Volvospeed Forums: Three Fat Tigers - Viewing Profile

The most common possibilities would be either the radio suppression relay (RSR), or it could be a failing ignition module.

The RSR is fairly easy to test, normally there is an identical relay right next to it that is for the radiator electric pusher fan, just swap the relays. You might pop the cover off the relay and look for any cracked or failed solder joints and re-solder them. Otherwise it's a simple single pole single throw relay, any standard generic automotive type relay will work in it's place, although you would want to change the socket to a matching generic socket.

The ignition module is the same part as used on all '89+ 240s, 740s(non regina), 940s(non regina), as well as earlier 740s going back to '85 IINM, so finding a used one shouldn't be a stretch.

Otherwise it may be a failure with the wiring to the distributor, another common failure point. Or a possible fault with the hall sensor in the distributor.

If the backfire is from the intake/engine compartment, odds are you are running too lean due to an intake leak somewhere between the MAF sensor and the clyinder head. If the backfire is from the exhaust (like gun shots), odds are you have some sort of ignition system failure, which could be timing belt related.

You might want to check your timing belt marks.
http://www.threefatt...TimingMarks.htm
Line up the crank to TDC, pull the fan off the water pump, walk the pump pulley forward off the pump, no need to loosen the fan belts. Then pull the top timing belt cover, use a flash light to look down inside the lower cover to verify the crank timing mark.

Well it doesn't sound like anything I've heard of before, not sure how it could rev up & down without diver induced throttle oscillation while in gear and cruising down the highway, though I have seen cruise control do that when there is a cruise related vacuum leak.

Odds are it is some sort of intake leak, or a possible fault related to the IAC, maybe a bad or loose IAC hose. You might also inspect the wiring for the distributor, maybe some sort of a fault with the hall sensor.

You might read through some of these:
http://www.brickboar...nceSymptoms.htm
and see if anything fits your symptoms.

Most likely the muffled pop is a back fire through the intake manifold, an strong indication that it's running too lean, which fits with the other symptoms.
→Look for any kind of intake leak, make sure the boot between the air flow sensor and the throttle is in good order, not loose or out of place
→Check the aux air valve hoses, make sure they are not loose, especially at the intake manifold, use plastic tie straps for hose clamps as needed
→At idle, spray some carb cleaner around the intake manifold gasket and injectors, any change in engine speed would indicate a leak
→Check your ignition timing; make sure the timing belt hasn't jumped a tooth.
→Inspect the brake booster hose, sometimes cracks in this hose can hide from sight yet cause such issues.
→If you have the lambda-sond (O2 sensor), make sure you can hear/feel the frequency valve buzzing while starting or running.
→Otherwise you may want to move on to checking the base fuel mixture and the fuel control pressure.

Also you might explore http://www.kjet.org/
they have a number of factory manuals (green books) available that cover your fuel system.

You might try some Auto-RX for the engine sludge.
http://www.auto-rx.com/
You might look around this forum as well:
http://www.bobistheo...&Board=5&page=1

Oil:
Down here in VA I tend to run 10w40 year round in all my cars, but we've had very mild winters here over the last decade, otherwise in a colder climate I would run 10w30 in the winter. In the past I used only Amsoil synthetic, but now I use only Mobile 1. Almost any oil should be ok for 4-5k miles service. Synthetics may leak more as they often have a lower viscosity when cold, but I would stick to 10w and avoid 0w, 5w and 15w variants. I would not run less than 10w40 in the summer on an engine with high miles.

Filter:
MANN or Volvo (same product), otherwise I'll use Mobile 1 filters, or I'll settle for the Bosch Premium, which is half the price of the M1, and is basically a Purolator PureOne without texture (Bosch owns Purolator, so no surprise there).

Fuel:
Use the lowest octane fuel where you do not hear pinging from the engine, anything higher is normally a waste of money. You might also try playing around with the base ignition timing, bump it up a couple of degrees at a time and see if you can find better power while still avoiding ping.

Rear Axle:
Basically any SAE 90 or 75-80w90 API GL-5 gear oil will work. If you want to go nuts, try Mobil 1 Synthetic Gear Lubricant 75W90.

Manual Transmission:
Type F automatic fluid. I think it's type F because IINM, type F isn't as susceptible to foaming as Dexron. The cheapest brand you can find is likely as good as the most expensive. Otherwise go with Redline Type F, or if you are having any shifting issues, I'd consider switching to Redline MTL.

Owner's manual, if you don't have one:
http://new.volvocars...bo/85240_00.htm