Nissan Repair: 89 Sentra will not idle, nissan sentra, air control valve

Question
Our 1989 Nissan Sentra stalls while idling but idles great if you slip it into neutral. Lately, it has also started to hesitate at highway speeds - but only stalls while idling in gear.
The problem seems to be worse in warm weather and worse after the engine warms up.
The problem almost goes away completely if we burn 94 octane gas - returns immediately if we burn 92 octane or less.
Can you suggest things we can try to solve the problem?
Thank you ...

Answer
Bill,

I would inspect and replace the spark plugs first.  Second, I would make sure that the the throttle body is clean and the idle air control valve is not plugged.  Inspect the timing to make sure it is correct since you say the engine messes up with low octane fuel.