My truck has been having some issues lately whenever I first start it up and it starts idling down it will start to sputter and will drop down to like 3-4 hundred rpm and when I go to give it gas it back fires it used to just pop but today it back fired really loud. I was thinking it’s the fuel pump but it only does it when it’s cold but once it warms up it runs fine. I’m honestly clueless as to what it is

 

Sounds like it could be the Idle Air controller, but when you mentioned that it backfires, it makes me wonder if you have a very stretched timing chain in your motor. Has the timing chain ever been replaced? Lastly, are you getting a check engine light? If so, have you hooked up a OBD2 scanner to see if you are getting any stored or pending codes?

 

no but had to replace the seal where the timing chain is. And yes have ran a scanner it threw codes for my cats and misfire in 6,7, and 8th cylinder

 

Has your intake plenum gasket been changed? Take a look down the fully opened throttle body and see if you see any oil pooling in the bottom of the intake. How many miles is on the motor and when was it tuned up (spark plugs, cap, rotor) last? You can also try pulling off the throttle body and thoroughly cleaning it with special attention to the well in the rear where the Idle Air Controller piston sits.

 

no. It has 125k. Like 3 months ago it’s had the problem before we tuned it up it’s went through 3 sets of spark plugs.

 

That sounds like a clogged cat..... what do the plugs look like when you pull them?

Try taking the front O2 sensor out of the exhaust. Yes, remove it completely. (it will set a code....) See if it runs any better.

 

I do have clogged cats they’ve been clogged for awhile but unfortunately cannot get them off cause the bolts are super rusted. But the issue was way before it ended up getting clogged. I have no idea I haven’t pulled em sense the last time they were changed. If I’m not mistaken my O2 sensor is no good. But I will try that

 

Hot wrench for the bolts..... Either that, or a sawzall......