'95 850 T-5 Low Idle Vacuum

[sion]

Hi VS'ers

Some weeks ago, I fitted a boost/vac gauge to the wagon, discovered an almost invisible large split in the IAC hose in the process & was happy to observe a Park idle reading of 21 inches hot - very healthy. The car went the best it has ever gone following the hose replacement which correlated with the vacuum reading. Idling in drive, the reading was 18 inches hot.

A couple of weeks later, I drove the car (wife's daily driver) and noticed idle vacuum had dropped to 17 inches in Park. Fuel consumption is up (9.5L per 100km on a long road trip last w-end), no doubt due to the ECU richening things up & idle quality is not as smooth as before - yes, I have another vac leak, but I'm damned if I can find the bugger.

I've just done a full PCV service, replaced all elbows & vac lines & checked the turbo hoses. I've also removed & plugged fittings at the tree & the cruise to see if those lines are leaking. No change.

For all you 850 experts, are their any other known weak spots in these systems I should be looking at? I was thinking of an under/behind dash inspection next.

Thanks in advance as always.

[AlvinL]

The items that come to mind to hold vacuum.

- EVAP purge valve

- brake booster

- CBV valve

- turbo boost gauge

- EGR valve

- EGR vacuum control

- Fuel pressur regulator (fpr)

- boost control solenoid

I'd disconnect the line at the source and 'suck' on it to see if it holds vacuum. That's just a simple test.

[sion]

Thanks Alvin.

No EGR's on our spec cars, so that rules that one out. The turbo boost gauge line is also ok & I plugged the line to the canister to check that also - no change in vacuum at idle.

I will investigate the evap canister more though, as I thought that may have only served as a vent/filter.

On the CBV, is this a common failure & something which would drop vacuum by the 4-5 inches my engine has?

Thanks you.