Symptoms of bad timing belt? (Wierd start/idle...) 4000SQ

[John <jb@access.digex.net>]

After going thru the archives, I am suspicious my recent problems
might be the timing belt.

These problems are all very recent - the car ran great up until a
week ago...  (Read the bottom for current very wierd symptom!)

My 85 4000SQ has problems restarting when hot (sometimes).  It will turn
over great, but if and when it decides to start, its RPMs start way
low and then pull up to normal in about 2 secs.

When cool, it starts right up, although half the time it issues a small
white (bluish?) cloud.  And a week ago it backfired once on startup.

I found the rotor worn and the cap contacts had white chalky stuff on
them, which came back after cleaning.  A new rotor and cap haven't
solved the problems.  The wires are fairly new, but not the plugs.

Now I notice my tach showing idle at 14-16 rather than the normal 9-10.
And WIERDEST OF ALL, when I'm coasting, the car seems to alternately
push forward, then slow repeatedly (a cycle every second or so)!
But when I give it gas, it's like normal - quite peppy.

Should I get the timing belt replaced?  Or am I off on this?

Thanks (for the billionth time),
John
'85 4000SQ