so i had my long tubes put on than i extended my 02 sensor wires the upstream pre cats i installed them all went well for a while, car had loads of power than all of a sudden it start to missfire pretty bad, idle ranges from 900 rpm to 5-600 rpm and while driving the car stutters and bogs out of power runs very heavy, the check engine light flashes occasionally i know its a missfire but i do not know where to begin i have p0300 code coming up random missfire my dumb freind decided to clear all the codes so know i cant even go back to them there were 2 others for the down stream 02's i beleive, any advice?

 

First thing is it is not recommended to extend the O2 sensor harness with out and actual plug to plug extension harness. Did you just extend the wires?

 

wait for the codes to reappear and then come back on here. WE will let you know what to do next

 

Check your plug wires

 

Also, if the headers were new and coated they have been known to mess up the O2s. Do a search on here I'm sure there is a way to pull them be able to tell if they got messed up by the header coating.