1996 850 GLT - stalling, sluggish and rough idle

850corb · Post by **850corb** » 19 Mar 2015, 15:30

Hi,

I have a 96 850 GLT Wagon thats been having some issues recently. Usually it starts and runs fine, accelerates and idles smoothly. Recently though I have had the following happen - 3 weeks ago it as I was coming to a stop the revs died and surged and then it cut out and I was unable to start it again.

I thought that this had been caused by a faulty thermostat as it had not been getting up to its usual "3 o'clock" operating temperature. So I had that replaced, and it ran fine for a week at normal operating temps. The same thing happened again - surging when idling and slow to respond when accelerating. It died and couldn't be started again immediately. I was able to start it again later that evening though and it ran fine again.

Drove it for another week without any issues (~200 miles) and then the same thing happened again today (just realized these have all happened on Thursdays...) - surging when idling and slow to respond when accelerating. It didn't die however and I was able to plug my laptop in and get some readings!

This is what the OBD2 output looked like while it was idling roughly:

: Screen grab when idling roughly

From online searches I figure it could be one of several things:
ECT
MAF
Vacuum leaks
Fuel supply

The coolant temp range seems to be OK, I was monitoring it the past week and its always been between 90C and 100C, which probably seems right.

The MAF readings while it was idling poorly seem quite high, usually this is around 4. Unplugging it caused the car to idle smoothly.

Haven't checked vacuum leaks yet, but I presume I can do this by checking the connections and then spraying around the manifold with something like brake cleaner (any recommendations?) and checking for engine response.

Fuel supply - never had to check this before so I would appreciate any suggestions if anyone thinks it could be an option.

Once I turned the car off and reattached the MAF sensor it ran smoothly again. This is what the output looks like:

: smooth idle screengrab

Sorry for the long post, but I figured more info the better. I would appreciate any suggestions you guys might have for diagnosing/fixing.

Thanks very much!

Post by **erikv11** » 19 Mar 2015, 17:12

Three things point to the MAF:

- very negative LTFT
- the comment about unplugging it
- the low MAF reading

Bad MAF can be very erratic. How old is the MAF? Is it Bosch?

Also I would make sure the IAC is clean.

850corb · Post by **850corb** » 19 Mar 2015, 19:51

Ok, thanks. Also just realized I have those screenshots labelled incorrectly, they should be reversed.

MAF is at least 4 years old, so probably much older. I'm. Not sure what make, presumably I should replace it with a Bosch model and not the rebuilt one advance is selling?

IAC is the idle air control valve? I haven't cleaned that since I bought it 4 years ago so I'll do that this weekend.

This might be related somehow, but I did notice there appeared to be some coolant (or other liquid) residue in the airbox and in the hose from airbox to engine. Any idea how that would have got there and if that could somehow have caused this problem?

sacricide · Post by **sacricide** » 19 Mar 2015, 21:04

I've seen many volvos with idle issues and slight misfires without any MAF codes because it's intermittent.

Don't buy a rebuilt one they are trash and I've read many stories of them being bad. Get a used one if your so inclined. It's usually 40 bucks (even though it may not last you long least it's cheap enough to gamble on) and good way to test it.

Or go brand new Bosch if your certain

SUPERBRIK · Post by **SUPERBRIK** » 19 Mar 2015, 21:59

Have you tried the fuel relay? Can be an intermittent issue that stops your engine and gives you a light show on the dash.

SUPERBRIK · Post by **SUPERBRIK** » 19 Mar 2015, 22:17

...either that, or, get a car that likes Thursdays. I think a few Saab models and maybe an early Abarth (but, only after 11:30am CST) actually like Thursdays.

draser · Post by **draser** » 20 Mar 2015, 05:37

Your double digit negative LTFT indicate ecu pulling fuel, so it's running rich. Since temp is correct ECT is working, also o2 sensor is switching. That said other causes are fuel pressure, leaky injectors. Thermostat was a good guess, did you use OEM? At some point you had a code as seen in first scan. Did you check skinny airline coming from pcv return/intake into throttle?

850corb · Post by **850corb** » 20 Mar 2015, 08:29

Cool, thanks! - i've got some things to check this weekend. The code its showing is a P0455 (i think) - Large EVAP leak, but its been showing that for about 4 years without any issues (I have tried to fix it...).

I'm going to replace the MAF, I figure thats a good place to start. Is there a way to check the fuel pressure and fuel relay?

Whereabouts is the PCV return/intake?

and yes I did use an OEM thermostat.

Post by **erikv11** » 20 Mar 2015, 09:56

draser is referring to the vacuum line called "number 3" in this link, it is a very common problem, but check them all.

https://www.matthewsvolvosite.com/forums ... =1&t=65002

Note that checking vacuum lines is a lot cheaper than replacing the MAF but if the MAF is not Bosch then there is a high probability it is the problem.

draser · Post by **draser** » 20 Mar 2015, 14:53

Hey Erik, what's your source for those red vac hoses, and are they silicone?