When placed in drive the rpm's dip on 2000 Lincoln LS

125K miles. just had tune up replaced spark plugs etc. Lately been noticing a hesitation when shifting to Drive.
Now after starting and placing into drive the rpm's dip low and today it dip so low the engine conched out.
I got it started again but in both Reverse and in Drive the rpms dip low. What could be causing this? (engine light did not come on)

Asked by for the 2000 Lincoln LS
I would look at the idle air control valve first, and see if it may be limiting air flow to "choke" the engine at times. This or some throttle body issue could be causing the low idle also.
answer#2 was right on....Thanks,
1 more answer
take compression on all the cylinder, might have a bad cylinders.