This is additional to a previous post... basically had to go down a 15 mile long mud and rocky logging road.

I washed the engine out and the car seems okay except now when I turn the AC on (idle or driving) the engine gets very loud, very loud and the idle goes up a but. I also feel like I have the brakes on a little bit when I'm going. When AC off is fine, but the idle is very very slightly surging here and there.

As soon as I turn AC on the engine roars and the idle goes up just a little.

Without AC it seems normal. No surging but the idle like I said is just a tiny bit rough.

That nightmare of a road certainly did something and the engine including the rad fans were caked in rocks and dirt. Took me a couple days to clean it out. Could it be the IAC or throttle body?

 

I am not a mechanic but my guess would be your compressor might be binding since it only happens with the AC on. It would be best for people on here if you provided the year, engine and any relevant maintenance history. Also what kind of sound do you hear when you say its loud? Is it a belt noise, squealing, grinding sound, fan noise, etc. My car also surges at idle slightly when the AC kicks on I think that is normal. See what info you get on here from senior members... good luck

 

It's a 2001 Monte Carlo SS V6 3.8L

Thanks the sound is like... possibly fans I guess. Like more of a 'roaring', like when you're in a plane and the engine roars before take off... not so dramatically but on a lesser scale. Then the whole car vibrates and all I hear is vibration during this time. The AC works during this period. I understand the AC takes a lot of power and people experience surging but this is well beyond surging. Turning the AC on is like activating the 'roar/vibrate' switch. Sometimes not immediately but pretty shortly after.

Without AC and using heat/regular air (or none) it is fine. However the idle is surging just very slightly. I don't even notice it on the RPMs. Just feels like rhythmatic, 1 second 2 second 3 second SURGE. 1 second 2 second 3 second SURGE. (repeat, but again nothing nearly as dramatic as the AC being on).

I'd take it in for a checkup obviously but I like to learn new things and not in a great financial place right now either. The more I can do myself the better. The car runs fine and everything otherwise. No CELs, etc. Pretty sure that logging road really screwed something up. As I said, the engine bay was full of not just mud but big rocks and stuff too.

 

Thanks for posting clarifying info for your problem... I did not own this engine or year I am hoping someone else will give you some info/advice soon... It sounds like the fans kick on when the AC does especially if its hot out and especially at idle. If the rocks or dirt you mentioned damaged the fan(s) or cooling fins on your radiator then they won't work well. If there was a problem with one or both fans every time they kick on you will have this problem. I would examine your radiator and fans with the car off for damage. Look for damage to the cooling fins on the radiator and see if anything is obstructing the fans. The surge could be many things but I would scan it. Even if there is no MIL/CEL now it could have a stored code. You can go to an auto parts store and they should scan it for free. I Hope this helps and you get a second opinion soon!

 

I would guess it the cooling fans as you say it happens when you turn the AC on. A easy check would be to disconnect the plugs on the fans and start the engine and turn on the AC and see if the noise is still happening, You can also isolate which fan is bad . Good luck