My 2004 Grand Cherokee has a long cranking time..

My Grand, cranks for a very long time . Finally , if you give gas it will start. Chrysler paid to have a full diagnostics run on it my Jeep dealer still could not find the problem. I told the person at Chrysler that it was kind of strange that we have the only 3 Jeeps that do this as they said they've never heard of this problem. After the diagnostics were completed they said that the only thing that they could "think" of was it needed a new throttle body.  I have not gotten one yet (mechanic said I could get one at a salvage yard for about 50 bucks and he told me what to clean it with). I haven't tried that yet. Has anyone else had this problem? If so, what was the remedy? Thanks