Recently when driving the car for the first few minutes there will be this metallic grinding sound, like someone drilling into sheet metal, when accelerating. The car will seem sluggish and the engine sounds like it'* under more stress than it should be. If I give it a lot of gas, all the sudden it clears and there is a surge of power and the engine sounds like it should again. This is a recently rebuilt series 1 supercharged and is running great otherwise. My initial thought is that it'* the supercharger in some way (It is NOT the coupler, I have replaced that recently). Keep in mind, in another thread, I describe how all the coating on my supercharger seems to be flaking off. Could this be related, maybe sc bearings?? Any other thoughts?

Is this when you first start it cold? That'* the IAC. Normal.

It does seem to go away when the engine gets warm, same with the grinding sound. But this kind of thing has never happened before until recently. And I can definitely hear a sudden change in how the engine sounds, and then a surge of power when I give it more gas (obviously), but only after a pause, like something had to clear for the engine to get back in sync, it'* weird.

It'* kind of like a choke. Once the engine warms up a bit it closes off. Have you made any changes to the air filter? Changing from the stock air box will make it more noticeable.

It'* got a stock air filter, replaced just a little while ago. Any thoughts on the grinding sound?

An open or larger air intake will make that sound. Check everything from the throttle body to the air filter; make sure there are no cracks, holes, loose screws or whatnot. Not sure how to test an IAC, but swap it if you can't find anything else.

I had a similar 'grinding' noise problem that we all thought was coming from the engine, it sounded terrible and was really amplified when driving along walls or parked cars. It was actually the catalytic converter, the internals were all busted up so i replaced it with a straight pipe and now it'* nice and quiet again, maybe give that a shake, if you hear anything rattle in there i'd say give that a try.

Come to think of it, the exhaust has sounded a little odd lately. For a second when accelerating I sometimes hear this loud rumbling sound and the exhaust rattles when I first start the car. I'll check it out. But when you say you put straight pipes in, does that mean you took out the cat, and isn't that illegal?

Update: I got under the car and wiggled a few things around and nothing seemed to be loose or rattle. The muffler is a bit rusty but anything before that is fine. Here'* an example of bad timing, my tags are up and I have to go to the DEQ tomorrow, so I'll know for sure then if the cat isn't working properly. I don't have check engine light on so it'* probably fine.

Okay, now I think I know what it is. On the freeway today I tried to get up to speed quickly and the car would loose power when the boost got past 0psi. The gauge said I had boost well past 0, but I know I wasn't getting any of it. It did some more tests and I feel good pull until I give the car enough gas for the boost to go past 0, then it'* just plain slow. I've been reading it'* boost control actuator or boost control solenoid. Does this makes sense for the quote above? Maybe the actuator is sticky and that'* why it would clear sometimes and I'd get power (it also seems to be happening when the engine is warm now, not just cold). Also is anyone familiar with this problem on series 1 supercharged engines?

Check to make sure it moves freely. Also watch to see if it moves when you give it gas.