wadeblues

I just bought this Paseo. The idle fluctuates when cold between 1200-2000 rpms. Once the car is warm, it seems to quiet down, but still idles between 1000 - 1200 rpms. It will also lurch when at a stoplight - more pronounced when the a/c is on, but still when not on. When cold, the idle sounds like it is gasping for air. It is a regular pattern (up, down, up, down, up, down). There is a (fakey) K+N air filter and enlarged exhaust, but I don't know if any other engine modifications were done. It is not a cold air intake, just a larger tube basically. Could this be causing the problem, the air intake or the exhaust, or both? If not, I have read maybe the battery connections, fuel filter, air intake leak, or vacuum problem. No problem on the first two, but I don't know how to check the latter two problems. Oh, also the brakes seem to be not grabbing well, and they were just serviced. Does this indicate a vacuum problem on this car? Can anyone help? Thanks, Wade