Ford Focus 2004 manual 150K miles. Most days the car runs fine. Other days it will start and run until it warms up, then stumbles or hesitates at speed. When this happens the headlights and dash lights are also flickering. Sometimes i hear a clicking sound behind dash, left side. I have the sure cure: turn the heater fan to high. This works every time. When the engine is hesitating, i turn the fan to 4-high, the engine smooths out. Turn the fan down, engine again hesitates. Hesitates at 3, worse at 2, worst at 1. It seems to need the extra load. But after few minutes of high heater fan, the alternator light comes on. I flick the heater switch down, endure the hesitation for a few seconds, the alternator light goes out, engine still hesitating, flick the fan to high, engine smooths out.
A few months ago i could get it to fun smoothly with the fan on 3, didn’t need 4-high. Now seems to need 4.
On the days when it is always running smoothly, the heater fan can be on any speed, the alternator light does not come on.
Next few days or even weeks the engine will run smoothly, no hesitation, with the fan on or off or any setting.
The car has been to three shops in past year, one of them a major Ford dealer, who kept it two weeks. The problem has been diagnosed as battery (replaced), Battery connections (checked), plugs (replaced), fuel pump controller (replaced), fuel pump (replaced - ouch!), alternator (replaced twice - ouch twice), grounds (checked). Every time they “fix” something the car runs ok for a week or so.
OBD shows P2004 (intake manifold runner stuck) but all agree it can’t be the problem.
There have been a few times when i flicked the heater fan to high that all the dash lights died, fan went off, headlights off, turn signals didnt’ work, but the engine ran smoothly. Not so good on the highway at night!
There have been a few time, not recently, when the car wouldn’t start. No dome lights, no dash lights with key turned to ON, no clicking or starter with key turned to START. It acted as if my battery was missing. The cure was to turn the headlights on. All normal after that.