This only happens when she's been sitting the whole day, when the engine is cold, pretty much first thing every morning.

I get a rumbling idle, and then it smoothes out, rumbling again, smooth again etc.. The rpm needle is not going crazy or anything. It's up around 1500-1800 rpms on startup, then as it gets down to about 1000 below, she is smooth and quite. You cant even tell the engine is on.

Can someone point me in the right direction on what to look at, as to what's causing the idle issue on start up?

 

My 92 SC3 does the same thing exactly. It's live vibration for about a second or 2 then no vibration for a second or 2 and only at cold start and only while it is idling above 1200. I was thinking harmonic balancer but I don't know for sure.

 

bump...thanks

 

on startup the car looks at the engine coolant temp sensor to find the right a/f ratio. once warmed up it then relys off the o2 sensors..