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You keep saying head but neither of the booster lines for the clutch or brake boosters come off the head, they come off the upper intake manifold (or plenum).
Ah shit you're right, I made that reply while waiting to respawn in a game and just went with what I'd said before. I'm big dumb. 🤦‍♂️
 

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Discussion Starter #42
both my check valves are installed correctly and working. i took them off to make sure i only get flow in one direction.

any other ideas?

the only thing i haven't dive into is fuel. can bad fuel related components cause rough idle?
my idle will surge between 200-1500 rpms.. at lowest it will almost cause the car to stall.

do u guys know any simple test without additional required tools or equipment i can do to check my fuel if fuel can cause rough idle?

i am currently out of ideas on my vacuum leak.. is it possible to have maybe a crack on the wastegate??? crack on the motor itself???
 

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To confirm, when you pulled the check valves off their respective plenum nipples you could suck(vacuum) through them, and not blow(boost)? Did you check the hoses and hard lines for the clutch and brake boosters as well? Any easy way to test to see if it is the wastegate itself would be removed the line and plug it, if it doesn't leak that's your problem.
 

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Discussion Starter #44
plugged wastegate line and yes it is still leaking, can hear it underneath the turbo...

the only thing i haven't dive into is fuel. can bad fuel related components cause rough idle?
my idle will surge between 200-1500 rpms.. at lowest it will almost cause the car to stall.

do u guys know any simple test without additional required tools or equipment i can do to check my fuel if fuel can cause rough idle?
 

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Okay so AFAIK the only other lines besides the wastegate, clutch/brake booster lines(assuming you actually checked those past the check valves) that run around behind the turbo is the cruise control vacuum line. Does your cruise control work?
 

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Okay so AFAIK the only other lines besides the wastegate, clutch/brake booster lines(assuming you actually checked those past the check valves) that run around behind the turbo is the cruise control vacuum line. Does your cruise control work?
The cruise control vacuum line comes from its own little vacuum pump and is not connected to the rest of the system. As such it wont be pressurized during a boost leak test.

The only thing under the rear turbo is the exhaust manifold and exhaust. The rear valve cover could leak and perhaps sound like its coming from under the turbo (there will always be some air that gets into at least one piston and past the rings into the crankcase but it should be minimal).
 

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1991 VR4
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The cruise control vacuum line comes from its own little vacuum pump and is not connected to the rest of the system. As such it wont be pressurized during a boost leak test.

The only thing under the rear turbo is the exhaust manifold and exhaust. The rear valve cover could leak and perhaps sound like its coming from under the turbo (there will always be some air that gets into at least one piston and past the rings into the crankcase but it should be minimal).
Good point, and you can just take the oil cap off if you want to make sure its not crankcase pressure leaking that you are hearing.
 

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Discussion Starter #48
thank you ross and striker for the additional help.

my cruise control does not work. i have sprayed the hard lines and the does not seem to be any leak.

i redid my rear valve cover and it was loose before. its still the same. still hear the sound. so if i open my oil cap, i should not hear the leak in the rear anymore if its crank pressure? should i have something like a towel there or anything i dont know if oil will start spouting out...
 

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thank you ross and striker for the additional help.

my cruise control does not work. i have sprayed the hard lines and the does not seem to be any leak.

i redid my rear valve cover and it was loose before. its still the same. still hear the sound. so if i open my oil cap, i should not hear the leak in the rear anymore if its crank pressure? should i have something like a towel there or anything i dont know if oil will start spouting out...
You can open the oil cap without putting anything there, its not going to spray oil out from a pressure test. And yes, that will be the path of least resistance for crankcase pressure, so if you have the oil cap off, that would eliminate the other leak you are hearing as coming from crankcase pressure.

There are a whole bunch of vacuum lines back by the rear turbo, especially if you have not done vacuum reduction and still have emission controls in place. I can almost guarantee it is one of those...



 

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I just remembered you randomly said something about air getting into the exhaust which was random....can you tell which side of the rear turbo the air is coming from? I don't much about how the EGR system works, other than I plan to remove it shortly, but this might be your EGR system if it is still intact. The EGR valve is on the passenger side, directly behind the plenum, while the EGR pipe is on the driver's side and comes off the back of the plenum and goes down to the rear O2 housing/precat area. You might have a partially stuck open EGR valve, missing/damaged gaskets on the valve/pipe(3 total, 1 valve, 2 on the pipe), or a combination of both. Maybe give those a look?
 

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