Just got Avic-d3 installed, no GPS signal on info screen, anntenna say OK, if I'm driving with info screen I see anntena goes to NOK for a second then back to OK. Bad anntenna or unit?

Could be either of those. Could also be bad placement. Where's the antenna located? how was the wire run? What kind of vehicle is it?

I run wire temporary to trunk and placed it outside, but still no signal, the car is clk430. That's driving me mad, before Avic I got car's original nav unit and it did had same problem, I thought its the anntena, so I got an other one still no signal, I figured its a bad unit and returned it, I desided to get aftermarket unit, bought AVIC-D3 and got The same problem. Is some black magic BS? Is this car cursed againt nav units?

Got to the bottom of the problem, the Merecedes teleaid system cause interference with GPS signal, as soon as cut power to it, everything worked.

Yeah sounded like there was something in the car generatin the interference. Glad ya figured it out since the guys I talked to about it were just as confused as I was.