1995 850 Idle stumbles and wants to stall, couple codes

marklawder · Post by **marklawder** » 03 Sep 2013, 19:59

Hi all,

I've got an issue with my 95 850 non-turbo. When idling or coming to a stop, it feels like it wants to die, the engine speed drops down to ~500rpm, then it surges to compensate for it. I have had code P0172 for about 6 months now, which I think points towards a vacuum leak, but it wasn't causing a problem so I didn't try to hard to fix it. Recently I got a P0103 for an intake leak and found the tube from the filter/maf to throttle body was cracked so I repaired that.

I also re-gapped the spark plugs to .028", they were all about .035" when I checked them. I just put them in at 150k miles, now at 161k, so I would think they are still ok. I also cleaned the intake tube, filter, and throttle body. The stumbling continues. Not sure if it's related, but I have noticed my coolant temp gauge occasionally drop down, then come back up to temp. My scangauge says the temp is steady, so I am wondering if it is a short or maybe a bad coolant temp sensor issue. Doesn't bother me unless there is some connection to this other problem.

Here is a video of it from tonight, see times 0:05-0:25 and 1:23-2:10 for the issue (worst drop at 2:04). Would appreciate any help in tracking this down. I'm trying not to dump money into fixing parts that aren't bad, but from what I've been reading this might be tough to pinpoint. Car was in park the whole time, didn't touch brake or accelerator.

Thanks!
Mark

Post by **jblackburn** » 04 Sep 2013, 08:46

Double-check the connection on the coolant temp sensor - sometimes they get corroded.

The coolant temp will dictate how much fuel is injected.

However, your idle dip when slowing to a stop usually means a large vacuum leak somewhere in my experience.

marklawder · Post by **marklawder** » 04 Sep 2013, 20:27

Thanks for the reply. I forgot to mention that I replaced the ECT sensor around maybe 140k miles along with the thermostat. I checked it again and it looks fine, but I cleaned it and the electrical connections just to be sure. I also unplugged it and tried running; the result was no different other than the radiator fan constantly being on, which makes me think the ECT sensor is OK, since it reacted to it being unplugged.

What I found strange was that when I had it unplugged, the dash temp slowly rose as the car idled. Is there another sensor that feeds the dash gauge? Which one goes to the ECU to control fuel injection? Should I be going after that one instead?

Thanks much,
Mark

Post by **jpr0204** » 05 Sep 2013, 09:11

No sir, that coolant temp sensor performs double duty. It controls the EFI...AS WELL... as the temp. gauage. If your gauge started rising with the sensor disconnected I would say it is becuase the circuit is not being completed.

As far as your idle dipping down to around 500 RPM's and your P0172 code (which if I recall correctly would be "Fuel System too Rich") which means it's getting getting more fuel than it's supposed to. The first thing other than ECT I would look at would be your MAF sensor as well checking for other vacuum leaks. I was experiencing similar issues my 00' Cross Country and it turned out to be a bad MAF. Yes, there could be other culprits as well though.

- Joe

Post by **jblackburn** » 05 Sep 2013, 09:17

Yeah...now that I can see that video...that looks like a MAF or dirty idle control valve.

Does the temp gauge fluctuate as the idle dips?

Post by **jblackburn** » 05 Sep 2013, 09:19

Also...interesting dash for an 850. I've never seen one like that.

marklawder · Post by **marklawder** » 07 Sep 2013, 17:33

Thanks for the help guys, sounds like I need to replace the MAF sensor first and see if that does it. Kinda pricy but nothing else I've done so far has helped. I've tried cleaning the sensor and the idle control valve, but no dice. Will see if I can find one of these cheap locally, not a big fan of the aftermarket sensors though.

Also did not know my dash was special, its broken loose from the retaining tabs and rattles like a snake, so it's got that in common with the others at least.

Post by **jblackburn** » 07 Sep 2013, 17:41

marklawder wrote:Thanks for the help guys, sounds like I need to replace the MAF sensor first and see if that does it. Kinda pricy but nothing else I've done so far has helped. I've tried cleaning the sensor and the idle control valve, but no dice. Will see if I can find one of these cheap locally, not a big fan of the aftermarket sensors though.

Also did not know my dash was special, its broken loose from the retaining tabs and rattles like a snake, so it's got that in common with the others at least.

Get your hands on a used OEM one. Should be able to get one for cheap!

marklawder · Post by **marklawder** » 07 Sep 2013, 18:12

Found 3 850s at the local yard. A 93, 96, and a 97. Not sure if you can test these off the car, but it's an easy part to get to so I'll see if they let me plug em in to mine and test before I take one. I'll update here if this fixes the issue in case someone comes upon this thread with the same issue.

marklawder · Post by **marklawder** » 28 Sep 2013, 16:56

So I never did replace the MAF, for some reason (cost and effort of getting one probably) I never got around to it. I did replace the ECT sensor and the broken intake hose I found which did not help. Never could find a vacuum leak and I looked a lot for one. I went after oxygen sensors and unplugged them one by one and voila! One of them unplugged has fixed the issue! It's running smooth now, just rich. Got some smoke coming out of the tailpipe when I gun it, but at least the problem is found. Now just need to replace that sensor.