98 3.8L Periodic Shudder

[treetops2000]

Engine shudders/loses power/CEL flashing for about 30 seconds, then suddenly regains power/speed and CEL stops flashing. Happens 35mph - 60 mph. Also runs rough sometimes at slower speeds. Occasionally difficult to start. Problem has been getting worse over past few months. Scan: P0301/P0304 Cyl 1&4 misfire, P1537 IMR Ctrol - Bank one open.

Have read threads about P0301/P0304. Mechanic says the P1537 means replacing apparatus that supplies air to cylinders.

Could all this be caused by EGR ports dirty? Help before my CEL light burns out!