Rough Idle And Bad Mpg. Help

[ElliottU92]

I have a 99 Serria SLE with a 5.3 v8 vortex and it has a relly rough idle and i am getting about 8mpg on the highway. the code reader said mass air flow sensor, so i replaced it that didnt work so i replaced the map sensor and still not working. the message screen on the dash flashes low coolent also but my coolent levels are fine. has anyone ever herd of this

[wicked ace]

I have a 99 Serria SLE with a 5.3 v8 vortex and it has a relly rough idle and i am getting about 8mpg on the highway. the code reader said mass air flow sensor, so i replaced it that didnt work so i replaced the map sensor and still not working. the message screen on the dash flashes low coolent also but my coolent levels are fine. has anyone ever herd of this

You may need to look into why your PCM is getting a bad read on your MAF Since replacing it had no effect. Replace the Coolant sensor in your overflow resorvoir and the level message will go away. That is a common problem with GM vehicles of that era.