so I recentely fixed my truck after doing lots to itbut when it wasn't running right i got around 18 mpg and now i get around 16 mpg.........when it wasn't running right I could smell gas wile driving it which made me think of Air system after changing everything fuel....so a new IAC valve fixed that but now i think the computer is thinking now that it's getting more air it can burn more gas..........is this a good hypothesis and if so can i change the fuel air mixture so it's not so gas guzzling?

 

Is there any difference in how you are driving the vehicle? Different outside temperatures? Different fuel station?

And no, getting more air doesn't necessarily mean more fuel. If it is running right and you are not driving around at WOT, the restriction is the throttle body which is what is controlling the incoming air.

 

The computer uses all the sensors to control fuel/air mixture to 14.7 ratio. Only way to change that ratio is to program the puter.

Verify your O2 sensors are hooked up. If the puter doesn't sense or the O2 sensor isn't working the puter will stay in open loop. That means it will run great, however your fuel mileage will suck. Could also explain a fuel odor out the tail pipe. Are you sure you fixed the original problem?

 

the original problem was, it was missing at idel and hesitating at high speeds (40-60 mph) at stoplights and stop signs it usually wouldstall after missing one or two times, but the new IAC valve fixed that problem, at least the symptoms. I know these blazer's don't get wonderful MPG but 18 sounds alot better then 16

and my driving habbits have pretty much stayed the same