94 Volvo 850 shudders, idles real low, stalls, and accelerates slowly

Question

I have a 1994 Volvo 850 wagon with 120,000 miles, a non-turbo engine and an auto transmission. A week ago, my flashing arrow light came on (it does this about every other month). I cleaned the PNP switch which was the apparent culprit, and the car drove just fine

About 3 days ago, I noticed it stalled out on me and idled at about 600 rpm...about 300 less than what it normally does.

Today, I start the car up for work, and it idles anywhere from 900 rpm to 400 rpm and stalls almost everytime I stop. When it does idle, it sounds like a quieter version of a Harley Davidson motorcycle! It will start back up every time, but it will continue running very rough. When I accelerate, I need to floor it to get any pickup (it drives slower now with full throttle than half throttle when it wasn't messed up.) after about 10 seconds of flooring it, it gets going and drives OK until I need to slow down. It tends to act a little better once it has warmed up a bit but it still acts up a lot.

What would you think is the problem? I don't know if its a fuel line problem, an air problem, or an idle problem (or none of the three!)

Thanks,

Joe

Answer 1

test don't guess. first thing to do is retrieve any and all codes. the 94 850 has  diagnostic box[s] at the right front of the engine compartment, you want box "A"  terminals 2 and 6 [2 is fuel 6 is ignition] insert pigtail lead into socket and push button [key on position, engine off] for about a second then release the red light emmiting diode will flash a 3 didgit code, after each code push button again until first code repeats [record all codes as you get them in 2 columns one for fuel codes and one for ignition codes.

[in north america the haynes manual for this car is readely available and worth purchasing].  it has the code tables to decipher your faults or you can ask here, however,  i am suspecting by your discription, that the root fault will be found to be the coolant tempature sensor [failure here can cause many subsequent fault codes to be stored] [this sensor is located below the thermostat/ water outlet housing]

tip: when purchasing sensor get a new thermostat and seal at the same time [get these parts from volvo, other sources have been found to be lacking in quality] and do the job with the engine stone cold to eleminate the possibility of scalds then clear the codes in both sections either with the diagnostic socket or disconnecting battery ground cable

with no recorded faults check fuel pressure with a known accurate gauge [the test port is on fuel injection feed rail just behind the throttle body the spec is approx 35-43 psi[ if i remember right] if too high suspect pressure regulator, if low or close to normal

but drops rapidley when engine is cut off. suspect possible injector leak into manifold or leaking through the pressure regulator vacume port [remove hose and inspect for fuel drainage while running] [NO SMOKEING OR UNSHIELDED LAMPS WHILE WORKING ON FUEL SYSTEMS]

PREFORM THESE TESTS OUTSIDE OF ANY BUILDINGS AND KEEP A CLASS "ABC"EXTINGUISHER HANDY

if at this point all shows up as normal try unplugging  the mass air flow meter and preform a short road test away from heavy traffic [if car actually performs better, it is a clear indication that the mass sensor has failed][upon return check socket #2 again to see if computer recorded a mass air flow code [off top of head i think 121 should be recorded] if not recorded start to suspect the engine computer [these rarly fail on volvos-- i think i may have had to replace 2 in the last 28 yrs]

note: the three most common over fueling faults are caused by bad coolant temp sensor[yours may still be working but out of range, thus no code] bad pressure regulator[not directly monitered by computer systems], and [rarely] air measurement device.

i hope these words shed light on your ill's good luck

Answer 2

If the vehicle shakes a bit when its running roughly and sounding like a Harley, then that sounds like you may need some ignition coils, or a new set of spark plugs.  You will also want to check out the MAF (mass air flow) sensor and the MAP (manifold absolute pressure) sensor.  The MAF will be on the air duct from the air filter box to the throttle.  It will be on the air filter box itself.  Look for a vacuum hose from the manifold, there should be one that goes to the MAP.  I can't remember where it is on the 850's, on the S60 it is front and center of the car, bolted to the underside of the header panel above the radiator, you can check there to start.  Start with the coils/plugs and go from there.  The next time the flashing arrow (transmission warning light) comes on, take it to your local Volvo dealer and have them look up the code for it.  The rough running doesn't sound like a fuel problem, because your car would likely die when you give it throttle, it sounds more like a spark issue, or possibly MAP/MAF sensors.  (Do MAF before MAP)  Lastly, check your air filter and make sure it is nor dirty or (in rare cases) wet.  Hope this helps.

Answer 3

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