I solved an almost identical problem on my 300TE by replacing the air flow meter potentiometer, though this was after 265000 miles.
The problem has been well documented on the site recently. A search should reveal a few threads.
May not be your problem but worth checking out.
90 300TE 24v (M104 eng) 207K miles
87 300TE (M103 eng) 269K miles (and never had the head off!)
86 300TE (M103 eng) 230K+ miles (donor car)
95 Toyota Lucida diesel 4wd
86 200T 165K miles (sold)