Posted 11 February 2011 - 05:14 PM
Had a car come in this past week for a surging idle problem. Toyota Camry 1996- regular I4 engine. It was idling between ~500-1100 RPM. I pulled the code on it and it indicated a lean code. Drove the car around and the surge disappeared while the engine was under load, generally indicative of a vacuum leak. It took me a while to trace it, but I found a leak in a vacuum hose at the bulkhead. What had actually happened was there appeared to be some sort of electronic idle vacuum gauge (sorry, I can't be more specific, I couldn't get access to the dealership that day for the part, so I don't know what it was and the part number has now been lost to me- it's on the same hose as it comes off the brake booster) and the plastic neck coming off of this device had broken off and lodged in the hose (the hose was now disconnected due to this).
What's strange is, the surging idle went away even with the engine idling as soon as the fan cut on. The engine would be surging in idle, then you would hear the fan relay click, the fans would cut on, and the idle would stop surging and stay at about 1000 RPM.
Since I couldn't replace the part immediately and they needed that car, I made a temporary fix which I have the feeling they are going to allow to be a complete fix. I extracted the neck lodged inside the vacuum hose and disconnected the sensor from its harness. Where the two surfaces once mated, I took my soldering gun and melted the plastic edge around the neck remating the sensor and neck once again. Reconnected everything and the car started up perfectly with the surging idle cured.
So I have two questions:
1. What is this "electronic idle vacuum gauge" that I'm talking about here?
2. What is the link between the fan relay cutting on and the surging idle disappearing? The link between the two is not immediately obvious to me.