My car (2002 R53, 80k miles, manual) overheated and I took it to the shop to have them fix it, only they were going to charge me 2800 because the EML light was coming on and they wanted to replace the wiring harness and the water pump. Since I paid 3900 for the car I wasn't going to do that so my dad and I pulled the car apart and did it ourselves. Only the water pump wasn't bad. We replace the thermostat while we were there and I went ahead and installed a 15 pulley and better airbox for more power. We put everything together and tried to start it and it ran like crap (surging, sputtering, like it was missing on a cylinder). So I replaced the plugs, wires, and coil pack (the leads were rusty) with an MSD set and the EML light stopped coming on and it ran smoother, only it still isn't roadworthy. The issue I am having is that when I turn on the car, the engine revs to 2k or so than settles down to 1k and surges to 1200, back to 1000, etc about every 2 second cycle. And it looks like I am leaking coolant from around the expansion tank. Any ideas on what the problem could be? I thought a vacuum leak, my dad didn't know, but I'm out of ideas.

 

Coolant tanks leak around the seam..common failure...about $40-60 to replace.
Any codes?
Eml comes on usually with a code to help you know where to start looking....

 

P.S.
When you reassembled everything...did you reuse the SC gaskets or get new ones?

 

We reused the seals. Please tell me I don't have to replace the seals.

 

Time to start over...
The green SC gasket is a onetime use part...it leaks when reused....matches your issues..