sit over night and give it another try tomorrow.I am hoping that the fuel filter was my problem but I am not ussually that lucky.I appreciate everyones help and will post my findings tomorrow.Thanks.

Well drove around all day today and no problems.So keeping my fingers crossed that it was the fuel filter.

Well today it happened again.I thought I had the problem solved...hmmmm.When it happened I was in a drive through and the engine started to sputter and after about a minuet it was back to running fine.When I pulled out of the drive through I had my code reader with me and though there was no cil on I hooked the reader up and did a scan and it came up with PO133 PD (O2 Sensor Circuit Slow Response) .From what I read in the reader manual is that the reason it does not throw a CIL is that it has to happen X amount of times before it throws a CIL and clears itself after a certain amount of time.When I got home I checked the O2 sensor that the code was directed at and it had come loose from its mounting bracket.Not the 02 sensore itself but the electrical conector that clips to the motor bracket and the wires where laying on top of the exhast pipe.
Could this cause my problem?

That could be your problem. You still need to clear the computer though and the instruction that came with the code reader should tell you how to do that. The O2 sensor could be going out though. There are ways to test them which can be found in the Haynes manual I believe. I had a similar problem and after $1600 and three mechanics it was running rich and it was a bad solder joint in the computer which kept the fuel pump on even after the 5 second start up. I know, I spent too much trying to fix it, but at the time it was the only thing I had to drive. Tally's Garage in Jefferson Parish LA is the man.

Seems I may have fixed it by putting the wire connectors where they belong.I took it for smog yesterday and passed smog and problem has not returned.Fingers crossed.Thanks.

What IAT stand for?

Intake Air Temp Sensor