My poor Saab 900 is having touble getting going. I was away for about a month, and got the oil changed before I left. When I came back, I drove the car to my grandmother's and back, about 15 minutes each way, and it ran fine. The next day, it stalled right after starting.
When I try to start the car, it revs to about 1400rpm as usual, but drops slowly to 0 instead of settling at the standard 800rpm idle. On subsequent attempts, it stalls out much quicker. If I let the car sit overnight and try again, the rpms die a little slower on the first try.
The throttle body is clean and the butterfly valve doesn't stick. I looked for vacuum leaks but saw nothing obvious. (Not sure how to check thoroughly without a running engine.) The air filter is clean too, to be sure.
Idle air control
I cleaned and oiled the IAC valve. When I turn the assembly quickly in my hand, I can feel the rotor turning easily inside. That's not supposed to have a return spring, right? If not, it seems to rotate freely. Also, the voltage across the contacts jumps when I turn it, so I figure it's working according to Faraday's Law. It also shows a steady resistance across its contacts. One wire to the IAC is grounded and another is getting 12v.
Throttle position sensor
Same thing for the TPS. The resistance across the TPS changes smoothly when I open and close the valve.
Mass air flow sensor
The MAF appears clean, but I wiped off the contact anyway. Not sure how to test this one. Blow across it and check for a change in resistance?
I checked that the battery (-) was properly grounded to the chassis. In this post, someone suggests that an improper ground, combined with an older battery (or one that's been sitting for a month?) can cause "a relay to drop out". How can I look into this?
Today, I also pulled all the ignition wires and cleaned the contacts, both on the distributor and spark plug end. Some of the spark plug contacts seemed to have a little gunk on them. I also cleaned the "brushes" inside the distributor cap, which had a bit of build up on them.
After cleaning the contacts, I put everything back together and tried again. Here is a video (sorry for the lighting.) Surprisingly, on the second try, the car actually idled! I pushed my luck by touching the gas pedal, and that killed it. But considering how much better it did today (actually idled for a few seconds), I am considering replacing the ignition wires. But then what would the pedal have to do with it?
Has anyone seen anything like this? Taking suggestions.