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Ok I have this really weird problem with my 92' Civic 1.5 auto. I'v e got a tc throttle body, Obx intake and a custom exaust. Im also running nitrous, but thats irrelevant. Where my problem begins is when I turn on the car the engine revs to 1.5 and then drops to 1 and keeps repeating that until it heats up. Then when it heats up, it idle's at 0.3 barely at all. It sometimes cuts off because of it. I've tried idleing up, both ways on the throttle body and it just won't idel up. I've replaced the O2 sensor and disconnected it altogather. The timing belt is also brand new. it's an annoying prob that I would like to fix. I'll give ya a cookie for some help.

vaccum leak, bad tps sensor, bad IACV, idle set too high. attempt to set the idle with the engine warmed up.

unplug the IACV on the intake manifold and set the idle with that disconnected. it will give you a check engine light while it's disconnected. either clear the memory code, or remember that it's there once you get the IACV plugged back in. my car was idling like that for a while. it was actually set to idle too high. also check your coolant level and your coolant temp sensor. the ecm looks at coolant temp when it determines idle speed. if your coolant is low or the sensor is bad, the ecu will get pretty confused and do strange things to your idle.

check the pcv valve make shure that the hose going to the intake man.. is plugged in.