Rough cold start
This started after filling my 77 280z with unethonal gas for the first time, 87 octane.
Normally I put 91 regular.
Dont know if related but need to specify.
Since then, first crank of the morning is difficult.
When I turn the key to start, the engine turns almost immediately matched with idle of 2 to 300 rpm, then stalls.
I do this 3 or 4 times, then idle catches up to around 5 to 600 rpm, then when temp starts getting up (after approximately 15 to 30 seconds), it idles perfectly at around 9 to 1k rpm.
After engine warms up past 120 degrees, I can turn the engine off and it will start like a dream, a few cranks of the starter and then turns over
Went to dinner last night, same starting issue when I left the restaurant, after about 2 hours of engine sitting, but only needed 1 or 2 turns of the key to start rough idle
Moved to Colorado, wondering if altitude would play a factor, or what's going on?
Thanks for the help