Heya, I have a '95 Aerostar, big 6 auto (the "Van Cliburn"). Getting unusual hesitation (sometimes hard, sometimes soft) during driving at any speed, accelerating or at constant speed, but unpredictable. Sometimes the check engine light comes on sometimes it doesn't. When it does come on it then goes off as it seems the incident goes away. No predictable pattern. About 4 months ago had a TERRIBLE running problem after I replaced alternator...couldn't even go 10mph as if it struggled mightily (thought I screwed up the computer). Poblem then was corrected by cleaning the actual MAF sensor. I took the sensor out of the housing located on the air tube from air filter (notched the super-funky screws with a hacksaw to convert them to flathead screws for easy removal)...it is a very delicate platinum wire filament and it was a little dirty...cleaned it with carb cleaner. Ran like a dream. Until now. I repeated the procedure yesterday...no effect. My hand-held diagnostic code reader gives me the following: KonEoff 157: MAF voltage too low & 158: MAF voltage too high (I know...contradiction, right?). Then KonEon 116: EngCoolant Temp Sensor and 538: (no desc...always had that for last 2 years). Now about the Eng coolant...I replaced the thermostat some 2 years ago but recently developed a tiny leak so added a bottle of stop leak. Running temp bacame a touch hotter but I have noticed my temp gauge needle fluctuates between the o/r up to the beginning of the m on the curved word "normal"...it goes up and down as if a visual manifestation of my thermostat opening and closing. This has been going on some time so not certain it is related...but possible due to computer reading. First time ever getting that Eng Coolant Sensor reading, though.
Can anyone make sense of this nonsense? Anyone experience anything like this?
Help!

 

My temp guage fluctuates too, on both vans. Seems like it should be steady, but I guess it's just the thermostat opening and closing a little. I just watch to make sure it doesn't go too high, and it never does. Another of those things you learn to live with on an older vehicle.

 

check the connection going to the MAF unit, might be dirty,
disconnect the battery when cleannning the sensor
have you asked at a dealer for the 538 code, or even have them scan it

 

High There, The book says #538 means Operator Error, you have tomake sure to connect properly and hope youfind your problem