would love help! 87 iroq w/305 engine. Replaced EGR valve, EGR solenoid, knock sensor, wires, plugs, rotor cap, spark ignitor, TPS (throttle positioning sensor), TSU (temp sending unit). Second smog test gives Fail for NO of 916 ppm (max 772) @15 mph but passes with 628ppm at 25mph. Have run 2 cans seafoam through. Stumped! Any thoughts?