88MustangGX

so on start up (cold) the rpm's fluxuate from 500-1500 and repeats itself untill its warmed up. Is this normal? thanks!
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Pearlkobra12

no its not normal

945LSTANG

it should start at about 1200 rpm and slowly drop down to around 700 rpm. check your iac.

CantStopTheFox...

Welcome to my world I have the same problem....

I have tried a bunch of fixes from this article.....still broke

http://www.muscularmustangs.com/iac.php

My next step is the O2 sensors....I just replaced the X-Pipe and they tend to leave a lot of residue from the factory welding....besides the fact they are 14 years old

Hopefully that will help something....

Another place to look is a vacuum leak, and you know, I thought about it.......but would a vacuum leak just go away when the car is warm??

justakid

when i start mine, it idles at about 1000 rpm but drops to maybe 700-800.

idk if its normal but i plan on cleaning out my iac as well.

945LSTANG

thats normal