When cleared, fault code 1-1-3 (short term lean) re-appeared at 10 min of gentle idling from cold engine. Then, I cleared it and immediately restarted engine. CEL appeared at exactly 3:20, two times in a row.
Generally, idle is stable but occasionally drifts up to 1200-1300 then back down. The engine, though, doesn't seem to sound right during idle. Normal performance while driving.
1) I think I have a vacuum leak on pass.side of intake manifold gasket. How common is that?
2) Any tips on the replacement job?
3) Anything else that should be replaced while I'm "in there?" (other than Fuel Inj. o-rings)
4) BTW, is it possible to take a voltage reading of oxygen sensor with it totally disconnected from harness? I thought that sensor output voltage would be the same with and without any power from harness, but I don't see anywhere that suggests I can test sensor disconnected. (I want it disconnected b/c I don't want to "backprobe" w/ such tiny voltages!)
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Two 1995 854 GLT's (w/ manual transmissions)

Hi,
HO2S with ignition on gives 0.45-0.46V
On idle 0.1V -0.9V when engine is hot, Low is for lean, high for rich running.
one information I've seen says also for cold sensor approx 3 ohm, hot 13 ohm.
all above found when looking for 850-94 NA engine.
br Tapsa

Those sadistic Volvo engineers could have placed the vacuum line in a better spot. If you have long, bent needle nose pliers to tke off the hidden clamp, then you don't need to take off the manifold. The vacuum line is part of the oil breather system, so the only advice I will give is to replace the entire line while removing the manifold.
You don't need to remove the fuel injector rail, it adds a lot of additional work with the injector removal that isn't required. It is also a good time to remove the vacuum tree and throttle body for through cleaning and inspection.

If you have access to a good scanner, plug it in to the OBD port in the center console and get real time readings on the O2 sensor - after the vacuum leaks are taken care of.

Use a butane cigarette lighter, without flame, and check for leaks around the manifold. If there is a leak, the butane will cause the idle to change.
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My name is Klaus and I am a Volvoholic.

1) I wish it were as simple as a leaky hidden-in-BFE-under-manifold-elbow. My 850 doesn't have that elusive hidden elbow (5-speed, built 10/94). The leak, I believe is in the intake manifold gasket. How common is it for the gasket to leak severely enough for a "short term fuel lean" fault code?
2)Unfortunately, the 850's didn't have an OBD port in the console until later.
3) Could a vacuum leak cause a well functioning O2 sensor to have these readings: little variation at idle, around 0.35 to 0.45 volts; at almost full throttle, would jump to 1.1 volts (!?), again w/out much variation. Never below 0.35 volts and never above 1.2 volts. >> ie, should I suspect the oxygen sensor also?
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Two 1995 854 GLT's (w/ manual transmissions)

Your are lucky, that elbow is a pet peeve of mine. And yes, manifolds do leak, there have been many NA engines that get their O2 sensors messed up that way.

Removing the manifold isn't that terrible, but get a new gasket from the dealer, the FCP Groton gasket I got from them isn't worth 50 cents! Also a very good time to clean the throttle body.
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My name is Klaus and I am a Volvoholic.

Klaus,

What a great idea, only I'm thinking a propane torch (less flame) that has that nice extension, ideal for getting into tight places!

Jerry
01 V70 T5a