Having some issues with idle on my s4. Had all emissions parts removed and ran into a bunch of problems so I put some of the parts back on such as cold start valve,BAC, ACV, and air pump. Car turns on fine but at start up idle jump to 3k for a bit then drops to 1500. I tried to adjust idle from the idle screw on the throttle body but once idle goes lower than 1500 it steadily jumps from 1500 to 1800 even when car is warm. How can I fix my idle issue? TPS sensor?

 

It's normal to go from 3000 to 1500 rpm right after starting. The idle should eventually drop to 750 in a slow manner if the car is in neutral. After the car has been fully warmed (20 to 30 minute drive time) then adjust the voltage on the Green/Red wire of the TPS w/key to on until it reads 1 volt DC. Also, make sure the timing is correct and the thermowax fast idle mechanism is working properly. If you can press upwards on the front throttle linkage after the car has warmed and it lowers the idle then this is a telling sign that the mechanism is not working properly or the throttle plates are sticking or the throttle cable is incorrectly set or the timing is off etc.

 

Starting the car in gear or not still goes to 3k first then drops to 1500. Even when car is fully warmed up still idles at 1500. I've managed to adjust the idle screw so that is doesn't idle jump between 1500 to 1800 and stay at a steady 1500 but if I adjust to go lower than 1500 idle will jump again between the 1500 and 1800 mark. No thermowax, dashpot, sec throttle plates, or egr. I will try to adjust voltage on TPS sensor though.

 

Had the same issue with my s4 check the clearance between the primary throttle plate and the throttle bore i forget the spec. Theres a small stop on the throttle body that needs to be adjust to fix the clearance.