Idle problem & Coolant smell

I have a 2000 GMC Sierra, 2WD, 4.8L. About two months ago I had no heat, so I changed the thermostat, and nothing. So then I did a flush and fill, and bought the flush and fill kit from the store and followed the directions. That took care of it. After that I had heat. Now I can still smell a little faint smell of antifreeze. I washed the motor off, and everywhere that antifreeze could of sat, and created a smell. I'm not losing any coolant, tank never moves off cold mark. Also checked the water pump, intake gaskets, and head gaskets visually, to see if I could see any leaks, and nothing. Also after doing the flush and fill, I noticed a change in the way the truck idle. It now has a slight miss or hesitation at idle. To try to correct the idle problem, I cleaned the throttle body, iac, air cleaner because I have a cold air intake, changed the pcv valve, also ran some premium gas with some seafoam in it. It got a little better, but it still has a little miss. Any help would be great, and thank you in advance.

Do a full scan and look for any misfire counts or the engine running lean or rich. Double check for vacuum leaks also. Look at fuel trim readings on the scanner. Pressure test the cooling system.

what kind of cold air intake do you have? alot of the cold air intakes (especially K&N) will ruin a mass airflow sensor. The oil from the aftermarket filter contaminates the sensor and gives false readings. sometimes it will throw DTCs and cause a MIL for P0171 (Bank 1 Too Lean) and P0174 (Bank 2 Too Lean), while other times it wont cause a MIL or DTC. That could be part of the driveablilty problem. As far as the coolant smell, can you smell it more noticeable in one area over another? Inside the car? Engine? Exhaust?

you may also have air in the cooling system from when you did the flush. to check, remove the radiator cap (or reservoir cap if radiator cap is not accessible) and start the engine and turn the heat on high and let the engine idle for a few minutes. if there is any air in the system, you will see bubbles coming out of the reservoir or radiator.

On my 2000 Yukon with 5.3, I find that the throttle body need to be cleaned by hand every 10 - 15K or I start to get a rough idle. I usually just clean ist every oil change now.

How does the throttle body look on the inside?

//2000CAYukon

I don't have a K&N cold air intake system. Its just a washable filter. I also clean the the throttle body and IAC often. At least three times a year. I ran a tech 2 on my truck, and every cylinder except 1 and 8 had a misfire. Putting all the misfires together with the antifreeze smell tells me the junk dexcool is wearing away the intake manifold gasket. The coolant is leaking internal. Number three cylinder was the worst with the misfires. I'm going to drain the coolant again and change to green or yellow. But before I do that I'm going to change the intake manifold gasket. Do you guys recommend the plastic gasket or the metal? The guy who ran the tech 2 on my truck finding the problem said it didn't matter as long as I didn't use dexcool again. The leak internal also is causing my bank 1 sensor 2 oxygen sensor to not function properly, so I'm also going to have to change that as well. Any other thoughts or suggestions are appreciated. Thanks to everyone on here, always a big help.

Definitely go with metal reinforced gaskets. They are obviously less prone to wear and they hold in place much better. as far as the washable filter, what brand is it? glad you got it figured out. be sure to get all the dexcool out if your going to switch. mixing it, even in the smallest amounts, is not recommended. Hope this helps!

I couldn't tell you what brand the air filter is. I bought the whole cold air intake kit on ebay, for about a quarter of the cost of a k&n. Turned out to be a nice kit though, came with a heat shield, a nice black painted 4" aluminum pipe and everything else. Thanks again

ok if you bought the whole kit, you should be in good shape. i was just making sure you didnt buy just the filter bc like i was saying, it will ruin the mass air flow sensor, but if you got the kit, its good to go. and if your going to change one oxygen sensor, might as well change them all if you got the money bc if one is contaminated from coolant in the exhaust, odds are they all are.

Ya, I probably will change them all over time, but there so expensive. Ya I always was a little leary about the k&n air filter, because of the air filter oil. The funny thing about my coolant smell is you can't always smell it just sometimes, and it looks like I just have lost very little coolant since this whole thing started. My buddy who ran the tech 2 on it says that was probably because the gasket just started to leak.

Is there any other way to check to make sure the intake gasket is leaking. I mean I definitely trust my buddy that did the scan on my truck, but I just want to be 100% sure. Thanks

well if its leaking externally, you can have the cooling system pressure tested to see if its leaking at the intake or sometimes if its bad enough, you can see where fluid has been bc it will have dark residue spots. Also, you can check the oil. If the intake gasket is leaking internally, you will have coolant in the oil and it will appear to look kinda milky, depending on how bad it is.

The oil doesn't look milky at all, but we are sure thats its leaking internally and my truck is burning it. I think it just started leaking not too long after I did the coolant flush. Its not leaking externally because I checked everywhere it could be leaking externally and no wet spots on the motor anywhere, and no leaks on the ground. I once had a guy tell me you can see if the intake is leaking by, pulling the pcv valve out of the valve cover, stick your finger in the hole, if it feels like it sucking, or has vacuum its leaking. Have you ever heard of that?

no I've never heard of that? I would think that considering the pcv valve has a vacuum hose running to it, that if you felt vacuum, it would be normal?

Changed the intake gasket today, and re-flushed antifreeze to run yellow coolant. After changing intake gasket we flushed the system, re-filled and ran it for awhile. Ran it on the tech 2 again, no codes were found, and no misfire counts. Runs great, and no hesitations or misses.

sounds great! glad you got it running good again!