engine drops to idle when letting off the gas at speed
1988 SE - 3.8, 99,000 miles
When engine warms up some, RPMs will drop to idle speed even at 60+ mph. Engine feels extremely rough, and just barely keeps from dying. No Fault Codes are generated, and this does not happen all the time. No stumbling on takeoff - the car pulls from a stop as though it were new.
Plugs & wires were changed last year, and the EGR (?) valve was replaced 9 months ago. I maintain the car very well.
Might be a dirty IAC?? I am confused since no Codes are being thrown. Any ideas?