Sudden low cold idle

[mark houghton]

So riddle me this. The other day I lit up the beast only to experience a super low 300 rpm idle from stone cold and took a couple cranks to keep running. Ordinarily she lights right up and settles into around 900-1000.
WTF I told myself, so hooked up the gauge and checked all the pressures...all within spec cold and hot as well as system pressure. Also did the fuel accumulator leakdown test over 20 minutes and held at about 3 bar...no issue there.
Disconnected the gauge and fired her up...and twice since then over the last several days...all is good as it should be.
The only thing I can figure - well two things - is either my AAR was stuck closed and not providing enough bypass air to support high cold idle, or one of of my fuel pumps decided to stop pumping then had a change of mind.
I hate it when I can't put a definitive finger on things.

[908/930]

I think you are on the right track with the AAR. Did it respond if you give it some throttle?

[mark houghton]

Originally Posted by 908/930

I think you are on the right track with the AAR. Did it respond if you give it some throttle?

Once the idle idle got steady she was fine and ran just fine down the road.
Today I pulled the pump relays and re-inserted each individually to check pumps. Both pumps are running and car started up and idled no problemo as it should. Then I put 60 miles on her for a late autumn spirited drive. Running like a...well...raped ape as they say, settling in at 950'ish idle rpms fully hot and bothered.
Funny though (I know these cars can run on just one pump), with the engine running and pulling the relay to the rear pump the rpms would drop just slightly as anticipated. Pulling the front pump relay a very minimal effect...but I could feel both relays in my fingers energizing when plugged back in. So as I said, both pumps are running but perhaps a dirty connection for one or a problematic relay.
Right now things are perfecto!