JRad405

Is your car on a stock tune? I just had my TPS go wild on me and throw my car up to 2500 RPM while in park. I just put my car back to stock and the TPS just reset and the car drives normal now.

OP, your car has coil over packs so they probably look a little different from most spark plug wires. They are right under your fuel rails.

And have you confirmed that you really do still get crummy fuel mileage still (looking at your needle drop doesn't confirm anything)?

stanglvr38

Yes, I have the stock tune. I've also confirmed by gas mileage by dividing the number of miles by gallons used. Is it possible that a Coil on Pack could be bad without a CEL?

DRAGUL

Yes it is possible that a cop can be bad without throwing a CEL. In my experience the cop was intermittently firing. And you could feel the engine misfire while you are driving. It finally threw a code when it failed for a longer period of time.

cliffyk

Here is how the misfire detection works. It monitors the angular velocity of the crankshaft, and has nothing to do with direct detection of spark, fueling, or any other engine control parameter.

chasen1982

Im pretty sure your 03 mustang doesn't have spark plug wires.. it should have coils.. And i could be wrong but i dont think bad spark plugs will throw a CEL... You will have to ask some of these other guys.. But I dont think u have to replace the coils as often as u would a spark plug wire. (could be wrong tho)

stanglvr38

Chasen1982: Is it possible that a spark plug could cause your fuel economy to drop to 9 mpg?

stanglvr38

So I took out my intake and I took a a rag and cleaned out the plenum. Then, I went into the throttle body and opened it up. I stuck my finger in there and dragged it along the surface. When I took my finger out, it was black and wet. Is this normal?