I replaced an injector in our 1999 Intrepid with a 3.2l engine... It was running on five cylinders, and threw codes 0204 and 0304... I replaced injector number 4, and the o-rings on the rest... I used a new plenum seal set... The car now idles fast like about 4,000 rpm against the governor, and the mixture is rich... It is running smooth on all six cylinders... There is now no codes...

 

Vacuum leak. Moving to the intrepid section......

 

The 3.2 and 3.5 (same engine) of that generation had thick paper lower intake gaskets that would crack and slide down causing a vacuum leak. It's almost impossible to see from the top side.

 

Thank you for your response... I did not mess with the lower manifold or gaskets other than to insert the injectors... I only removed the plenum and items necessary to remove the plenum... I did lift the fuel rail as well...

 

I am going to go ahead and replace the lower gaskets... I believe that heater tube o-ring on the bottom of the manifold is leaking coolant, so this will be an opportunity to get everything sealed up well... I may also do the head cover gaskets and seals while I am at it... I placed my hand over the throttle body intake hole while the engine was running at 4,000 rpm, it slowed a bit to about 3,000 rpm and kept on running, so air is getting in there from somewhere... I likely should have choked the engine dead or near dead by doing that...