Hi guys ,
Why when i switch ac on the idle goes down to about 500rpm and don't go up to 1000rpm as usual?
Need help please.

 

When you turn on the AC the AC belt starts spinning off the crankpulley which sucks up some power from the crank. The engine needs to compensate for the power lost when the AC compressor starts to spin its belt. Its normal.

 

Thanks for your info but i know that you told me is normal,before i done the rebuilt it was like that but now remains low idle when i switch it on

 

It is not normal for the idle to fall down to 500 RPMs and remain there when the A/C system is switched on. It is however normal for the idle to drop a little and the ECU will compensate and you will idle higher than if the A/C system wasn't on.

May I suggest checking to see if all vacuum lines are connected or connected properly. That's your first step. The second step is to see if any CEL are thrown. Then I would do a compression check for all cylinders. When I stretched my valves I had a weird idle similar to the one you described. Also, right now, my car is doing the same and it is due to compression. I installed ARP head studs and I haven't gotten around to retorquing them. I know it's this because oil has accumulated between the block and the head. On top of that, I smell coolant.

 

Yep...Len is correcto. Whenever I turn anything on my idle goes higher not lower. That goes for the headlights, a/c, whatever...