Why does my 87 na idle bounce when warming up? it bounces consistently from 1000-1500 until it warms up. then it kicks off and idles normal. Also when driving it cold the tach reads about 500-1000 rpm off what the actual reading is. So say im doing 2000pm in 4th gear going 40mph the tach will read 2500 or 3000.

 

check tps

 

this happens to my car too.. but its not just when warming up it happens randomly.. well not random... only at night when my headlights are on. my travels from 1000-1500 as well

diagnosis anyone?

 

First thing to fix for surging idle is the TPS setting and correct idle speed. After that, start looking for the vacuum leak.