Just bought my second 940 wagon after putting 100k on another over 5 years. Decided it was time to upgrade to turbo. the new one has just 96k However, it wasn't as in good shape as I had hoped for one thing that bothers me is the idle. Its rough and the car shakes slightly. I have already changed spark plugs and cleaned the throttle body and things haven't improved. It almost sounds like its backfiring slightly. its also getting only 20 mpg. What should clean/replace next? What are some things that effect idle. Also what gives a car bad mileage besides oxygen sensors?

 

the mpg is fine, look at you motor mounts

 

Checked the mounts. They dont seem to be cracked or anything. The way the poor idle works is it dips for a moment to 500 or less rpm and then has a mini backfiring sound then pops back up to proper idling speed (750 rpm?) for a moment befor diping again shaking the car. the cycle of dipping and surging back to normal idle speed happends over a period of a second or less.

Where i checked that milage was all on one trip on a freeway. My brother's turbo 940 gets around 24 mpg on freeways. im pretty sure 20 is lower than it should of been.

EDIT: Ok, just changed spark wires and did a 120 mile road trip. Had a canoe on the roof and got 16.2 mpg. Not good. rough idle is better than it was, still has mini backfiring. I also took the distributor cap off and the contacts inside don't seem to be over-worn. I sanded them off a bit for the hell of it.

I can also hear a hiss somewhere around the intake manifold. I poured and sprayed water over pipes and hoses but couldn't locate the exact source of the hissing. Its a turbo, is there supposed to be a hissing noise at all?

 

Found the little sucker!
I listened to my brothers car and his didn't make the same hissing sound that mine did. It had to be an air problem.

I started spraying throttle body cleaner all over the place. i found an area around the 1st injector that would make the motor rev slightly so I took a piece of plastic hose, put one end in my ear and listened through it and found the exact spot. Its the intake manifold gasket on the first cylinder on the right side.

Just for kicks I popped a hose off the throttle body and squirted cleaner inside while the car was running. It stalled. I then took cleaner and squirted it directly on the spot where the hissing came from and I stalled it out again. The thing must be wide open for that much cleaner to be able to get in.

Now to find an intake manifold gasket, replace that and then try to solve the MPG issue.

 

Was just going through all the service records and manuals and stuff. In the back of the manual it claims that the car is actually a 945TG. The markings on he car claim it is a 940. Was it a common thing for Volvo to not put the full designation on it?

Its a fully equipt car. Leather, power, heated seats in good condition, moon roof, turbo, glass headlights, and the engine and interior are beautifully clean. its got everything and more, all working and with only 96k.

It only had 40k put on it over the last 12 years. I wonder how long it has been sitting. I bet a Volvo enthusiast would love this thing. I almost fell not worthy of ownership. thinking of selling it to someone who would take care of it. I need a beater that I can put massive miles onto without breaking.

The only things it needs are a new muffler, new intake manifold gasket and something to solve the low mileage.

 

945TGA, actually. Turbo Gas Auto... They used to have that type of designation...

It sounds like a nice car! In my book, the body and especially the interior are much more important than the engine. The engine is easy on these cars, the other stuff is what is expensive and usually trashed. As far as the MPG, 20 is not great, but not unheard of-you can probably kick it up to 24 or so--tire pressure, alignment, tune up, air filter, that kind of thing...

Or if you really want to sell it, we can talk, where are you?

 

I'm in upstate NY. travel between Rochester and the Syracuse areas for school and whatnot.

 

Replaced the intake manifold gasket today and what a surprise. Someone had already replaced the gasket once already and somehow missed a stud while installing. On calendar 1 the gasket wasn't even close to sealing the intake. I there was probably a 1/4 inch gap straight out to fresh air. Check out the pix of the crush-formed gasket.

In the process of replacing the gasket, I broke a little stem off a t valve that goes into the flame trap I believe. I cant seem to find a place that sells a replacement. any ideas where I could find one? I included a picture of that as well.

PS it idles almost as smooth as silk now.