94 Buick LeSabre EGR Problem

Hi,
1994 Buick LeSabre 3800 engine 148,000 miles
Engine misfires/chuggles at part throttle and light load (about 60 mph). Has good acceleration/performance otherwise.
P1406 History code. Scan tool shows EGR Actual % swings wildly when the chuggle happens but the EGR Desired is steady.. Engine runs great when EGR is unplugged. Tried a new EGR valve and it didn't fix the problem. Intake manifold vacuum is high and steady when EGR is disconnected. I could use some suggestions!!!!
Thanks,
Ron
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Probably a pcm....Bobo

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What's a pcm?

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the pcm is the Powertrain Control Module.. I had one about 2 months ago doing the same thing.. the pcm would activate and pulse the egr valve even though there was no request...Went totally nuts... If you want more info, post and I can give you pinouts, and voltage checks when I get back to work monday...

mph).
but
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Did you clean the carbon out of the ports?

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Could be something like a bad EGR pintle position sensor (part of the valve). Is the actual value staying pretty close to the desired when it's running OK?
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Robert Hancock Saskatoon, SK, Canada
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Hi,
Thanks for the suggestions guys! I hope it's not the PCM but not hard to replace if it is. I didn't see any carbon in the ports so that isn't the problem. Robert, the actual value stays close to desired until the engine starts to run rough then it swings wildly. I replaced the EGR with a new GM valve and it did the same thing. Again, the engine runs really good with the EGR valve unplugged.
Thanks.
Ron

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