96 850 Fluctuating idle/stalling (VVIS?)

cheap850 · Post by **cheap850** » 16 Jun 2022, 01:22

Hi all,

You have probably seen plenty of these posts, but so far the solutions I've seen haven't worked for me.

I recently bought an 850 2.5-20V (NA) for cheap. The ABS module was broken, which I fixed by opening it up and reflowing the connectors. The idle issue unfortunately persists: With the MAF connected, it runs fine for about a minute when cold and then keeps revving up and down between 500-1500rpm to eventually stall. At first it wouldnt idle without it unplugged (limp mode) either, until I replaced the IAC. Without the MAF it works fine idle and under load now, I can drive it fine (although it obviously runs way too rich still). I figure it runs too rich with the MAF connected, as when I spray brake cleaner into the intake it stalls immediately.

What I've tried so far:

- Replace IAC (solved part of the problem)
- Swap out MAF (used but Bosch and same part no., could still be bad but small chance)
- Disconnect O2 sensor, runs just as badly (might be a sign? heating element is tested and good, data wires dont have continuity both ways, but not sure if they are supposed to)
- Replaced vacuum lines, made sure they are connected properly
- Disconnect SAS system
- Cleaned PCV system (it was clogged and caused positive pressure, which is solved now)
- Replaced intake gasket (it was leaking & see PCV above)
- Sprayed brake cleaner across vacuum lines and tree, intake to check for leaks (result: no leaks)

What I'd still like to try:
- Disconnect TPS to see if there is any change. I don't hear any 'click' when turning the throttle valve, which I read its supposed to do?
- Jump fuel relay, although I dont suspect this is the issue as the car runs fine in limp mode

I have a CEL, but no codes on the OBD2. I have no experience with OBD1, would I also have that system in place?

Could SAS be the reason it runs better the first minute when the engine is cold (not started for 24h)? I might be able to check this today by disconnecting the vacuum on the SAS valve on the bottom of the intake (I assume that's what its for) before starting the engine. Scrap that, seems I have VVIS, not SAS.

What else can I try before buying a new O2 sensor? I will be with the car again later today to try diagnose it a bit further.

Thanks in advance! I'd love to have this car running properly again, it sounds great.

cheap850 · Post by **cheap850** » 16 Jun 2022, 01:25

ETA: I also replaced the rotor, rotor cap, spark plugs (Volvo OEM) and airfilter. Didnt suspect these anyway since it runs good in limp mode.

I have VIDA 2012D and a DICE, would I be able to diagnose the 850 with that, or is the car too old?

Just reading up on this: viewtopic.php?f=1&t=74352
It seems my 850 is equipped with VVIS, and probably not SAS. I dont seem to have EGR either. Is there more information on how VVIS works and how I can check its proper functioning?

I've attached a picture of the engine bay with the intake manifold out of the way. You can see the VVIS system on the intake on the right.

Post by **abscate** » 16 Jun 2022, 04:35

VVIS on a 1996? We didn’t get that system over here in that year. Could your engine have been swapped?

cheap850 · Post by **cheap850** » 16 Jun 2022, 04:46

abscate wrote: ↑16 Jun 2022, 04:35 VVIS on a 1996? We didn’t get that system over here in that year. Could your engine have been swapped?

I think it's an early 1996 just before they changed it. It's a European car, market was probably a little bit different

Post by **jreed** » 16 Jun 2022, 05:36

If you haven't already had a chance to do this, it would be a good idea to check the engine coolant temperature sensor, wiring and connectors.

cheap850 · Post by **cheap850** » 16 Jun 2022, 05:42

jreed wrote: ↑16 Jun 2022, 05:36 If you haven't already had a chance to do this, it would be a good idea to check the engine coolant temperature sensor, wiring and connectors.

Thanks! I will stick a multimeter on it. I didn't suspect it since my fan is only activated when the engine reaches operating temperature, but it might be good to check anyway.

Post by **jreed** » 16 Jun 2022, 05:49

Good luck and let us know what you find. I'm no expert on engine control systems, but my understanding is that the ECU reads the ECT sensor among others to make adjustments to the amount of fuel injected. Additional info is available here: https://www.volvoclub.org.uk/tech/servi ... ertion.pdf

cheap850 · Post by **cheap850** » 16 Jun 2022, 08:16

ECT is good. I checked my TPS, which seems to be a bit off. It doesnt 'click' (removed from the car), as described by some and it also reads 900-2300ohms, while the Bosch spec sheet specifies it should go from 710 to 1380 (see attached). There's also quite a bit of play/wobble between the turning mechanism and the outer casing. I tried running the engine without the TPS connected, but it made no difference. No idea if that indicates anything.

Can anyone confirm this? I could only find tests with the sensor connected, which isnt very convenient considering the small amount of space.

Should the sensor be 'clicking' in one of the outer positions?

cheap850 · Post by **cheap850** » 16 Jun 2022, 10:31

I think I'll just bite the bullet and buy a new O2 sensor, everything points mostly to that so far. It would make a lot of sense.

Post by **misha** » 16 Jun 2022, 11:40

abscate wrote: ↑16 Jun 2022, 04:35 VVIS on a 1996? We didn’t get that system over here in that year. Could your engine have been swapped?

It seems that engine has been swapped.

No VVIS on a EU market from '96.