I have a 1991 Dodge Dakota 4X4 extended cab with a V6 3.9L engine with 141,000 miles. A few weeks ago it began to idle rough and would often kill coming up to a stop sign. This lasted about 3 days and then it started running fine again, but ever since then my gas mileage has gone from 16-17 MPG to 12-13 MPG. I have changed the spark plugs with no effect. Any ideas?
Check and clean the throttle body and IAC valve.
You MAY also have a clogged fuel filter.
Thanks for the tips! Since posting I have also changed the plug wires, cap and rotor and just yesterday the EGR. We will see!
Blindly changing parts may or may not fix it, economically speaking.
A visual inspection of the plugs (how did the old ones look?) and time on an ignition analyzer to check the coil and ignition module. However, I think you would notice misfiring that dropped MPG 24%.
I would check for any vacuum leaks, loose vacuum hoses or electrical connectors, then get an engine compression test.