I have a 2003 Ford Focus LX manual and within the past week it began to slightly rev up or idle higher while driving, shifting, or sitting at a red light. This problem has been intermittent! Seems to do this more when the roads are wet.
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faulty oil pressure switch (cheap), worn oil pump (not pumping enough oil at low revs) but most likely worn shells or crankshaft (allows oil to pass too quickly lowering oil pressure - just not noticable when the engine is reving 'cos there's a lot more oil bieng shifted by the pump)
if you have 14 volts or more at the battery at 1000 rpms, the battery & alternator are fine. If you get the same surge when you turn the bower motor on high speed, it is just the normal load on the alternator as it puts out more current. The engine is supposed to compensate by kicking up the idle. It does this through the IAC, idle air control. You may need to clean the IAC passages and the throttle body passages. I also would clean the MAF sensor heated wires with carb cleaner or MAF sensor cleaner. The MAF is in the iar intake hose and has a 2 or 3 wire connector going to it. The heated wires are in the air stream. Then disconnect the battery for 2 hours to clear the "Keep alive memory"
It will relearn after you drive for 10 miles. May run rough for that time.
A flashing light is BAD. Its damaging the cat converter. I would check or replace the spark plug wires ( if all OK, then) replace the coil pack. I would not replace anything unless they test bad. but these car are known for bad coil packs.
mcdevito75 here, Sounds like the idle speed motor, Ford is known for these idle speed motors going bad, in the later stages the car races like crazy. have your repair shop check this idle speed motor and change it.
Taking a shot at this, I'd replace the thermostat. If it is partially open at idle it would allow enough coolant to pass through, but at higher revs, that slight allowance may not be enough to keep the engine cool.
It's inexpensive and easy enough to replace.
I hope this helps... Good luck!