Hey All...
My 2003 STS is giving misfire code/SES light flashing... I took her to my mechanic friend at his shop, with good equipment/he's professional, don't worry. He said it was #2 spark plug, he took it out and it was all gross/black, number 4 was clean. He cleaned them both, cleared the codes and I drove her around town yesterday, without misfire / SES light... But of course, this morning, on my way to work, at 75 mph, the SES came back. I haven't run her codes yet, but I'm assuming it's the same P0300 misfire. Friend said if the code/light came back, I need to replace the fuel injector... (the cause of #2 / he says ) ...
Now, I'm pricing injectors, (cuz he'll let me buy the parts and provide them to him) and I read I should replace all 8.
What about the coils???
Advice please guys...

My 2003 STS is giving misfire code/SES light flashing... I took her to my mechanic friend at his shop, with good equipment/he's professional, don't worry. He said it was #2 spark plug, he took it out and it was all gross/black, number 4 was clean. He cleaned them both, cleared the codes and I drove her around town yesterday, without misfire / SES light... But of course, this morning, on my way to work, at 75 mph, the SES came back. I haven't run her codes yet, but I'm assuming it's the same P0300 misfire. Friend said if the code/light came back, I need to replace the fuel injector... (the cause of #2 / he says ) ...
Now, I'm pricing injectors, (cuz he'll let me buy the parts and provide them to him) and I read I should replace all 8.
What about the coils???
Advice please guys...