Engine misfire when warm

I have an issue with my 85 928 S... She starts, idles and runs great till I get some heat in the motor. It then beings to miss and backfire with rpm's on 2000.
This only occurs one I have been drive for about 15 minutes or so.
Even hot, the car idles fine but cant rev above 2000 rpm’s or so without shaking, cutting out and backfire.
I have replaced the battery, did a visual inspection of engine bay, checked spark plug wires in dark for aching, found nothing. I feel it may be a intake manifold issue but not sure how to diagnose that.
Any suggestions or feedback work be greatly appreciated.

It could be a vacuum leak, which is common.

Perhaps look through these tips, in particular the vacuum leak ones near the bottom: nichols.nu/cat03.htm

Also, it could be something simple like bad gas.
Are the cap, rotor & plugs recent?
How about the ignition wires?

I am not convinced that it is a lean mixture (Intake leak)

When a module or even a coil gets hot it can start to fail.

I coil will miss fire or just quit.
A module will do the above and anything else it feels like doing, including firing at the wrong time.
I do not have a lot of experience with 928 computers and you need a scan tool or scope to see what is happening.

Do you know anyone in your area with a sharktuner or a scope?

Brad

Thanks for the reply.

I will review the document and check vacuum lines.
Fuel was recent... Yes, newer cap, rotor, plugs and wires... maybe (2yrs) with under 300 miles since replaced. And again, only happens with warmed to normal operation temperatures.

thanks again

See if you can find anyone close to your area on here

forums.928oc.org/vbulletin/forumdisplay.php?f=15

There is a part called a temp II sensor on the intake, perhaps it has malfunctioned.... www.electronikrepair.com/page9.html