I can not think of anything plausible that would make it misfire when the SAI pump runs.
Wild guess
Somehow the secondary air plumbing is backwards.
There is an electrical issue when the pump runs sending voltage or taking Voltage away from the coil pack
When the secondary air kicks on it is causing the stainless pipe running across the firewall to vibrate on the coil packs giving you a misfire

 

unplug the sai power harness and see if the missfire codes go away

 

I get the same thing but I also get SAI codes also. Have you gotten anywhere on this?

 

What are all of your exact fault codes, don't worry about the other problem, lets work on how to fix yours.

 

Mike,
I have a 2002 disco with approx 125k miles. Last week my oil pan gasket apparently blew on highway and shortly after CEL started flashing throwing misfires in cyls 5&7. The shop I towed it to replaced oil pan gasket no problem (apparently one corner of gasket wasn’t put in flush prior). As for the misfires they cleaned out all cylinders and checked compression, all good, then replaced all plugs, still misfiring. Next replaced wires and coil packs as well as new manifold gasket (which had rtv sealant in place with no gasket?) and still misfiring only in cyl 5 now. P0305 code.

What could possibly be causing this misfire? And what do u recommend trying next? My mechanic noticed that the secondary air injection system isn’t even working at all. Pump doesn’t come on at ignition at all and believes this could have something to do with misfire? Your advice would be much appreciated!