So, I own a '93 Volvo 940 Turbo Wagon. Only major issues I'm experiencing right now is that the cruise control won't work and I can't really figure out why. I've tried playing with some things, but I'm drawing blanks. The little diaphragm that hooks to the throttle cable is in perfect condition and the vacuum tubing for the cruise control is in great condition, no leaks either. Only problem is I can't figure out if the vacuum pump is bad or not. I know the brake lights work, the brake light switches both work and so I'm confident it's not a problem in that area.
Additionally, the other problem I'm having is with getting my heater's vents to open and close. For some reason it's stuck blowing through every single vent and I've taken off the heater control module thing, replaced it, and I've also tried feeling the tubes for a vacuum, but there appears to be no suction coming from any of the tubes. Not really sure what I'm supposed to look for, but it's a little annoying not being able to pick which vent I want air coming from.
Other than that, the only other issue I'm having is inconsistent RPMs. If I'm driving on the highway at about 3,000RPMs, the tach needle will bounce up and down by about 100-300RPMs and I can feel the car revving up and down as well, so I'm sure it's not an issue with the tach. Not sure what all is up and down with my car, but it also doesn't like to idle too well either, when in park or neutral. This is my car and I'm only 17, so I'm still somewhat new with doing these fixes, but I've already replaced the fuel tank pump/sender
Also, would anyone know where/how to work on the PCV and/or EGR system on this car? It misfires from time to time and has this problem where it refuses to accelerate and I have to pull over, put the car in neutral or park, turn it off for a good 10-30 seconds, and the problem usually goes away.
Thanks for any consideration, as I would extremely appreciate any and all help!

 

is it throwing any OBD codes? a 93 940T should have the lh2.4 OBD code display which is a little box foreward of the left shock tower.... Engine and OBD Diagnostic Codes

there is no "PCV" on these cars, instead, they have an oil trap and a hose over to the intake manifold between the AMM/MAS and the turbo intake.

The EGR system is controlled via a vacuum thing thats near that OBD code reader, looks like a little tophat with a coulpe vacuum hoses, one to the intake manifold, and he other to the EGR valve thats tucked in the side of the engine block under the intake manifold, and connects to a pipe that goes around behind the back of the engine and feeds into the exhaust manifold. AFAIK, mostly only california cars even have EGR systems.

the ventilation flaps are all vacuum activated, its a pretty complex system, that stuff all lives under the dashboard and takes a few hours to dig into. first, I think I'd check all the vacuum spagetti tubing off the intake manifold, and replace any that are sketchy. a turbo needs clamps on these, because under boost it has positive pressure.

 

There is a vac line that goes through the firewall on the driver's side, replace it.
It supplies the recirculation and other vent controls.

Honestly, I would just replace all the vac lines, clean the throttle body and idle control valve.
Chances are good that these cheap things will fix your problem.

 

As for the cruise control, good luck with it.
Mine hasn't worked for months.

 

Obviously vacuum issues, even the cruise. The idle surge may be due to intake manifold leak. Look for leaks, listen/feel for air escaping/sucking/hissing-usually it's not that hard-chances are it's in the engine compartment somewhere, not inside.

 

Well, I have this little thing by the OBD code reader that has two vacuum lines running to it. I don't understand what it does, but I know if you suck on one line the motor will start to die. Neither vacuum line produces and vacuum, positive or otherwise. I can't really hear much hissing, although there is some that I can't seem to trace. Not sure where to start, but I'll try about getting some new vacuum tubing, as my car is about 222k miles with all original tubing and etc. It's probably badly in need of a stage 0, seeing as how I'm getting a good 15mpg highway and a little worse in town. I know we blew the dipstick seal not too long ago and we also ended up replacing the valve cover gasket, to fix an ugly oil leak.
Not sure how relevant all that is, but I'm not too familiar with newer cars. My last car was an old '82 VW Cabrio with a GTI Tranny and a '79 scirocco motor in it, so fixing stuff was as easy as replacing a vacuum line that was at most 1 foot long.
As for OBD codes, I get some obscure ones, but it seems like we get different codes every time we try to use the light thing. Is it possible to get those codes pulled for me, or is reading the light blinks the only way?
Alsooooo, I'll try and get a picture of my motor area out there, if it gives any help.

 

that sounds like the EGR vacuum booster. one vacuum line goes to manifold vacuum, and should be sucking when the engine is idling. the other vacuum line controls the EGR valve, which is tucked next to the block under the intake manifold. When the ECU tells the vacuum booster, it sucks on the EGR control hose, which opens the EGR. There's an OBD test mode that will clatter the vacuum booster so you can see if its working.

here's the EGR system. the vacuum booster[1] is shown at the bottom left, the EGR valve is #8...

 

After tweeking this hose and that hose with very little improvement, I took a Saturday afternoon and replaced EVERY vacuum hose under the hood of my 760T, including the larger brake booster hose and iac hoses. Hell, I even replaced the washer fluid hoses since I had extra hose. It is important to point out that the nipples on the intake manifold can and will get clogged up w/ crud so you may need to ream them out. Compounding the issue is the existing vac hoses may not leak under vacuum but do leak under boost. As has been mentioned, your issues sound very much like vac issues...replace the hoses and be sure to re-install the hose clamps.

 

The cruise control has a vacuum switch on the brake pedal, right next to the stop light switch. The hose to it very frequently rubs through on components under the dash or simply pulls off the vacuum switch.
The cruise control will not function at all if it sees this switch as open, which it will if there is a vacuum leak in the line to the switch. The cruise control will also not work with no vacuum, which may seem obvious, but even the electrics won't initiate if the system doesn't see vacuum.
This line is independent of the vacuum supply lines to the climate control system. However, the fact you have no climate control suggests strongly that the vacuum pump may not be functioning. This pump lives near the throttle body, on the strut tower. I've seen the electrical plug for these disconnected more than once for some reason.

 

It seems like everything is plugged in, but I think there's a tube missing off the vacuum pump. The EGR booster isn't sucking at all, either. Not quite positive about all this and our Chilton manual seems to favor tiny pictures that show nothing of the engine or vacuum lines, etc. I'll definitely try getting all of my lines replaced sooner or later. I'll get a quick picture up too, hopefully.

 

see my diagram. hose 4 should be sucking when the engine is idling. if its not, clear the orifice tube off the intake manifold with a bit of wire or whatever, and replace it with a fresh vacuum line. every b230ft i've seen has had generic euro metric vacuum line, both ends held on with the sorts of clamps you use a small pair of pliers to release, and the tubing secured as convenient with black tie wraps..

if hose 4 is sucking, turn the ignition off, OBD jumper in #6, ignition on (II but not starting engine), put the ODB thing in diagnostic test mode 3 (3 1 second presses of the button about 1.5 seconds apart), and the EGR vacuum controller shoudl be going click-clack-click-clack-click-clack til you turn the ignition off. connect a short piece of hose to the lower vacuum line (#6 on that picture), with #4 hose disconnected, and blow gently into your short hose, and you should feel the pulses as the vacuum booster thing goes on/off/on/off.

but, I really don't think your EGR system is causing your symptoms, however if enough of your vacuum hoses are leaky, all sorts of things go sideways.

 

Actually, hose six is sucking? I'm not sure if that's good or what, but that was the one sucking. The EGR OBD test worked well, and I could feel the pulses, etc., but hose 4 produces no suction or anything and hose 6 was the only one sucking. I tried reversing these hoses on the EGR pump, but then I get a really ugly idle if I rev it high. Like, when the hoses are reversed, after a quick stomp on the gas pedal, the RPMs shoot down to 200 or 300 then climb back to 500 and then it just idles ugly between 400 and 700ish.
Also, where the T is on the vacuum pump, is there supposed to be a thing with no hose connected? I'm just a little lost, sorry! I also have a few pictures I'll get up.

First picture is my vacuum pump I believe. We plugged one of the holes up for now, because we weren't sure if it was good to have one of those open. My dad also thought it might do something if he moved the T to the other hole, but either way I haven't noticed much of a difference.

Not positive if the second photo has any relevance, but I'm not sure what that does at all.

Third and Fourth pictures show where hose four leads to in my engine. I don't have a clue if that's where the hose should even go to, but that's where it goes. I tried to clean out the hole where the hose connects to, but nothing came out of it. It also produces no vacuum that I noticed at idle. But again, hose 6 (or what I think is that?) produces the suction.





Also, looking at that diagram, I'm starting to think on the EGR booster that hose 4 and 6 probably are backwards. I'll try and reverse them and see how the car drives, despite the cruddy idle.




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ALSO! Didn't wanna double post, but I just went through and pulled some codes. I've had the check engine light on ever since I got the car, but I'm still somewhat lost as to what to do with these and etc., but I did get some codes pulled:

A2 gave me 1-2-1
A3 gave me 1-1-1
A6 gave me 4-1-3
B5: 1-1-1
B2: 1-2-2