My 2000 I30 has 64K miles. A couple of months ago coil #1 was replaced. Recently, I noticed some rough engine idling in park(engine is vibrating as if a coil is bad) when I start the car. The rpms would go down quickly to almost 500 and then back up to the normal level and then in about 10 seconds the engine idles normally. There are no codes in the ECM, i.e. no MIL indicator. This doesn't happen every time I start the car but seems to occur on warm engine starts and again not evey time.
Now, a couple of days I started the car with engine cold and got rough idling that wouldn't go away. I also had an unusual smell coming from the exhaust. After several seconds I got P1320 and P0303 codes so my mechanic replaced the #3 coil.
I was hoping that my brief rough idling at starts would disappear but it is still happening. My mechanic tells me that if there are no codes, it's not the coil. Is he right? What else could that be? If the MIL is not on, there are definitely no codes in the ECM, right?