"S.L." wrote: '98 Malibu LS 3.1
Bought at 46K, has 90K. No tuneup since purchase, always ran fine.
But now, in RAINY WEATHER ONLY:
1.) Starts good, runs good for a few minutes, then runs rough.
2.) After full warmup, smoothes out and runs good again.
Any recommendations where to start? Steve L.
It is probably high voltage breakdown.
1.) Moisture on ignition parts (Distr cap, plug wires, plug insulators)
provides easy path for firing current to go to nearby metal rather
than across spark plug gap.
2.) Widened plug gap in old plugs is harder for spark to jump.
3.) Old ignition parts have deteriorated insulating abilities.
4.) Richer mixture (easier to ignite) and higher idle speed when
first started permits relatively smooth running.
5.) After mixture becomes leaner and idle speed is lower,
6.) Full warmup dries moisture from ignition parts and improves
insulating ability and smoothness returns.
I think it's time for that tuneup.
Wendy & John.