99 I30T "Service Engine Soon) issue

[I30owner]

Hello

I have a 99 I30T that has approx. 110K miles. The car has been great, requiring very little maintenance over the years, however, recently the "Service Engine Soon" light came on. I didn't notice any problems driving the car but I went ahead and took it into a tuneup shop to have it diagnosed and a tune up done on the car. I never had the spark plugs replaced before because the car had been running well. The mechanic indicated there were two diagnostic codes (random misfire & knock sensor). They recommended replacing the spark plugs should fix the problem so we went ahead and had the plugs replaced with platinum plugs. It seemed to fix the problem but after approx. 500 miles the light came back on. I took it back to the mechanic but he can't definitive tell me what is wrong. He thinks maybe the knock sensor is going bad. Rather than letting him shotgun the problem, I am thinking about taking it the a dealer and paying to have the car checked out. The car runs great but I imagine I will need to get it fixed before I have to have it smog checked again. Does anyone have any suggestions on what might also cause these symptoms?

[VA99Q45]

What were the codes when the light came on the 2nd time?

Changing the plugs may have fixed the misfire. Maybe you need to change the knock sensor also.

[I30owner]

Thanks for the response. The specific diagnostic codes were:P0325 (knock sensor)1320 - (ignition signal)

[VA99Q45]

You are getting the exact codes after the spark plugs changed.

If you changed the spark plugs and still get the P1320, then you may have a bad coil pack.