When I start up my truck, the truck will idle for about 2-3 seconds normal and then it will drop to a low 400-500 rpm rough idle and the check engine light will come on. Also, the battery gauge will swing to the right (drop to 9-10 volts). If I rev up the engine and hold above 1200 rpms, the battery gauge will go back to normal (12 volts). When it's warmed up, it's smooths out a bit, the idle will be at 600-700 rpm, engine light will stay on, and the battery gauge will go closer to 11 volts at idle but read normal 12 volts when I give it gas.
I have just had the head gasket replace, and water pump replace (they need repair). The above issue start about a month after these repairs. After the issue started, I had the battery replaced (it was old anyway) but none of the symptoms changed.

Any ideas??

1990 2.3L V6 XLT Ranger w/ 154,000 miles

 

[sm=welcomesign.gif]To start with you should go to a place like autozone to get the codes read for free.[hr]This way it would give us a better idea what is going on.[hr]Also when was the last time it was tuned up?

 

Sorry, tune up was completed same time as the water pump and head gasket. Replaced rotor, wires and plugs.

 

Well for now i would check the vacuum hose's for crack's or see if they are disconnected.[hr]Also check all wiring to make shure all plug's are on tight.[hr]I all else fail's get the codes read and post them here.

 

Will check codes and then post. thanks

 

Well, Autozone in Chicago is no help if you have a truck older than 1996. Had to go to a couple auto shops to find one that would be able to read the error on my truck. Murphy's Auto Parts were really nice and had no problem running the test a couple times to make sure. The code is 54. According to the book, ACT (air current thermistor). Sound about right?? Sorry told wrong....ECT (Engine Coolant Thermistor)

 

I popped the hood and located the ECT up by the top radiator hose on the front top of the engine. The thermistor was the issue cause when I touched it, it completely fell apart. My question is does anyone know how to get at the old thermistor to replace it. The space is so tight I can't get a wrench or socket in there.

 

my 1992 ranger did the same thing.
i replaced the o2 senser and it has been fine ever since

 

Were you able to change the sensor yourself or did you have to take it into a shop??

 

i did it myself with just a deepwell socket. it takes about 15 min. to do, very simple