Chasing a rough idle?

[dkad260]

I missed this thread, but @2009TahoeLT what plugs did you use when you replaced them? I hope the OE AC Delco as aftermarket can be very finicky.

Edit to add:

Do you have an aftermarket air filter, oiled? Have you replaced any sensors with non-OE sensors?

I didn't have the issues you do, but an occasional stumble and some slightly higher fuel trims. So with some down time, I had my injectors rebuilt and was surprised to see how bad the screens were.

I also went with new OE plug wires as well as OE plugs, new intake manifold gasket, and OE upstream O2 sensors. All this really evened out my fuel trims and returned my lost few MPG's. To keep everything in check, I also replaced the MAF and MAP sensor with OE.

Pics of my fuel injector screens at approx 150K miles.

 

[2009TahoeLT]

I missed this thread, but @2009TahoeLT what plugs did you use when you replaced them? I hope the OE AC Delco as aftermarket can be very finicky.

Edit to add:

Do you have an aftermarket air filter, oiled? Have you replaced any sensors with non-OE sensors?

I didn't have the issues you do, but an occasional stumble and some slightly higher fuel trims. So with some down time, I had my injectors rebuilt and was surprised to see how bad the screens were.

I also went with new OE plug wires as well as OE plugs, new intake manifold gasket, and OE upstream O2 sensors. All this really evened out my fuel trims and returned my lost few MPG's. To keep everything in check, I also replaced the MAF and MAP sensor with OE.

Pics of my fuel injector screens at approx 150K miles.

View attachment 470747

View attachment 470748

I originally replaced the plugs with ngk coppers. Just recently replaced those with ac delco iridium I think. I haven’t torn apart the injectors but I did spray cleaner through them to check flow and clean. I have replaced with ac delco wires, 4 coils, metal upgraded intake manifold gasket. 1 ac delco o2 sensor. I have not replaced the maf sensor but it was cleaned. I had bought a new map sensor but truck wouldn’t even start with the new sensor so I put the old one back in lmao. Also stock air box and filter replaced maybe 6 months ago

 

[2009TahoeLT]

Ok replaced all the injectors and the lean code is gone. Still have the misfires sadly. Seems to only misfire on cylinders 5, 7 and sometimes 8. Any other ideas?

 

[rdezs]

At this point I think I would replace the crankshaft and the camshaft position sensors, with genuine GM. Then do the relearn procedure. Particularly if it runs smooth at idle with no misfires, and still only misfires at RPM.

 

[dkad260]

Just recently replaced those with ac delco iridium I think

I would pull a plug and check. At least pull the plug on the misfire cylinder to check for any possible fouling.

Do you have a new coil on cyl 5 & 7? If so, check the wire to make sure it's fully seated. If not, maybe try swapping a new coil to 5 &7 to see if anything changes...or vice versa

 

[TonyTahoe2017]

I'm Following this thread. I have a pretty rough idle on my 2017 tahoe. It's bad at start up typically. I let it warm up and it gets better mostly. Stopping, accelerating, it can lurch or chug-a-lug. Cruising it mostly fine. I have coolant/oil in my cylinder heads. I've replaced all spark plugs and ignition wires and still having issues my self. I posted a different thread about it. Not sure how to link it. But here are my Shop codes: |Codes: -P0300 - Misfire detected. -P050D - Rough Idle. Cleared codes, monitored misfires through a scan tool, under load cylinders 1, 3, 4, 5, 6 were intermittently misfiring. Injectors and coil packs work good with no misfires. Checked spark plugs, porcelain look good. Recommend replacing all spark plug wires, as many of the wires have internal corrosion. After replacing the wires, the issue didn't go away. Noted that this vehicle has been in for this issue back in April, I looked up TSB's and there's a TSB for these exact codes (P0300 & P050D) saying the liners in the heads give out and leak coolant into the cylinders. Block test passed, but on a warm engine. Need to block test again after the engine fully cools down. Pulled out several spark plugs, put a bore scope into the cylinders and 3/3 cylinders that I've checked are all wet on the inside and the cylinder walls are glazey. Need to pressurize the cooling system and see if there's a leak once the engine is cool. Preferably need to leave the car over night. After pressurizing the cooling system over night, PSI dropped. Checked the cylinders in the morning, noticed valve stems leaking and coolant present in the cylinders. Recommend replacing cylinder heads, head gaskets and valve stem seals.|REPLACE - Ignition Wires