Have never run into this before. Using a Skunk harness and a chipped p28 in a BONE stock 99 SI. This was to be his first mod. As soon as we started the car we had a 1500rpm idel. Then it was 800, 1500,800,1500,800 and then all is right, dirve around and come to a stop, up down up down pefrect. Did try a stock P28, stock P30, P72 all with the same result. Plug in the origional and idel is fine. I have tried swaping the IAC for another and that had no effect.

Anyone out there have some insight????

And this will throw all for a loop. Took my own personal Skunk harness (using it now and have been for months) out of my 2000 SI, put it in the 99 SI and still got the same up down idel. All the harnesses and ecu's I have tried work fine in a 2000 SI but no combination seems to work in the 99 SI other than the stock OBD2 ecu. ?????????????????????????????? Help please!!!!

 

anyone have a thought???