I have an intermittent problem that I've been going to great lengths to try and solve. When I come to a stop during the first 10 minutes of driving, the car will intermittently (not every stop) idle low. It only does this in cold weather (below 35 degrees). It's low enough that it feels like it could stall but it never does. I have no idiot lights currently and when I checked the computer there were no codes in any sockets. When I floor the car I can feel some surging during the acceleration. Correct me if I'm wrong, but this is why I think it's a vacuum leak problem. I feel like I've looked over every single elbow and plastic tubing and have found no holes. The car does have 107K miles and some of the plastic tubing and elbows are original (I’m original owner). Could an elbow that's collapsing cause this problem? Should I just replace all elbows and plastic tubing? If that's the case does anyone know where I can get all of the elbows and tubing for a reasonable price? Could the hole clogged up to the EGR valve cause this problem? Finally, is there any tool I can hook up that would give me a good indication that I do indeed have a vacuum leak?

Thanks in advance
Scott K

1994 850 Turbo
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Scott K - 1994 850 Turbo

I use carb cleaner to check for vacuum leaks. Starting fluid is too volatile to be used anywhere near ignition parts.

There is a small vacuum tube under the inlet manifold of the turbo 850s that is prone to faÿlure and VERY hard to get at. Approach from the belt end with a mirror.

Another poster mentioned volvospeed.com, they have a very good page on this.

Is this the one that is documented on Volvospeed? The one by the power steering pump? If so I don't think I have one there. I have searched and searched for that one and I could never find it. I wonder if it just doesn't exist on a 94 Turbo.

Scott
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Scott K - 1994 850 Turbo

Ditto! I could never find that one on my '94 850T. Came to the same conclusion as you.

An effective way to determine a leak is to spray starting fluid on the hoses one by one. If there is a leak, the starting fluid will get sucked in and cause the engine to race a bit for a second.

Because yours is a Turbo, I woudl look through all the posts regarding rough idle, cold start problems, etc. There is a bunch of info regarding the Intercooler hoses collapsing and filling with water. That may be your problem.

Reading through some old posts and I've heard people mention that O2 sensors could cause this. My O2 sensors are original, is it true that you should just replace them at 100K miles? I still get good MPG (about 19.5 city and 28 highway), I thought when the O2 sensors were going you would see a noticeable decrease in MPG and even possible a check engine. I'll look into the intercooler hoses; I should probably replace those anyway.

Thanks
Scott
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Scott K - 1994 850 Turbo

Go to volvospeed.com - there is a nice set of instructions, including photos, on how to find a vacume leak.

From what I have seen, the plastic hoses are not prone to failure, although they might get clogged up under certain conditions. The rubber connections and elbows are the weak links.

A couple of troubleshooting suggestions-
*** If you disconnect a really bad vacume hose, you might get no changes in the way the engine runs - this depends on the function of the hose.
*** If you block the source of vacume to a bad hose you might get a change in the engine for the better.
*** I have seen mechanics spray water on suspect areas, the water seals small holes temporarilly, curing the problem - once again depending on the function of the hose. Some times a noise can be heard when the water is sucked into the hole.
*** Before the cooling fan operates, you could try a small source of smoke to detect a leak.

Do a search on vacume leaks, I read a decent tip on finding vacume leaks, but I forgot what it was!

Has anyone tried putting a little pressure on the vacume system and checking with soapy water? Can this harm anything?
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3 8s & 2 7s 725,000 miles total

I would be tempted to keep all the elbows and connectors (unless there is obvious damage) and just replace the vacuum lines. Why not pull a small piece of the hose off and measure inside diameter or just take it with you to the auto parts store and do a visual size match. The hose is not that expensive. You may wish to replace with silicone rubber hose for longer life; not that much more.