OK been having some issues with my 850. Haven't experienced this before. I thought it was my tranny as I first had it happen while on a road trip, but I'm thinking it is engine related.

Recap:

Driving on 180 mile trip, 50 miles in the car "bucks" once going up a hill. Did it again 10 miles later. Pulled over saw some foam on the tranny dipstick and thought it was the tranny. Added fluid. Still did it.

Car sat overnight. Drove back home, did the bucking again about 50 miles in and did it again every 10 minutes or so. Again thought the tranny was giving up the ghost. At the end of the trip, about .5 miles from my house the CEL flashed as well as the ABS light, a bunch of codes were pulled, the most notable was the MAF sensor absent (1-2-1). In addition I believe the ECT was thrown as well. But also a bunch of ABS codes and instrument codes (#7). But I recently replaced the ECT with an OEM one so I'm not sure why that is there.

I cleared the codes and none have since come back.

However, the bucking is getting more frequent. Over the past few days the car will start than immediately stall, although it doesn't always happen. Now sitting in my garage it will try to die on me as it idles. If I give it gas and hold it at say 2000 RPM it will slowly bounce down and hover at 1500 RPM and then bounce around, it's not steady. It's not related to highway speed any more (as it was doing it on my original road trip) it will do it at any speed. Coming home today sitting on a side street the car just died while sitting in traffic.

I've cleaned the MAF and IACV contacts. Neither helped. I pulled the MAF sensor connector out, it idles kinda crappy and once given gas from idle it shakes a bit but once up at RPM speed it runs good. It doesn't die with the MAF unplugged. Not sure where to go from here. Any ideas?

-matt

 

Hello Wheelsup,

A shot in the dark here. Might it be the fuel filter?

The reason that I ask is just after I got The Anvil I was sitting in the lot at work on break and was noticing the klm-to-go on thetrip computerand thought that it would count down like most that I have seen by 1 klm/mile until zero. To my surprise it drops by 10klm and not 1klm and the car ran out of gas seconds after it reached zero.

For the next couple of weeks the car would stall out, buck and chug and I was really afraid to go any where. The bucking and chugging I attributed to the face that I had run the system dry and that there was air in the line so that when the car was running and one of the air pockets got pumped into the engine it would cause the misfire/bucking/chugging.

A plugged or dirty fuel filter can cause the same type of issue in that it may be starving the engine of fuel by not being able to flow as much as is needed.

Hoping this will help.

Happy New Year and [sm=icon_cheers.gif]

 

Hmm that is possible I had a similar issue awhile ago that was indeed the filter but it didn't do what it is doing now, that is buck while on the highway. It would just not start. It starts fine but then dies shortly afterward. Also it would die while rolling up to stop lights where as this seems like a random failure.

I'm thinking I should replace the dist cap/rotor, fuel filter, those are pretty cheap. Also I was thinking about driving with the MAF unplugged to see if it bucks then. But what I don't want to do is start throwing parts at the thing.

 

If the MAF is bad it will run better with it unplugged then plugged in. When unplugged the car goes into a limp home mode.

 

FYR.

Also keep an eye on the coolant level & unusual colour in the reservoir. The foaming on the tranny dipstick concerns me.


JPN

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I had a similar issue with our 850 and it turned out to be a bad coolant temperature sensor. If you are concerned about the transmission, I suggest this: Let the car cool off overnight, and check all the fluids cold in the morning. Make a note of the transmission fluid level and color. Then start the car and drive it for about 5 miles. Then put it in park and shift it through all the gears, pausing about 3-5 sec in each gear, then put it in park again and with the motor idling, check the transmission fluid level

 

OK update. I cleaned the MAF today with MAF cleaner. Cleaned the CPS with electrical contact cleaner (just to make sure). Car runs better with MAF unplugged, it will now die completely if I plug it in. It runs OK with it unplugged but still drops in idle every few minutes like it is going to die, but doesn't. I'm trying to find an 850 around here that I can swap out my MAF to see if that fixes it. I don't want to buy another one right now because I have a feeling it won't fix it - because the car still bounces around every few minutes even with the MAF unplugged. If it didn't do this I would say I was out of the woods but it just doesn't seem right. It idles fine most of the time then BAM bucks/quits depending on speed.

Also I got another CEL today, just before the car died, another 1-2-1 from A2 which is the MAF sensor.

This might be a case for my mechanic next week, we'll see if I can scrounge up a MAF somewhere to swap. I'll know for sure that way, and can at least point him in the right direction.

The foam is weird on the tranny and the coolant level goes down ever so slightly but I drove 300+ miles and it dropped about 1/2 cup, I think it is leaking from somewhere but it is such a slow leak that I don't think it is the headgasket or leaking into the tranny itself. It started doing that after I replaced all my coolant hoses. That is a separate problem right now (the tranny foam). Also it doesn't always foam it did on that road trip but after driving several times now I see very small bubbles sometimes but no actual foam.
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Sounds like a plan, let us know the updates when they come along.

It maynot hurtto have the cooling system pressure tested. I believe the money would be a well-spent one.


JPN

 

Sounds like Air idle control motor is dirty, have you cleaned the flame? What about the common vaccume leak right by the throttle body ?Throttle body cleaned recently? Could be a bad throttle position sensor, that would mess up your shifting.

 

Ok put a new (used) MAF on there from eBay and it seems to have fixed the problems, especially the idling one. Driving tomorrow to work and back will tell me if it's stopped the cutting out or not. Out of curiosity does anyone know if the MAF sensor has the authority to tell the injectors to stop fuel flow? I'm wondering if this is what was going on. It really feels electrical or fuel related and that's the only thing I can think of that the MAF would have an impact on.

-matt

 

I do not believe the MAF sensor has the authority to stop fuel supply. In general, MAF sensor tells the ECU how much air is passing through the induction system and the ECU decides how much fuel matches the amount of air being supplied (as well as other parameters being considered).

I believe the vehicle speed sensor does have the authority to cut fuel supply. Tech would be able to give you more accurate info than I possibly could.


JPN

 

I would think so I know it can tell the computer to make them stay open almost all the time and flood the car out. So I would think it could work the other way as well.