I just replaced my timing belt, for one because it has been 100,000 miles since the last replacement, and two there was a groaning noise coming from the belt area at startup that would last a good minute after start. So I replaced the belt, mechanical tensioner, idler pulley, water pump serpentine belt tensioner pulley, and the serpentine idler pulley. I go to start it up, and not only is the groaning still there, but now it acts like it wants to stall when I let up the gas at low speed. If it's just sitting there at idle it runs ok, but doesn't exactly idle smoothly. I thought I had everything lined up properly, but would the timing being off a hair cause this? Or could it be because the car hasn't been run in almost a month? And what about the groaning at startup?? I didn't replace the serpentine belt, because it looked brand new, but maybe it's what's causing the noise.

 

My advice on the groaning is remove the serpentine belt and start it back up. If it's quiet, then you have several options to investigate, and no easy way to isolate them, but very little concern of collateral damage if you just run to failure whatever is noisy.

Does your car have variable valve timing?

The bad idling is hard to say. If you're sure it's timed correctly, then maybe it just needs a little relearn time. Would be interesting to know whether the idle improves when it's not groaning. I assume they're not related.

 

What year model is the car? Do you have any codes?