My car at idle is running 17 in HG but the needle is very shaky. does this mean that I have a vac leak or that something else is wrong with the car. I am contemplating replacing the engine but i would like some outside input from somebody with a little more knowledge.

thanks
Adam

 

Where are you measuring the vacuum? Off the empty nipple on the right side of the UIM?

If so you may just need a restriction in the gauge tubing to damp out the pulsations.

What is your idle speed? Do you have any other symptoms of engine problems?

If not, it's probably just the gauge responding to normal intake pressure pulses.

 

I would say its the gauge. 17 hg is prity good vac at idle.

Jeff

 

I second the gauge theory. I had a gauge that bounced around guite a bit at idle. Swapped gauges on the same motor and the vacuum reading smoothed out.

 

yes off of the extra vac nipple on the uim.
the car does have a sticking idle which is related to the brakes most likely the check valve. and a little studder of the engine that i have not been able to figure out yet
the car is stock with 65k on the odo and new silicone lines and check valves for the rats nets.

 

I'm guessing that your stutter off idle is related to the brake-boost check valve which, if faulty, allows air to flow unchecked between the UIM and the booster unit, screwing up the mixture. This can happen because the ECU signal from the TPS can not tell the ECU everything it needs to know about the volume of air flowing thru the UIM.

This, however, is probably unrelated to the gauge flutter.

Dave

 

I forgot to install the restriction in my boost gauge and the needle pulsed constantly. Most boost gauges come with either a screw-on or an integrated restriction. The central orifice in this restriction should be only about 2mm.

 

this is wat it is, i have no doubt. your boost has a healthy reading