97 corolla check engine light on

[GKK]

My sons 97 Corolla was running very smooth until I replaced the air filter with a K&N. A day later the check engine light came on and the engine (1.8L) started to idle rough.

I was going to clean the MAF sensor but, found that the 97's didn't have one.

I have installed K&N air filters in all of my other vehicles with no problems. I appreciate all suggestions and advice. Thank you for your help.

[GKK]

Update:

Today, I went to AutoZone and borrowed their code reader. There was only one code which was P0304 (cylinder 4 misfire).

I'm going to replace the spark plugs and wires but, could there be something else causing the cylinder 4 misfire. Thanks

[Dr Tweak]

There could be. Try that first and see what happens.

-Doc

[GKK]

Thanks, unfortunately my the car was stolen form my driveway this morning.

[Team High Rev]

did you get the car bck, and my light turns on too, all you do is disconnect the batery and it should restart the ecu, when you put an upgrade you should always restart it, because the ecu doesnt know what it has so when you restart it it can read it

[GKK]

Unfortunately I didn't get the car back yet. Also, I disconnected the negative battery terminal which cleared the code but, the check engine light always reappeared and the engine had a slight studder.

At least the thief got a car that wasn't running 100% yet.