Missfire when engine runs for a while.

[Whitey]

I have a 1uzfe which ran on Spitroniocs. I removed the spitronics and fitted original management.
Now the engine starts and runs smooth and normal for a while, when the engine has run for a while it starts misfiring and revs pick up a bit.
If I switch off the engine and start again, it runs normal for a few minutes and starts misfiring again.
Where do I start fault finding?

 

[gloverman]

With the basics. Plugs, leads, afm checked etc. Then check ecu inside and wiring. This test is helpful.