Unresponsive; random sputtering
 

Hello all,
I recently got a '95 850 (Non-Turbo, 2.4L) with some issues. When I got it, it was throwing the MAF code (P0103) and idling very poorly, so I replaced the MAF sensor which fixed the idle.

I also replaced the oil, oil filter, and air filter as a precautionary measure.

After replacing the MAF sensor, I cleared the code and it didn't come back, and when test driving in sport it went very well for about 0.5 miles. It would then become very unresponsive to the gas pedal at random, no matter how hard or often I pressed/pumped the pedal the engine just seemed to idle sort of roughly. Then, it would spontaneously resume normal operation for a few minutes, and then become unresponsive again.

I checked the plugs; they were a bit corroded, so I replaced them with NGK Iridium. Also cleaned up battery terminals. Took it for another test ride, and the same issue happens, except this time it throws the following codes: P1310, P0305, P0303, P0300, all relating to misfires. Thing is, when it runs great (like the first part of a test ride in sport) it has full power and feels like it has full compression through all RPMs.

I then replaced the fuel filter; this didn't fix the problem.

Now I'm stuck, thinking maybe its the throttle position sensor or fuel pump, but not sure. Any thoughts?

EDIT:
It doesn't matter if I'm in gear, neutral, or reverse, the throttle is equally unresponsive and I cannot rev the engine or affect the RPMs at all when it is acting up.

Turbo or N/a?

Not turbo

1st, ditch those plugs, has been proven the best plugs for the 850 are the oem bosch ones.
2nd, could be a loose conector for the afm, would also check the fuel pump relay, this is a know issue and so easily fixed.

i might also check the camp and rotor. and also check if you have an air leak where you installed the maf...

Could be the O2 Sensor.

Alright, checked the rotor and cap and they look alright. I am getting no O2 sensor codes, but not ruling it out entirely.

Did a bit of digging, and found that my flame trap looks partly clogged. I tried running idle with the dipstick out, and I can see a barely discernible white steam/smoke coming out (probably wouldn't notice if I wasn't looking for it). Thinking of PCV system replacement, using this guide http://www.lakesidedp.com/uploadpics/pcv/ , but would like to hold off on that unless I'm really certain because its a $155 kit.

Wondering if the flame trap is supposed to have any "internals", right now it looks kinda just like a screen.

yes the flame trap is a honeycomb type thing.

if you are throwing misfire codes maybe do wires? (if you haven't already)

1st - no air leak apparent around the MAF; I also test ran the car with the MAF completely disconnected, and what happens is the idle gets very erratic. Plug it back in and it goes perfectly stable. So I think the connection is probably alright to it as well.

2 - The fuel pump relay; I could replace the caps on that this week if it might help.

3 - As for the wires/misfire, I took it for another ride after it threw the codes initially and I erased them, the same problem came back but it didn't throw the misfire codes. After cleaning the flame trap today I rode it again, same problem, but again no codes. So I'm wondering if it was just the ECU getting used to the new plugs.

So now, I've cleaned the flame trap (as well as I can with a pick/carburetor cleaner/water pressure) and the housing, as well as cleaned inside the throttle body with carburetor cleaner, and the same problem is occurring.

wires or coil....

Looked at the spark plug wires; they say "45 05" and are marked "Volvo". PO had it dealer serviced until about '06 (I have the maintenance manual with stamps), my guess is that the dealer put them in. As far as I can tell, they look to be good condition, OM parts. So that leaves the ignition coil?

i would think so.

has it ALWAYS sputtered? or did this start? might also want to check compression and fuel pressure.

when I got the car, it would sometimes stall out due to the bad MAF, so I was not able to see/diagnose the current sputtering issue.

Strange, just seems to completely disregard any pressure on the gas pedal regardless of gear (neutral, reverse, park, drive) when it does it, and then a few seconds (5-20) later, it will decide to go well for a bit longer.

Have a fuel pressure checker that I'm borrowing and will use that in the next few days (maybe tonight). Maybe compression, although I'm not sure, as when it does run well, it runs GREAT (no misfires and great power).

Pulled the ignition coil out, I don't see any leaks or cracks, is there any way to test it using my multimeter? I suppose I could also clean the terminals and connectors up a bit on this.

not sure. it would be resistance test for sure being a coil. what you could do in a pinch not knowing what the spec is just take out a spark plug and put it on the end of the wire. then lay it on the valve cover, blue spark is good. yellow is bad.

Well, I ended up getting the fuel tester back, so I just cleaned the ignition coil contacts and body (electromotive and contact cleaner, CRC) and put it back in.

Tested fuel pressure, its constant at 40 psi and whenever the pressure is released it returns to that value almost immediately, so I don't think my problem is the fuel pump.

Starting the PCV job, hoping to replace a bunch of vaccuum hoses in the hope that maybe one is leaking and causing the problem.

By the way, I noticed the small hose that comes out of the side of the flame trap body was clogged, so I replaced it with a new vacuum I had around that was about the same size. Since I have some good condition hoses around, can I use some of those in place of the ones in the PCV kit?

Problem SOLVED!
 

So, turns out my issue was the AIRBOX THERMOSTAT. Whenever I would experience sputtering, everything from the airbox to the intake manifold was burning hot; the airbox itself was almost too hot to touch.

So, we looked at the inside valve, and lo and behold the thermostat was completely and utterly shot (had no pressure to push the pin out at all).

Wedged some washers in there, it runs perfect now.

This would also explain why I had to replace the MAF sensor when I got the car, and why I noticed that the sensor was a bit melted -- the hot air fried it!

So, for anyone who has MAF issues or a completely unresponsive engine after the car warms up, just check out the airbox thermostat. It was a 50 cent fix (a couple of washers).

Could you post picture of this?

I don't have pics myself, but the airbox thermostat is a temperature controlled device that has a pin that goes in or out depending on the temperature. This pin pushes a spring, which controls the valve in the airbox to take in either cold outside air, or air that has been heated by passing over the exhaust manifold (ever see that silver tube behind the engine that goes to the airbox? thats the hot air intake for this).

My thermostat was busted so it would never go "out", and the valve was always in the closed/HOT position. Which meant that NO outside air was passing into the airbox and then onto the intake manifold, but only already heated air. Seeing as its over 90F ambient here, that can be a problem.

Wwhat I did is took the pin out of the broken thermostat, put a nail on it instead (a bit longer than the pin), and hung washers along the nail. I then put the modified thermostat back in, and the washers on the nail to push the spring that would push the valve to the "open/COLD" position.

There is a picture of someone holding the valve open with wooden dowels here - (3rd post) - http://www.matthewsvolvosite.com/for...pic.php?t=8830

and there is more info on the airbox thermostat here - https://volvoforums.com/forum/showth...box+thermostat

Hope that helps, if I can get out there and get a photo (have to take the airbox back out to get one, I shoulda done that while I was there lol) but the airbox thermostat looks like this - http://www.fcpgroton.com/product-exe...category_id/10

Also, there are far easier/better ways to defeat the airbox thermostat than what I did; just shoving anything in to compress the spring will work just as effectively.

quick note - this airbox thermostat is NOT on turbo cars from what I understand. It appears to be only on NA cars.

Thanks, this is much better than picture