'93 Yukon 5.7l K Fuel And Controls Tbi, Rough idle

[arkansasbowman]

purchased this vehicle 1 year ago and this thing was owned by older folks that took care of this thing to the "T". Every job, service, maintenance was detailed and kept. She has ran great from day one.

On Thurs I went to Wal-Mart at lunch and filled up with standard 87 grade Murphy Oil Gasoline. I usually use Shell or Exxon products because of convience for me. So anyhow I have heard of stories of described as bad gas. Not sure if that can be true, or what that might consist of but now I might just believe that I have received bad gas.

Like I said this 5.7L TBI purs like a kitten, seriously. But when I left work Thurs after my my fill up at lunch, I noticed instantly that she was now idling a bit rough, not terrible, but diffentanly not right, also I can feel it a bit while driving, kind of firing miss sensation. So I have 18 gallons of what we will call possibly bad fuel.

I thought the best thing to do is deal with the poor running until I can run this tank completely out. I figured rather wait till half full and inter-mix another gas product, then when I ran dry I would be starting from scratch. I did go ahead and replace the fuel filter last night and my assumtion that nothing would improve at that point was correct, still the same. Again it is not bad enough to where it would stall or considered terrible but certainly not right.

#1 question, am I doing the right by really doing nothing until the gas is gone? And can you truly get a tank of bad gas?

#2 I do not want to do too much to prove the theroy of bad gas this time, but I had been planning on changing spark plugs so I might do that, or should I just wait?

#3 Obviously on the 5.7L TBI there isn't much in the way of sensor, or if you will crap like all of the new stuff, it is pretty much Engine and Fuel induction and nothing more. But are there other things on the system that might go bad that control the Idle that I should look for or replace? I am used to so many sensor that the Diagnoitics picks up and replacing by that but again this does not have that to go by. Not sure if there is a Throttle position sensor or again just not sure what might else go wrong. Or should not just not get crazy over this until this gas is gone and new is in.

Again, Thank you in advance for any help

[maxwedge]

What exactly are the symptoms. if just a slightly rough idle, run the fuel down, if it persists with different fuel do a full scan, many things can cause this, vacuum leaks, skewed sensor inputs and the list goes on.

[arkansasbowman]

Yes, the only symptoms would be described as feeling of a slight miss, the idle isn't terrible but certainly changed right after the fill up was done and is not what it should be. Up to that point idle and acceleration were smooth as smooth can be.

I have yet to do any work on this vehicle myself as I bought it a year ago and other than oil changes she has purred since day one. Not even sure if a 5.7L K '93 year can be scanned is there a scanning port that say Autozone can hook up too?

Step by step I figure,

Run the gas dry, I did change the fuel filter but no change.

After a new gas and still running wrong is where I will start from.

I thought maybe just go ahead and put new plugs in, never can hurt I thought but would like too see is there any chance I truly, truly received BAD GAS, not even sure if that statement is possible or is it a myth?

From there Plugs, Wires(already new), Dis. Cap and Rotor, EGR, MAP, TPS
I did check over all the vacuum lines and they appear in great shape.

Like I said looking for direction or opinion what to do 1,2,3,4 etc. And not waste of bunch of un-necessary money


Thank you in advance

[maxwedge]

Anything is possible here, there is no quick answer, go by your plan, yes the truck is obd1 and all the sensors and codes can be scanned, port is under dash near steering column, AZ cannot scan pre 96 cars/trucks.