Perhaps your electronics are off kilter.Clean your ground points.
The areas to look at are;

1. On positive battery connector there are usually 2 wires coming out
of it. one is the thick regular one and the other is goes through the
fusebox next to the battery. Clean that connection. I had a problem in
my sentra that got so bad that the car would stall. It turned out to
be that the positive connection to the fuses was corroded beyond
belief. Cleaning that restored the car to normal.
2. Alternator connection. Unplug and re-plug the connectors after
cleaning them with a steel toothbrush or some such item.
3. The negative battery cable usually connects to the transmission
bell housing. unplug and clean that.

Hope this helps.

CD

i would not expect this, unless #4 has excessive blowby or something
has
happened to a valve or valve guide or valve guide seal.

definitely, a compression test of all cylinders would tell you the
health of each.

Thanks for the response.

I didn't know about the electrical connection thing so I will check it out.

The way #4 behaves (i.e. no loss of idle speed when the spark plug wire is
removed) was the same before and then after all the items were replaced.  I
noticed the probelm with #4 and after changing rotor, sap, all spark plugs
and spark plug wires the result is the same.

The spark plug wires were Bosch 09814 Wire Set (Stainless steel Mag winding,
100% pure Silicone jacket, Kevlar reinforced core. Lifetime warranty.  I
first started using them on this vehicle April 2001 when the car had 150K
miles.  I replaced the Bosch set with the exact same part number in March
2006 at 250K miles because wire #1 developed a small hole in the insulation.
It was that set which was on the car Monday.  Tuesday I replaced it with a
third set of the same part number (no charge replacement) thinking perhaps
there were breaks in the wire.

The spark plugs removed were Bosch Platinum FR8DPX.  These plugs were
installed July 2007 and had only 5,000 miles on them (all local town
driving).  They looked good but since it seemed like an ignition problem at
first I figured it was worth replacing them.  The set I installed Tuesday
was the NGK BKR5ES-11.  They are copper cored plugs.  I think they are very
close to OEM plugs.

The gaps was checked and all were at 0.044" as they were installed.

I of course kept the Bosch plugs since they had little miles on them.  #1,
#2 and #3 look almost identical with carbon buildup.  Just a little though.
#4 seems to actualy have less carbon buildup.  If needed I could post a
photo I suppose.

Mark