When I got this car, it had been sitting a while and the main reason for that was that it stopped running. When I got hold of it, my father had tried his hand at fixing it and that method is to remove stuff until it works. After convincing him that I really wanted the car I was able to fix a few items that made it run significantly better but there was still an issue with the engine idle.
Initially I replaced the gas cap to make sure the tank was breathing correctly and then I found that the O2 sensor was corroded so that was replaced as well. Right away the car woke up and I could drive it with more responsiveness and speed than before the O2 sensor was changed.
The issue that would haunt me for the next three years was this: When the car was cold, but not freezing cold, it would start and then idle up and then down repeatedly until it was really warmed up. If the RPMs were not high enough on the idle down it would just kill the engine. So you either had to keep your foot on the accelerator until it warmed up or you had to drive off with it and hope you didn’t have to stop because if you did and the engine wasn’t hot enough, it would kill the engine. However, when it was in the winter time and the engine was super cold it would start and then go into high idle and stay there. Once the engine warmed up then it would start cycling again between high and low idle and then die. Only after warming it up further would it start to actually run at a regular idle.
This being the carbureted model, the diagnostic paths to figure this problem out were really daunting. It wasn’t until I purchased the Nissan Sentra Shop Manual on eBay that I was able to get more into the processes of finding an answer. The Haynes manual is of no use considering there are so many variations of this car. Even with the best documentation it still required me to actually understand how to follow it all.
Thinking it was temperature related I tried replacing the coolant sensor but that made no difference. After deciphering more of the Shop Manual I found the test to tell me what direction to go in. It was either a solenoid or a vacuum issue and when I tested the solenoids they all came back okay. Without someone to help me, I didn’t know how I was ever going to figure out the vacuum tests.
What is eventually came down to was performing one maintenance step that I had recently completed, setting the valves. My mechanic said that some of the gaps were really tight so that meant that some of the valves were open when they shouldn’t have been and now after the correct adjustments the car runs better than it has since I replaced that O2 sensor. You can still tell there is a little variation in the idle but the engine doesn’t die anymore.