It's difficult to diagnose a sound one can't hear but here goes.
A possible cause of "chugging" and a higher idle that comes to mind is
injection timing. That includes the timing chain, camshaft timing vs.
the crankshaft (crank should be no more than 5 degrees ahead of the cam)
and the start of fuel injection delivery. I'd check the cam before the
That said, you should know that the estimated useful life of these
diesels, IMHO, is 250K to 300K miles. Unless your engine has had
extraordinary maintenance, yours is at the threshold. The definitive
test is a compression check which I'd suggest you have done before the
winter for if the compression is falling you should know that the car
will be marginal when the cold weather arrives.
You obviously like and care for this 24 year old car. If the compression
test is bad news perhaps the car can be your "summer car" for there's no
economic sense to rebuilding this non-turbo engine. Or, perhaps a used
turbo diesel engine and transmission could be installed. That would
solve the impending problem, if that's the case, and repower the car
with an engine of nearly twice the power for less cost than an overhaul.