2011 Tahoe/5.3 issues idle random misfires

[Witzel2023]

Hello, I’m new to the group. I’m having issues with my 2011 Tahoe 5.3 flex fuel.
I had lifters bad on passenger side so I changed them. While I had engine apart I installed new melling timing chain kit, rockers new OEM lifters for AFM & ac delco roller lifters. Put new water pump plugs & wires. Took cats off put new muffler with the mini cat elbows that go into the O2 port. My wife drove it local 1st 100 miles, then took it to town 45 min trip drove perfectly once we got there before leaving it started misfiring at an idle but not horrible. Drove it home scanner showed heated O2 sensor so we replaced them. Then it started showing the P0300 random misfire on all them on live data. Still can’t get it to go away. Changed cam crank temp mass & map sensor. Got coils ordered trying that next. I’m lost I’ve done a lot of mechanic work over time & im puzzled. I’ve tried to glance over all my wiring but didn’t see anything that looks bad. I’m only off on weekend so I’m try to take intake off & see if maybe the gasket got pinched or something.
The Tahoe runs great when driving only at idle does it do it. Any suggestions?

 

[Geotrash]

Hello, I’m new to the group. I’m having issues with my 2011 Tahoe 5.3 flex fuel.
I had lifters bad on passenger side so I changed them. While I had engine apart I installed new melling timing chain kit, rockers new OEM lifters for AFM & ac delco roller lifters. Put new water pump plugs & wires. Took cats off put new muffler with the mini cat elbows that go into the O2 port. My wife drove it local 1st 100 miles, then took it to town 45 min trip drove perfectly once we got there before leaving it started misfiring at an idle but not horrible. Drove it home scanner showed heated O2 sensor so we replaced them. Then it started showing the P0300 random misfire on all them on live data. Still can’t get it to go away. Changed cam crank temp mass & map sensor. Got coils ordered trying that next. I’m lost I’ve done a lot of mechanic work over time & im puzzled. I’ve tried to glance over all my wiring but didn’t see anything that looks bad. I’m only off on weekend so I’m try to take intake off & see if maybe the gasket got pinched or something.
The Tahoe runs great when driving only at idle does it do it. Any suggestions?

My first guess is a vacuum leak since you had the intake off. Any codes?

 

[Foggy]

If you replaced the DOD lifters with new Stock Ones, You should have replaced
the VLOM at the same time.... A bad VLOM will cause lifter failures

 

[B-train]

What are the mini cat elbows? Is this a cat delete sort of thing? If so, you may need some sort of tune to make the ECM happy

 

[iamdub]

Hello, I’m new to the group. I’m having issues with my 2011 Tahoe 5.3 flex fuel.
I had lifters bad on passenger side so I changed them. While I had engine apart I installed new melling timing chain kit, rockers new OEM lifters for AFM & ac delco roller lifters. Put new water pump plugs & wires. Took cats off put new muffler with the mini cat elbows that go into the O2 port. My wife drove it local 1st 100 miles, then took it to town 45 min trip drove perfectly once we got there before leaving it started misfiring at an idle but not horrible. Drove it home scanner showed heated O2 sensor so we replaced them. Then it started showing the P0300 random misfire on all them on live data. Still can’t get it to go away. Changed cam crank temp mass & map sensor. Got coils ordered trying that next. I’m lost I’ve done a lot of mechanic work over time & im puzzled. I’ve tried to glance over all my wiring but didn’t see anything that looks bad. I’m only off on weekend so I’m try to take intake off & see if maybe the gasket got pinched or something.
The Tahoe runs great when driving only at idle does it do it. Any suggestions?

You sure them plugs are good?

I'd think that if it were AFM related, you'd just have misfires on the four AFM cylinders. But, maybe not necessarily. Yours, being a 2011, should have the updated VLOM already. Doesn't mean it's not faulty and possibly the cause of your original and possibly current AFM failure(s).

 

[Fless]

After replacing either the cam or crank sensor, a correlation procedure needs to be done. Not doing it can cause random misfires, just something to make sure it gets done.