Those aux air valves have a near 100% failure rate after all these years. Sometimes they stick open, sometimes shut. Sounds like your could be stuck shut. You could try reviving it (can't take it apart, but you could take it off the head and clean the air passages well, try to lube it, cycle it with hot and cold water) or replacing it. They aren't particularly cheap - probably around $100 or so by now.

When these are stuck shut they usually don't make the car particularly hard to start, they just idle too slow to run until the engine warms up. It might be some other minor fault in the FI system throwing off the mixture. Luckily the D-Jet system is quite simple (compared to newer systems) and there are only a few sensors you need to check out with a multimeter. The best practice in this case is to pull the big multi-plug off the computer and use a multimeter to check readings there - that way you test thw sensor AND the wiring as well. The wiring is the problem about 1/3 of the time in my experience. If you find a problem at the computer check again at the senso to determine where the fault lies. Here's a link that has the readings you should expect from the sensors. You would need to consult a wiring diagram to determine what connectors on the multiplug correspond to the sensors.
http://www.icbm.org/erkson/ttt/engine/fuel_injection/d-jet.html

My guess on your fuel gauge - the voltage reducer gadget is fried. The 140 gauges run on low voltages, but get straight 12 volts briefly when you first turn on the key. This makes the gauges jump up too their readings, rather than creeping up slowly as they would otherwise. Sometimes the voltage reducers stick and send 12 volts constantly through the gauges, which will fry them in short order. Although if that was the case you should also have the same problem with the coolant temp sensor - if it is still the original electric one. You could get a new gas gauge and hook it up, then watch it carefully when you first turn the key on. If it pegs immediately and stays there turn the key off and unhook it until you get a new voltage stabilizer. Its a little silver relay gadget that hooks to the back of the instrument panel.