car has no power off the line. vac is stedy 13" at idle in park, when put in gear it drops to 9". when engin is reved up vac drops a little then goes to 15" and 20" on decel. these readings seem low to me, i checked all vac lines to no avail. any suggestions? are these ok readings for a 2.8 v6 ?

 

Yes its low- you have to be getting a hard brake pedal at idle. It should remain at about 17-18" at idle until you blip the throttle. Vacuum will alway drop when the throttle is applied but when released it should imediately go back to the 17-18" range.

You do have a leak somewhere. It is common for the egr diapham to tear or slit underneath. It is impossible to see with it on the car. This a common cause of the vacuum drop at idle, but not the only cause.

I too have an '87. Is your car looping or surging the rpms at all at idle?

 

Before ya say the offered information is "low readings"
Consider the age of the powerplant, along with the offered vacuum reading information.
Due to engine aging, this could be "OK".
IF ya can't find any leaks, it just could be the engine is aged, on it's way out......
The above reply is very good call on the EGR valve, tho.
I've spent a whole day doing vacuum leak searching. But working on a newer low milage 3.4, it was with better results.
Your egine could need a simple tune up or the coil could be so weak as to not offer a powerful spark to make engine idle strong to give better vacuum readings.
More points/details to consider.
IF YA CRACK THE HARD PLASTIC LINES, ya can patch them with windshield wiper washer hose & spit on the broken plastic parts.
IF your car accelerates ok, aged engine is the problem.

 

thanks ill look at the egr tommorow. car was owned by an old timer. one owner with only 46k miles on it it sat for years. did complete tune up and replaced coil due to weak spark. im kind of thinking its some thing that dry rotted or went bad from sitting. ill let you know. any other things vac related to look at?

 

vac on mine is 15-16 at idle, 17-18 at 1000rpm. Might want to check your timing first.

 

update. checked all vac lines and componets all ok. for the heck of it i pulled the spark plugs and noticed that all three on driver side were slightly coated.looks and smells like burnt oil. three on passanger side looked great. any idea why these three, only on one side? they are new plugs gaped correctly,new wires rechecked with meter,new cap looks good,new rotor. new coil,and 02 sensor. this would probably explain low vac.

 

I doubt that the oil coating would have that kind of impact on your vacuum readings. They are low, even for an aged motor. My motor has 225K on it and still pulls 17 inches at idle, never had the rings done. You definitly have a vacuum leak, whether it be in the intake system/vacuum lines, or in the cumbustion chamber itself.

Have you had the timing chain done recently?

A lot of people manage to screw that up, and it causes low vacuum if it's retarded.

Here's a quick test for you to do with that guage.

Hold the throttle open and keep the motor at about 2500rpm, then go WOT and let it snap back to idle.

You want to see 3 things:
1) ~ 20-22" of vacuum @2500rpm
2) When you go WOT, you want it to go down to 0" of vacuum
3) When you go back to closed throttle, you want to see the vacuum surge to about 25-26" of vacuum.

if you get low reading all the way across, it's a leak or a cam problem

if you don't go down to 0" at WOT, you have an intake restriction(doubt it since this would make you vacuum higher than normal)

if you don't get the overswing/surge of vacuum when the throttle snaps shut, then you have an exhaust restriction. (This is the most common problem associated with low vacuum)