I suspect a vacuum leak is occurring here, and I was hoping the NAM community might be able to help me on where to look.

Ever since I replaced my SC pulley with a 15% WMW pulley, along with new upper and lower motor mounts on the passenger side of my 2003 MCS, I have been getting some MASSIVE vibrations on cold idle that get worse during acceleration from a stop and at low RPMs (1000-2000). The car also feels like it has a cold - it no longer accelerates smoothly and I feel like this is not just normal added NVH from the new mounts. I feel like there's a vacuum leak somewhere and I think it may have to do with something occurring when I jacked up the motor for the installs.

Does anyone have any idea what vacuum leaks are common to a 2003 MCS that I should look for?

I took a couple of videos. The first is just a cold start, sitting at the entrance to my work waiting to leave. You can hear the vibrations (which would be worse if it not for some duct tape jammed between the dash and the windshield) just sitting at idle, and then you can hear how bad it sounds under acceleration, especially at low RPM. I can't really put how it feels on a video, you're just going to have to trust me on the sluggishness. It's not right. Power is leaking somewhere.

It's 6 1/2 minutes - you don't have to watch it all to see what I am getting at. It's also not visually appealing. It's just about the sounds.

http://www.youtube.com/watch?NR=1&fe...&v=Zb0-phgU6b0

The next video is after my 25 mile commute this morning. Just a 15 second clip of the idle after the car is warm. Quiet as a mouse. But still as sluggish under acceleration from a stop and low RPMs. Believe it or not, yes - the car is on and it is the same camera I used to record the other video!

http://www.youtube.com/watch?v=ZVZQ1...NwDU0nnirNOWc=

Anyone have any ideas of where to look?

Here's what I have done so far:

I pulled the IC boots to make sure they weren't leaking. They weren't. I checked the quick connect vacuum hoses on the passenger side that I had to disconnect for the tensioner tool to have room and I am sure they are firmly planted. I rechecked and retorqued all the bolts associated with the new mounts. I disconnected the ground strap and sanded off all the corrosion to get a better connection. I have reset the computer. The air filter is a K&N drop in and is clean. I checked both the MAP and TMAP sensors - the MAP sensor was perfect, the TMAP sensor has some oil residue but cleaning it made no change...

I'm going to pull apart the throttle body and bypass valve tomorrow on my day off to make sure nothing's leaking or dirty in there (the bypass valve is a new DT valve just installed last year)...

Your help and input is appreciated!

 

if they are aftermarket motor mounts that vibration seems normal. As far as the hesitation have you checked to see if your belt is slipping? Did you use the correct one when you changed pulleys?

 

I ordered the kit from Way Motorworks. He supplied the correct belt. As far as I can tell there is no slippage.

If the vibration is normal, why does it go away after the car warms up? I mean even after the car warms up, the vibration is more than what it used to be, but it's not so bad that the whole dash sounds like it wants to break apart.

The hesitation is baffling though. Maybe it's an O2 sensor (or both) but it would be one heckuva coincidence. I am not throwing any codes on my code reader, but that doesn't necessarily mean anything.

I may try putting the OEM mount back in and give it another try. If it is just the new mount (though I am telling you I don't believe it) I will sell the TSW and get something else. The BSH lower mount is staying.