On my '89 F-250 with E4OD, the tachometer goes to zero at idle, and bounces a bit. Where is the tach sensor, and is there a TPS on this thing?
Thanks!

 

The tach sensor is located on the ip gear cover just to the right and behind the oil fill spout. It is the one inch nut with two wires coming out of it. You can remove it anc wipe it clean which might help it, but mot likely you need a new sensor. a Ford only item.
I'm not an auto guy so I can't help on the tps, other than I think it is on the throttle linkage.

 

I believe there is a tps on the E4OD trucks, but I think its called an FLPS(Fuel level position sensor). I'm pretty sure it's on the IP attached to the throttle lever.