Where should the economy gauge when the car is at idle? While idling in gear it moves towards the middle. Does this indicate a vacuum leak?

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1989 300CE

In park, at idle, the vacuum gauge should be pegged full to the left if there are no leaks anywhere.

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1991 300E - 212K and rising fast...

What about when in gear?

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1989 300CE

With the engine warm, just a little bit off the end line - nowhere near the middle.

Right, if the gauge is not fully on the left side at idle then it indicates some problem, provided tubes are properly plugged.

Idling in Park, economy needle should be pegged to the left side of the gauge.

Idling in gear, economy needle should be about 1/8"-1/4" to the right of the peg on the left side of the gauge.

If it is is anywhere close to the center either in park or in gear (idling), there is a significant vacuum leak somewhere. If that is the case, you should probably have other symptoms of the vac leak though.

Cheers,
Gerry

When you have the AC cranked up, aux fan running, headlights on and other stuff, it puts enough strain on the engine to move the econ guage. I've never seen it 1/2 way, but it can get as far as 1/3 the way across on my 300e.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth