Having your lights on affects vacuum reading at idle

[Stkid93]

If any of you guys are worried you have a small vacuum leak. Just having your lights on will completely throw off your vacuum reading. Turning my lights on reduces it from -10.6 ish all the way down to -9.8 ish.

I have never seen headlights make such a drastic difference before. But then again this is by far the smallest engine I’ve ever owned.

In Any case if you are trouble shooting your vacuum reading literally everything can affect it on this car. I’ve even heard having the radio on can affect it slightly. Hope this helps someone

 

[Alkoran]

Seriously, take your accessport, shove it in a drawer and enjoy your car!

It's normal that the manifold pressure goes up in the manifold as the IAC will open more to compensate for the load on the alternator and the engine thus getting closer to atmospheric pressure.

Also you cannot diagnose a vacuum leak this way because there's no MAF sensor so no skewed air mass reading to be had. That's why our car doesn't have any problem with VTA blow off valves.

 

[Jkaustin91]

Wait till you turn the AC on too..

This happens on my 5.7L jeep too. can even hear it in the exhaust at idle

 

[Dialcaliper]

If any of you guys are worried you have a small vacuum leak. Just having your lights on will completely throw off your vacuum reading. Turning my lights on reduces it from -10.6 ish all the way down to -9.8 ish.

I have never seen headlights make such a drastic difference before. But then again this is by far the smallest engine I’ve ever owned.

In Any case if you are trouble shooting your vacuum reading literally everything can affect it on this car. I’ve even heard having the radio on can affect it slightly. Hope this helps someone

It’s more obvious because any of the larger current loads in the car (A/C, headlights, power steering at idle, etc) in addition to increasing engine load also trigger the ECU to bump the idle speed up as well.