RWD - Vacuum Leak at Throttle Body

Volvo RWD 700 Forum

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Vacuum Leak at Throttle Body 700 1989

I'm trying to solve a rich mixture problem with my 1989 Volvo 740 Turbo; car has been in my family since new and has only 104,000 miles (in 27.5 years!), good body condition. Car is currently getting approximately 12.6 MPG in mixed driving, sooty tailpipe and spark plugs.

Previous relevant work:
1. New air filter and spark plugs (NGK Platinum) approximately 4000 miles ago. 2. Coolant Temperature Sensor and Coolant Gauge sensor replaced a few months ago, along with thermostat which had apparently failed (hard to tell with non-working gauge).

What I've done lately:
1. Cleaned MAF Sensor with CRC MAF Sensor Cleaner. Made car run slightly smoother.
2. Sucked on vacuum hose connected to fuel pressure regulator - holds vacuum, not leaking fuel through diaphragm.
3. Visually checked all vacuum hoses, all are OK.
4. Borrowed a smoke tester, hooked it to the brake booster vacuum line (plugged the intake hose just downstream of the MAF) and found that smoke was coming out at the Compressor Bypass Valve (CBV) and through the spring on front of the throttle body! (see pic)

The leak at the CBV may be due to one of the two large hoses being slightly loose; the valve is very oily/dirty and I don't see any cracks in the body of it, so I will remove it, clean it up, reinstall and tighten the hoses. Hopefully the hoses will still be usable, as it's probably hard to find replacements.

The throttle body leak "through the spring" may actually be due to an ovaled out hole where the shaft goes through the throttle body. Has anyone seen this before? Is there a straightforward solution for this? I know on the older Volvos with SU carbs, this was a problem that could be solved by drilling out the hole and installing an appropriate bronze bushing. Perhaps a used part is a better solution?

1989 Volvo 740 Turbo
1970 Volvo 1800E


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New Vacuum Leak at Throttle Body [700][1989]
posted by  Dorsal900  on Mon Apr 17 20:47 CST 2017 >

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