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Vacuum issues Help

BeardyRocker

NAXJA Forum User
Location
Netherlands
Hello everyone,

This is my first thread here and I hope you are able to help me. I have a '92 XJ 4.0 manual with vacuum issues. The idle seems to be rough or looping and I've been trying to fix the problem, without the result I was hoping for. My RPM indicator says that the idle is around 1100. But also tends to misread from time to time. When applying the brake it seems to fluctuate and go up.

What I've done so far:
- TPS replaced;
- Throttle housing cleaned and new gasket installed;
- IAC replaced;
- Intake/outlet manifold gasket replaced;
- Vacuum lines replaced on intake manifold to MAP sensor, valve cover and fuelrail;
- Brake booster replaced except of the vacuumline.

As I said, so far no dice. The computer doesn't give a error. But after I replaced the gasket on the intake/outlet all seemed to be fine. But after a while the idle went up again and doesn't want to come down and stay stable.

The next thing for me to do would be to visit an expert mechanic, including all costs. So I hope you can give me some advice on how to proceed.

Thanks in advance!
 
I suggest you go back and retorque the intake/exhaust manifold bolts. They can loosen up after a few heat/cool cycles.
 
When a vacuum leak is suspected, I use spray carburetor cleaner, with a nozzle, to lightly spray around the manifold and other possible leak sources, if a leak is sprayed, the idle speed will temporarily increase.
Keep a fire extinguisher available.

A smoke machine is probably the best way to find a leak but not something most have around.Youtube has all sorts of homemade smoke machines, use them at your own risk.
 
..........When applying the brake it seems to fluctuate and go up.........

This indicates a faulty brake power booster,
or perhaps the booster check valve.

Is there a hissing noise under the dash,
near the brake pedal, when applying the
brakes?
 
Maybe unplug the hose that goes to brake booster.
Close the hose with tape or something to make it 'hermetic', and check if it helps.


Also it may be the orings on fuel injectors.
Use brake cleaner spray or something similar and spray there to check.


Your EGR is working?
 
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