miss fire problems

[russmargo]

hi everyone
i have a 1996 993 that has a random miss fire code p0300 and sometimes i'll get all cylinders and more then less.
i had to do a top end because of sai and ever since then i got miss fire fault
i found away around the check station and was able to get there before a Cel
but not this year and had to get a waiver
i do get a ruff idle when engine warms up (about 5 to 8 min) when cold tach says 900 to 1000 rpm and runs very smooth but when it warms 450 to 500 rpms and some what ruff but the check station report says car idle was 800 to 850 rpm this is odd
my shop did complete tune and new wires plugs dist cap and belts they even changed the fan belt to a porsche oem and idle control valve
anyone have a clue?

[myfisch]

Check voltage

[Nine9six]

Apparently, your shop has no clue, otherwise they would have diagnosed the problem and fixed it, instead of throwing a bunch of new parts at the issue.

Without looking at the car, I can guess as well as your shop, without spending a penny.

How about crank position sensor out of spec, or potentially failing dual mass flywheel, (DMF).

You could also introduce miss fire, to mr extinguisher and see if that doesn't help.