The whole story:

I've had a tune up about a week ago and these are the things that has been done. I've opted for tune up since i had idling issues.

- Tappets adjusted (quite mode )
- Throttle body cleaned
- Intake Manifold cleaned
- New set of spark plugs

After this, I installed new H4 bulbs on my ride (100w/90w) No harness, no relays, no nothing.

Everytime I turn on the headlights and the air conditioning, the idle goes down (which i know is normal) but when I go turn the wheel, the idle goes down to 500 and car starts to vibrate. As per my assesment, the car vibrates only when I do this things and when the A/C and HL are not on, idling is a lot better.

Where do I start from here? What do I need to check / replace and how much would it cost me? TIA :