Dear heyu,

Hope you're well and stay so. To clear any transient problem, disconnect the negative battery cable clamp from the battery's negative battery terminal. This cuts power to the car and clears any transient malfunctions. NOTE: you will need the four-digit radio "code" to unlock the radio, if the radio is the factory-original item.

Wait 20 minutes and re-connect the negative battery cable to the battery. Tighten.

I'd guess that after this re-set, the engine should run as smoothly as it did, before the coil/amplifier swap.

If not, clean the wiring harness connectors to the coil/amplifier. An invisibly-thin layer of corrosion can disrupt a circuit. Corrosion acts as a resistor. So, the connection might allow current to pass up to a point, beyond which too little current passes, to maintain operation.

An aerosol corrosion-removed (Deoxit) will get into tubular wire terminals. Otherwise, take some very fine sandpaper form a tube, with the abrasive on the outside. Insert this sandpaper tube into the connector and twist a few times. That should remove enough corrosion to restore proper operation.

Hope this helps.

Yours faithfully,

Spook