Looking for advice on what my cars issue may be
Every morning when I turn my engine over, it does this. Revs up as desired, then revs absolutely flatline to the point where the car shudders and sounds like it’s about to stall, before revs kick back in again and it starts to level out. Does this EVERY morning (and if I drive in the evening after leaving it idle for hours, but the flatlining is less if its been in the sun). By the time I drive to work (about a 25 minute journey) the problem has subsided (if I turn the engine off and turn it back on again when I get to work, it just turns over and holds revs like its supposed to) it only does it when the engine is cold and hasn’t been used.
Have taken it to a garage where they cleaned out all of the filters and reset all of the electrics hoping that would be the fix, but it didn’t change things at all. When they plug in the diagnostic machine it comes back with zero faults on the system, and they don’t know what the problem is, or how to fix it.
Has anyone encountered this before and know what the issue is?
Car is a 2004 Ford Focus Zetec. Thanks