rough idle on cold starts

[RED95SHO]

Did a search with no comments on a rough idle on cold starts which goes normal after a minute driving without hesitation. The idle is at normal rpm but rough. On warm start ups, no problem. After my commute, 86 mi round trip highway,the next cold start is normal. It happens when I do some city driving or have to move the car and shut off before it warms up. The next cold start will be rough. No codes and the cylinder balance test was a 9. The IAB is a new Motorcraft part and that fixed a cold start no idle, stall problem with a 124 code. This summer I changed plugs, wires and seals when oil was in the wells. No oil in there now. Motorcraft plugs and Delco wires. Any ideas on why only cold starts and why just for a moment?

 

[GBpacker_Sho]

I believe its common in all SHO's. I know mine does it. If it is really horrible you might want to replace the throttle positioning sensor. I wouldnt worry bout it, to much

 

[fricker66]

My 89 has done that since new. While I'm no believer in the general use of the higher octane/higher priced fuels, I have found a solution for the cold start stumbling. With a tank of 93 octane, the engine no longer shows any signs of stumbling. If I fill up next time with 87, it's back to stumbling and hesitation on cold starts. Not a true scientific study but it's been consistent with the grade of fuels. Might see if that helps your situation. For me, the extra $3-4 a tank for premium is worth the ability to immediately take off without fears of stalling or lugging the engine. As always, YMMV.

 

[RED95SHO]

The things I learn on this site! Thanks, will try the higher octane.