Questions and Answers

Ford Mustang Code 23 Q. Hello oh mighty one! I recently starting experiencing a misfire and surging / bucking in my 1988 Ford Mustang GT. The misfire occurs in all RPM ranges and engine temperatures, but is especially noticeable around 1,500 rpm. It is a 5.0 with a 5 speed manual, fuel injected, 113,000 miles, A/C, P/S, Cruise Control, no ABS.

I have owned the car since new, and although one mechanic told me "all Mustangs" do this, mine didn't for the first 111,000 miles I drove it.

Anyway, my problem now is that I am getting an error code 23, Throttle Position Sensor high voltage out of spec, even after putting two new ones on. I did erase the memory codes and disconnect my negative terminal to reset the PCM to the defaults. Is this an indication that my PCM is going bad, or is there some way I can check ? Also, if the PCM does need to be replaced, is that a difficult task ? I see it is located behind my passenger kick panel, and besides a little difficult to get to, doesn't look like a monumental task.

For the record, I have recently replaced:
MAP sensor
EGR valve
Oxygen sensors (both)
Throttle Position Sensor (twice)
Fuel injectors have been flushed (twice)
Air filter
Plugs and wires are about 6 months old.
Fuel filter is about 6 months old. (Should the flow arrow point left when looking at the filter from underneath the car?)

Also, I haven't been able to detect any obvious vacuum leaks although this is difficult for me to check. Any insight you could provide would be sincerely appreciated. I feel like I'm in a battle of wits, and I'm an unarmed man!

Thank you!
Brad

A. First thing, the arrow on the fuel filter should point towards the engine and away from the fuel tank.

Now, you've replaced the TPS, but did you adjust it after you put it in? There are two types of TPS used on this engine, an adjustable and a non-adjustable type. There's a picture below. If your's is the adjustable type, and I'm almost certain it is, then you will need to have a Ford Dealer adjust it for you.