So I bought a 98 blazer and im starting to hate it. I changed all thr plugs wires rotor and cap. Im getting 10 mpg and it runs rough when stopped in gear like at a stop light. Any ideas ?

 

First I'd go to advanceauto and get the computer scanned. Hopefully that will give you some guidance on where to start. There are a lot of things that can cause our trucks to act up like yours. The style of fuel injection GM used is problematic. Also the fuel pump, and distributor cap and rotor are touchy items on our trucks. And this is only parts... I'm not including all the little stuff that could be causing your problems.
But first, get it scanned. And then post back. If it just says "cylinder misfire" then it could still be numerous things. Vacuum leak,intake gasket, all the above that I mentioned. I'm not trying to scare you. But as with any other problem with a car... It's a process of illimination until the problem is found.
And I have to ask... Was the blazer getting this bad gas mileage before you did the tune-up?

 

another question is how do u know ur getting 10mpg? also is it lifted, alot of things can effect gas mileage.

 

It was getting 8 before the tuneup. I just bought it last friday. I did have it scanned. And it did kick back cylynder misfire on no 1 cylinder. And the other one was something about airflow. So I,gained 2 mpgs and its a little smoother.

Not lifted and going by the computer at the cieling of the truck.

 

the ceiling of the truck isnt always accurate only real accurate way is to fill it run it down and fill it up again and divide the miles you went by how many gallons to filled up with... Mine says I get 16mpg but I just got 23 mpg my last trip.

 

Noted for future thank u.

 

Well... The code that it gave you for the airflow. I'd look into it more. Have it re-scanned and the codes cleared and checked later again. If the airflow code is there again... it's a good starting point. The mass airflow sensor tells the computer how much air is coming into the motor. So that the computer can calculate how much fuel to add. I had an escort that the airflow sensor(actually airvane meter for it) go out. The car went from 36mpg to 13mpg and turned the back of my car black LOL! You can get some airflow meter cleaner(not carb cleaner!) from the parts stores. But I've always heard that the meters are touchy on GM's. If the codes is there still I would check the plug-in first. And then maybe get a used airflow meter and see if it helps. Does the truck have an aftermarket intake(K&N, Airraid) the oiled filters can cause the sensor to get dirty. Also if it had one on it before you bought it. The previous owner could have forgotten to plug the airflow sensor back in. But definately check the codes again and look into the sirflow code if it's still there.

 

use electrical contact cleaner and q-tips and GENTLY clean the MAF sensor, they look like little resistors and they get gummed up, also the egr valve is a good thing to clean as well, although those things probably wouldnt cause a misfire.

its a good idea to reset everything by disconnecting the battery for a while, and if the codes come back, then you know for sure you have problems.

 

Ok I will check these things out today. I sea foamed it wrong and now its wierd the check engine light is only on sometimes ????? It comes and goes as it wants and the stumble is still there. Oh and no aftermarket airfilter I did just replace the dirty one that was in it though.

 

ok so i went to the mechanic this morning and he did a fuel pressure check and that looks good. still throwing a random misfire code. i cleaned the throttle body and mass aiflow sensor and the sensor between the maf and throttle body and reset the idle to abot 900 rpms at idle. when the rpms drop so soes the oil pressure. when the rpms raise so does the oil pressure. it seems to be running a little smoother but not right. so where does that leave me now ?