You can peak under the EGR location to see if the PO had wrapped the harness.
P306 could be any slew of causes but 180k is not too high of a mileage but parts or your 97 is 25 yrs old. I believe I had replaced 85% of parts in my 93 due to age. Only the engine and tranny mounts are original.
To...
Ok...
P306 is Cylinder 6 misfire:
-Could be the harness under the RGR is cooked
-Spark plug and spark plug wire to #6
And check Rotor cap
-Due a #6 injector check or service
-Last and not least due a leak test and compression test
If coolant is being consumed then it's an early indication if...
Definitely. Its a starting point to the issue. Most common is code P0401. EGR.....caused by carbon build up. Easy fix or $$ with OEM parts. You can bypass the P0401 with a 1ohm register hack to trick the ECU.
Huddexpo sells them $36 (EGR temp sensor plug)
Miles?
-Fuel filter could be clogged
-Fuel pump could be intermittent
-TPS sensor....(intermittently flashing check engine light for no apparent readon)
but w/out the code it's like throwing darts