Dip at idle, surging while engine braking, rough cold idle & occasional code
 

My justa (130K miles) is a commuter car and my commute is about 50 miles one way. For anyone familiar it's the Ortega Hwy. 1400' up the East side of the mountain, 2600' down the West side of the mountain. MPG's are consistently 33-34 for the commute. The following issues have all come about in the past 3-4 months

Dip at idle - When I come to a complete stop, the engine drops to idle then dips down to 400/500 for second and returns to idle.

Surging - I use this term loosely as it almost seems to be the opposite. On the way home the decent is 1200' over 5 miles. I normally keep it in 3rd or 4th on the way down. The engine used to continue to gradually rev up if I didn't hit the brakes. Now, the engine dips 100/200 consistently when I don't give it gas.

Rough idle - Only occasionally does the engine idle roughly. It's seemingly sporadic, but it's definitely noticeable and something new.

Code - I'm a bone head and forgot to record the code, but it's definitely caused by a lean condition. I'm pretty sure it's 'system too lean (bank 1)'.

My two thoughts are O2 sensors and walnut blasting. The O2 sensors are a shot in the dark. I know walnut blasting is done on turbo motors, but my symptoms are similar. Although I didn't read about anyone doing it to a justa.

Any thoughts or suggestions about what I could check or try?

Sounds to me more like a brake / vac line issue ?

Brake booster uses vac line, maybe air is entering system there...

Maybe concentrate your attention to this area ?

Just a thought.

Attachment 129352

Thanks for the suggestion, I'll start there it's cheap enough. I'll pick up a can of starting fluid on my way home.

You were spot on. :thumbsup: The issue was a vacuum leak. I checked all the hoses last week and everything checked out. This weekend I changed the oil and noticed the oil cap would not tighten, but would continue to turn. I made a replacement seal (I made one a year or so ago, not sure if there was one originally) and the aforementioned issues went away. After two days of commuting I can confirm the engine performs as it should.