Im asking this on behalf of a freind. My freind just has and 98' Lude' with a $h!t load of mods on it. the weekend he had a Throttle body spacer and UR underdrive pulleys put on. after those 2 mods it now idles really rough its like it gose from 1000rpm to 1700rpm constanly now. I think that the ECU wasnt unplugged during the installation of them, i just wanted some feed back on what it could be.

 

Did they bypass the coolant lines that run through the throttle body. Usually people do that in an attempt to keep the hot coolant from heating up the throttle body. But it makes it idle like shit when it's cold out. Either that or the TB spacer didn't seal up good and you have a vaccum leak

 

Well we took it out last night and it was around 30, and it was idling like shit. that could be the problem or the Vaccum leak like you said. Thanks for your help