'93 Legacy Idle dives when switching gears

[AKDave90]

Hey y'all,

 

So I have a '93 Legacy, and it has recently been doing this funky idle dive. When warm and idling, the RPMs hover comfortably around 500. While driving (most often when engine braking), when I depress the clutch either to coast or shift, the RPMs dive down close to 0 then fluctuate between 500 and 0 for a few seconds before settling in at 500 or a little less. It doesn't always do this, and it has no fluctuations when idling at a stop light.

 

This problem was more of a curiosity until the engine actually died on me yesterday. I was camping around 5,600 ft at the end of a small mountain road. The car restarted fine, but as I descended (using the engine to brake), the diving idle kept happening but without killing the engine completely. As I descended back into the city, the problem seemed to return to its normal "once in a while" standard. Could it have something to do with altitude? I want to get this fixed b/c I need to drive up to Alaska in January, and I don't want to get stuck somewhere.

 

Thanks for any help you can give.

Dave

[bstone]

Vacuum leak.

[lmdew]

Neutral switch on the trans tells the ECU when the trans is in between gears.

The wires come to the top of the trans right behind the engine so it's easy to check with a meter.

[ferret]

Neutral switch on the trans tells the ECU when the trans is in between gears.

The wires come to the top of the trans right behind the engine so it's easy to check with a meter.

I would suggest that,, but I am not certain the 90-94 had one. I AM certain starting in 95 it was there on the 5 speed. But it WOULD give these symptoms, IF your trans has one.

 

If it does, it will look just like the backup light switch mounted on the drivers side of the transmission.