My truck has a bad miss at what seems to be a steady speed,in 3rd or od. I can rev-up the engine a little with the brakes applied and get it to miss. The miss is constant and rythmic. I've checked the MAP sensor and the voltage seems to be in line. Although, when I use the 4-cyl. tach scale and a vacumm pump, the5,10,15,20in. voltages are all lower than they should be, but are consistent. When I remove the vacumm line from the sensor the truck idles very badly, but it runs down the road with only a VERY OCCASIONAL miss. Do you think it's the MAP sensor?
Any help would be appreciated, Thank You

 

Rick ,
Before you chase faulty sensors , have a look at the obvious ...Plugs , Wires , Dist Cap and Rotor . When was the last time they were looked at ?
Paul

 

 

THE TRUCK RUNS FINE WITH THE MAP SENSOR VACUUM
LINE DISCONNECTED (EXCEPT FOR THE IDLE).I HAVE
NOT CHECKED COMPRESSION, BECAUSE IT RUNS OK WITH
VACUUM LINE DISCONNECTED (BURNED VAVLES AND PISTONS CAUSE MISSES NO MATTER WHAT YOU DO).