ive had my 97 z28 m6 with 100k miles for about 2 weeks, about 2 days after i got it i noticed a bad miss with moderate acceleration, i changed plugs and wires and nothing changed now tonite my ses light came on and it runs great , no miss at all, any ideas?

 

running in open loop?

 

thtas what i was thinking how can i tell if my car is running in open loop and does this rule out an ignition problem?

 

Could be a number of things. Any enginge performance sensor(o2, maf, ect) that is going bad will give you poor performance from bogus readings. When the SES light comes on, the computer ignors the values from that sensor and the computer goes to a preset value for that device. That value is obviously better than what the sensor is putting out to the computer. Thus, your car seems to run better.

Get that code scaned to see what is causing it. Could be o2, maf, ect.

 

Harbor Freight sells a basic OBD2 scanner for $40 it will help you figure out which sensor the pcm is ignoring, which I agree is what is happening.

 

Open loop, set tables, probably either a MAF or an O2 sensor issue.

 

O2 sensor is my guess. My car actually ran better when the SES light came on too. I removed the O2's on both sides and the car ran great. With them, it would miss badly in closed loop.