3800 OBD1 codes issue w/ EGR

hello all- i have a problem i haven't been able to diagnose. i've got a '94 Lesabre with the L series 3800 that keeps setting an OBD1 code of 401 "Delta RPM linear egr flow failure" code i read off with the Diacom
software.
i have replaced the EGR valve twice, the last time switching with another 3800 engine's new EGR valve that doesn't set codes. the valve is good.
the code will set after about 150 miles of continuous driving, then the idle will be rough until i disconnect the egr valve, then the idle smooths. the code is not set with short trip driving-- just a long continous one.
when i clear the code, it will remain off until another long jaunt.
no other codes are ever set. new plug wires, coils, ECM connector cleaned with DeOxit and manually re-inserted several times. EGR passages are clear. i'm puzzled.
so. i am assuming the 'test' the ECM runs thru to check the operation of the EGR valve is some how telling the system the EGR is bad. does the ECM check for an RPM drop after activation of the EGR? what else could cause the 401 code to be set assuming the EGR valve itself is good?
any help appreciated! -dan Bemidji, MN
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This might not be at all related, but SOMETIMES problems with the quad driver module in the ECM that controls the EGR, can set false EGR related codes.
-- GW - note incorrect email address "It's good to yell at people and tell them you're from Tennessee. That way you'll be safe." - Gary Busey
Daniel Houg wrote:

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