My 89/240 does the same thing I have gone down the list to solve this problem.I have a 951 ECU and I'm starting to look to put another computer in the car.When some one find this problem let know.It will stumble for the first 10 seconds and the check engine light will come on but no code.The car doesn't do this every time thats where it's hard to solve.Fuel pressure is right in line for holding over night,so that rules that out.
Rodney

Well there are many areas to check initially for the poor running.

I assume you have pulled the plugs to see if there are clean. If caked with soot, that might indicate either the injectors are clogged or wires are bad.

I am helping a buddy with an 85 240 that runs about like what you are describing - and upon pulling the connector off of each injector, it was found that two of them were not working properly.

Of course, it did not hurt that I had a tech with me that used a test light to determine that each injector was getting proper power.
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' Of all bad men religious bad men are the worst. '' (C S Lewis ; on Evil Men) 89 764 (158K), '94 940T (240K), 85 245 (219K)

I forgot to add, the car is an 89 240.