I bought a 940 to learn how to work on cars and have a reliable daily. So far, it's great and I've changed spark plugs, oil, and the air filter, and cleaned out the mesh grill up top. But I have no idea what this vacuum line is in the picture (with the break/leak directly in the middle). I just know it's a return and I'd like to know the part so I can order another.

 

That is the intake air pre-heater tube. Note the other end goes to the air filter housing. It takes heated air from around the exhaust manifold and routes it into the air filter below ~40 degrees. But - Typically the air box thermostat goes bad and gets stuck in the hot air mode - helping to fry your air mass meter! (look in the air filter housing - note a flap that directs preheated air or fresh air from in front of the car. Is it stuck in the hot air mode?)

Leave the hose alone, and if stuck in hot air mode - disconnect it from the air filter, and if desired take the flap out to force it into cold air mode.

The preheated air helps prevent icing in the intake when very cold outside -

 

Thank you for the response. Why shouldn't I replace it?

 

You certainly can replace it if you want to - if the air box thermostat is working properly, sending cold air to the engine when it is warm outside. (but i'll bet it's not)

Or you can save your hard earned dollars for something that really needs to be fixed.

 

I couldn't find the flap, but I did find the MAF and decided to spray that with some MAF cleaner. That didn't seem to help my rough idle. Any idea what the flap looks like or what I can search to find it? I appreciate your advise!

 

So, it looks like I need to take the entire air filter housing off and then inside would be the air box thermostat which I can replace? I'm confused what/where the flap is. Thank you for your help.

 

Rough idle can easily be caused by an air leak - sometimes the intake manifold gaskets break/tear due to heat expansion and contraction, and then an air leak is created. - Use carb cleaner and check for air leaks at the manifold gasket.

Or - unplug each injector and notice the change in idle to help figure out what cylinder is causing the rough idle.

 

where are you located? as Hoonk noted the fat hose is not a vaccuum line so it won't be in play for your rough idle issue. Note that hose is no longer available from Volvo but web stores like FCP carry generic after market tubing. If you trace the hose you will see it goes from the intake manifold to the air filter box. Google Volvo 9135184 to find a Volvo parts web store with a diagram or you may find something on Volvotips.com but its easy enough to look for a flapper valve that opens when cold and shuts when hot. You don't want that valve to be stuck open pulling hot air in except on a very cold morning start up. If you live iin an area that doesn't go well below 32F you won't really need the part at all...

 

I'm located in the Mid-Atlantic, so it hasn't got very cold yet. I notice the more I run the car the worse the sitting idle gets so this makes sense. Before I go digging in the wrong place it appears the flapper valve is inside the airbox right? If so, I think I can easily find and replace this. So far everything has been easy to repair on this car. I've been surprised. And everything I've done has made the car run a lot better. The previous owner, one owner, had really good service records up until the end. The air filter had mold growing on it, the spark plugs weren't terrible but weren't gaped correctly, the hose was completely disconnected as the exhaust manifold and the belt wasn't tensioned correctly on the alternator. All of these adjustments seemed to help a lot, with spark plugs making the most impact. But there is still a rough idle (went from all the time, till I've been driving a while and I come to a stop and it goes low with the smell of fuel). It doesn't overheat, coolant levels are good, oil is good, and spark plugs didn't show anything concerning.

 

Your broken intake air preheater tube has NOTHING to do with your rough idle.

 

have you scanned for codes? I'd be searching for crusty vacuum lines and I'd certainly check out the source for the gas smell - could be the evap system (which draws fuel tank vapors into the intake to reduce emissions). If your visual test doesn't find anything I'd have a shop do a smoke test as there's lines in hard to see places including the evap purge line that runs all the way back to the charcoal canister... Also, have you checked the PCV system?

 

Update. First, I want to say I got this car for $1000 and i specifically bought it learn how to work on a car.

I did scan for codes and got a 113 code. I replaced the spark plugs/spark plug wires and it runs slightly better. Everything I've done so far has been the following: Spark Plugs, Spark Plug Wires, Air filter (the original had mold growing in it). and oil change. I also found some really nice OEM wheels with brand new tires and no scuff marks for $400 and installed those. Everything has made a slight improvement but here are some major things.

When I got the car, the original owner started it up and I noticed right away the belt on the alternator was flappy. He mentioned something about tightening some bolts and it should be good but he hadn't got around to doing it. I did tighten the tensioner bolt for the belt, but still the alternator doesn't seem to charge the battery. I have to disconnect the battery every week or so and charge it with a trickle charger. I also remove the negative anytime I park. I used a voltmeter to check the fuses for continuity and each one was good. I have a suspicion the alternator or the voltage regulator in the alternator isn't working. For one, the battery is constantly losing volts. Two, the gas tank gauge will periodically stop working, the radio will flicker lights, and the beeping noise to close the door when I start the noise will change pitch. I have located that I have a Bosch ignition system. The ignition coil looked pretty rough when I attached one of the spark plug wires from the bottom of the distributor cap. There is the smell of gasoline around the car.

Anyways, I'm pretty sure that there are a lot of minor issues and I'm interested in tackling them and learning. The body of this car is in very good shape, the car doesn't overheat at all, It was one owner with outstanding service records. It does have a lot of miles. My gut says go for the alternator first. Where should I buy the alternator first and any further advice would be appreciated.

 

OK - Is the alternator belt tight? (and not shiny black rubber where it touches the pulley and not flopping around when running) With your $10 Volt-ohmmeter - what is the voltage at the battery with the car running at 2000 rpms?

If that voltage is ~13.8 volts or so (with a reasonably charged battery) your alternator is ok.

if so NO - don't buy an alternator (without a reasonable diagnosis - I'm certain that if the car only cost $1000 you don't want to spend your hard earned dollars frivolously)

And - IF you need an alternator, I would be cautious buying from the local auto parts stores. Sometimes for "foreign"cars the "rebuilt" alternators may not be the best quality.

I gave my son a 1994 940 that had the Denso alternator. His battery would stay charged when he had to drive 10 miles to work. When he lived 2 miles from work - the denso alternator would not keep his battery charged. What alternator do you have and how far do you drive the car everyday? (the cars with a bosch alternator seem to keep the battery charged better). At my shop I converted a couple of cars (many years ago) from denso to bosch alternators to solve the "my battery goes dead" problem. It was not as easy as it should be - the alternator wiring harness connections are a different size between denso and bosch.

 

Update! I had a friend keep the rpms at 2000 while I checked the voltmeter. It gained volts as he did this, however when he let off the gas the car would do it's rough idle and I noticed a large decrease in volts and then when the rough idle went away the volts would increase. I'm guessing the alternator is fine. I think it's a Bosch alternator but it's hard to tell as it's quite old and worn looking (couldn't get a s/n or part number as it's too faded, but everything else in the ignition system is Bosch).

The car definitely has an electrical gremlin, so I have to disconnect the negative terminal whenever I go somewhere. I do want to point out the body of the car is in amazing shape for having 350k miles so yes, it is a $1000 car but I think it's worth restoring over time (just not all at once). It serves my purpose of getting me to work and back 15 miles each way and saving miles from being put on my F83 M4. Also, a big goal was to learn about working on cars by purchasing this car. Anyways, back to the gremlin. I checked all the fuses for continuity and they're good. Anyways, I work with a couple of engineers (I'm not an engineer myself) and one said to check the solenoid above the starter. And the other one said I should check the voltage regulator first which I then found out was part of the alternator on this car. Anyways I'm a little lost where to start looking for the gremlin and I know it'll be a process however I still need to find the cause of the rough idle too. Oxygen Sensor, Ignition Coil, Distributor Cap? The ignition coil looks pretty worn, but I'm guessing the oxygen sensor is the cheapest? There is also the faint smell of gasoline too. Any help for direction would be great. Should I check the relay's behind the fuse box?

 

Also, Hoonk, I found your post about relay testing 1994 Volvo 940 Fuel Pump Relay Location - Volvo Forums - Volvo Enthusiasts Forum
So, I'm reading through that. Thank you for all your help so far.

 

I guess I could do something like this and check to see if the smell is coming from the charcoal canister area?

 

Guessing can get really expensive and frustrating - that's not really the best way to solve you car problems. And it's probably not your O2 sensor - they can only change the mixture very slightly.

 

And kind of figured that. Throwing everything would eventually solve the problems, but part of becoming a mechanic is figuring out the issues. Any visual inspections I could do to figure out what to do next besides the 113 code?

 

For a rough idle - I would try to figure out what (if any) cylinder is causing that.

Compression test would be a good first step, but if you can't do that - With the engine idling(rough) disconnect each injector one at a time and note the idle drop. If the idle stays the same you have found the cylinder that is not firing at idle. The idle motor/iac/air valve whatever you want to call it - will try to keep the idle speed steady, so you may just have a second or two to determine if the idle is the same or worse.

You can do the same thing pulling spark plug wires - but not really recommended, kinda stings when you get shocked -

 

Okay I'll try this. I don't think it's the charcoal canister as I did some exploration and didn't smell the gas coming from there nor did anything look off.