Vacuum/Pressure Advice
 

My car started to idle jumpy and the vacuum at idle dropped to 18.5~19+(used to be over 20), so I went looking for the source, thinking it was my I/C or boost side hoses.

I pressurized the intake track from the front of the turbo to 15psi, and the only place I had leakage was out of the air breather on the valve cover.

I checked the PCV, and nothing is passing it.

Essentially air is getting into the valve cover, and into the oil sump as witnessed by gurgling oil up the dipstick hole if I hold my finger on the breather hole.

It is not a rush of air, but a slow bleeding out. Other than the oil return from the turbo, which I am about to investigate, can anyone think of another route other than valve seals?

Not yet 80,000 miles on very well maintained motor.

Motor Guys?

When you did this was the #1 @ TDC and all the valves closed?

Also did you remove your rad cap and look for bubbles?

Neither, but it is still set up so that I can do so in the morning, and will.

Might do a leakdown test on all cylinders. That will narrow it down quite a bit.:)

any oil in your coolant or vice versa? if it's the head gasket, let me know, i have some recommendations and tips that might help you.

No bubbles in the radiator, but the level does look higher in the bottle than normal(Maybe just my recollection). Oil looks clean.

Is there a TDC or other position that all the intake valves are closed?(few rotations?)?

I'm at TDC on #1 and getting full airflow out of #3 with the plug out. Don't want to pull the valve cover unless necessary.

I was able to get a decent idle just below 1000, but vacuum was the question that started me looking.

UPDATE:

Pulled off the turbo oil feed and return lines and blocked them at the turbo. Holds air pressure MUCH better now. Still a little leaking somewhere because there is a very little coming out of the breather in the valve cover and when I cap that with my finger, I can hear "glugging" as air passes the oil in the turbo return line that is laying there open to tank.

Takes a minute to drop from 15 to 10psi, then a lot longer to get to 5psi. Maybe it's just worn valve seals.

It was worth pulling apart as much as I did 'cause the hose on the return line is embrittled and ready for replacement and the water in my radiator overflow has shit in it(25000 miles since a flush), so time to do something about that.

Still doesn't solve my vacuum drop problem. Any suggestions.:sadwavey:

FWIW; I had posted the question about all four cylinders having the intake valves closed at the same time on MNet and got a response that it doesn't happen. I left an update there also.

are you getting excessive oil in your valve cover breather tube?

None. I've got a filter on it to atmosphere and it's dry.

Follow my logic please:

If I have no leaks to speak of while pressurizing the whole intake, but still have less vacuum at idle than normal(still within Mazda spec), does it follow that there might be a reason that the throttle body is not closing or is bypassing somehow?

bizarre. time for a p&p'd head! ;)

think your gauge could just be off? Have you done a compression check?

Two gauges, one electric, one mechanical agree with each other. Have not done compression check.

Unplugging ISC connector raises RPM and vacuum goes to 20.

Could it be a leak in the ISC then? Or in the hose? What about the seal at the bottom of the TB?

Dave,

Just pulled the throttle body off a few minutes ago. Not too much gunk, but it looks like the butterfly may have been stopping at two different levels. I'll post further on what I find when I pull it apart and clean it up. Now to locate a gasket.

My normal parts places have no gaskets; B6S7-13-655 for the throttle body.

Any ideas???

Your local auto parts stores should carry some fiberboard blanks to cut your own. Interim option is to cut one from oilboard. No need for the steel or diamond laminated ones for the TB.

When you did the vacuum check, any type of rythmic needle bounce would have pointed to a single cylinder problem ... valves, rings, or ignition. After checking for any vacuum leaks suggest using the vacuum gauge to set the idle. After engine is fully warmed up, set the idle vacuum to the highest setting where the needle sits rock steady. More accurate than trying to read the stock tachometer.

If you have an additional boost loss, would point to a vacuum leak also and not indictive of other engine components.

Well, I found a gasket that I'll have on Wednesday, but didn't want to wait. I figure for the price of the gasket, I should compensate myself 50 cents an hour for my labor on the one I made.

The vacuum got a little better, but the erratic idle remained.

I started thinking that since my fuel pressure seemed to drop off more recently between runnings and my logging of AFR at idle seemed a little strange, that maybe I had a defective injector. I put in my original 1.6 injectors and the idle smoothed out. Leaving the car set for awhile, the pressure didn't drop. Getting some newer 1.8's from Ike and I'll flow test for the best four before re-installing.

Still between 19 and 19.5 on vacuum(used to be 20), but smooth idle. Guess I'll need to wait until it gets worse to find it.:ugh2: