Odd engine problem on a rainy day . . chug, chug, chug, chug

[SJ]

It was cold, foggy, and raining yesterday. Temperature was about 50 F.
Oregon style weather.

Drove the 90 100Q to the store . .about 2 miles away. Parked and shut off
engine.

Came out of store in about 20 minutes, started engine.
Started up ok, but sounded like it was running on one cylinder. Pressing
down on gas pedal did not change the RPM . . .chug, chug, chug, chug . . . .
sounded like a one cylinder diesel engine on the African Queen.

I let it run this way for about 30 seconds or so . .figuring it was wet and
something in ignition was misfiring. Maybe it would dry out a bit.

After about 30 seconds or so, the problem cleared up, no more chugging, gas
pedal worked.
I drove home gingerly. There might have been a slight hesitation or stumble
going from idle to part throttle . . I'm not sure. I was very easy on the
throttle because I didnt want to be towed home.

Today, I sprayed the ignition wiring, coil, booster with WD 40. Weather is
sunny, dry, 35 F.
Car started up with no problem. No missing, no hesitation.

The ignition wires and cap and rotor are about 1 year old. Maybe 4k miles on
them. Same for the plugs.
ISV valve was cleaned about 500 miles ago . . nothing was wrong with it .
.just preventive maintenance.

Any ideas?


SJ
85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q