1996 850 2.5 20V - Warm re-start issues after short trip in cold/damp weather Topic is solved

[matomorizo]

Hi everyone,

I’m dealing with a very frustrating issue on my 1996 Volvo 850 (2.5L 20V, B5254S) and could really use some expert advice (Volvo garage could not help, no failure codes).

The Problem:
- Cold start: Starts right up without any issues, especially in cold/damp weather.
- The scenario: I drive a very short trip (~5 minutes to drop off my kid at kindergarten) and shut the engine off. When I try to restart it shortly after, it cranks unusually/struggles to start—sounds like rich/lean mixture issues or misfires.
- The recovery: If the battery holds out, it eventually catches after several attempts. It idles very roughly for a few seconds as if it's about to drown/stall, but after feathering the gas pedal a bit, it settles down completely.
- Rest of the day: For the rest of the day, even with multiple stops, it starts and drives completely normally.
No check engine light or codes stored. The shop couldn't replicate it because it only happens under these specific conditions.

Parts already checked/replaced:
- Crankshaft position sensor
- Camshaft position sensor
- Ignition coil & main ignition cable
- Fuel pump relay
- Idle Air Control (IAC) valve

Next steps / Questions for the forum:
- Coolant Temperature Sensor (ECT): Could a failing ECT sensor report wrong temperatures on a lukewarm engine and flood/starve the engine on restart?
- SAS (Secondary Air System): Could a leaking SAS vacuum hose/elbow or sticking SAS valve cause a massive vacuum leak / wrong mixture on a warm restart?
- Oxygen Sensor (O2) or anything else? Can an O2 sensor cause such a strictly temporary start-up issue?

Given that this issue is so specific to damp weather and a 5-minute lukewarm restart, I'm leaning towards vacuum leaks (SAS) or sensor misreadings. However, no obvious leakages found yet.

I would really appreciate any insights, similar experiences, or pointers.
Attached you also find a short video - this is what it sounds like when finally the car starts.

Thanks in advance!

IMG_3191.mov

(7.16 MiB) Downloaded 9 times

[misha]

Ect sensor or it's wiring from both sides...sensor side & wiring loom side.
Original Ect sensor rarely fail...but wiring oxidise and insulation from wiring loom side tends to brake.
I owned a '97 850 2.5 20v for 26 years and never had a problem with ect...but had a problem with oxidised connector.
Once cleaned and sprayed with wd40 and never had any problem afterwards.

Other than that....spark plugs,cap & rotor,spark plug cables and Maf sensor could be the culprits.

Maf sensor connector is also prone to failure.

Fuel pump relay could also make problems,especially if it is aftermarket.

Sas would give you other problems...it can't stop the engine from starting.

[matomorizo]

Thank you so much for the hints, Misha! I will check and let you know...

[scot850]

As Misha says. In particular if you don't know when the distributor cap and rotor arm were last replaced change those. Only time I had this issue was a 245 Volvo with a worn cap and rotor arm. It started and ran great, except when it was damp it would struggle to start. Changing just those parts returned starting to normal in all weathers (car had had 10 careless owners prior to me with none or little servicing).

Good Luck!

Neil.

[matomorizo]

Thank you, Neil! Will check it

[matomorizo]

Found a little crack at the outer cap - maybe that's it. Will replace it and keep you informed. It was underneath so I could not see it before.

[misha]

Black cover is just a cover...nothing else.
Remove it and inspect a cap & rotor.

[hausmeister]

I had exactly the same issues on my s70 2.0
Was ignition, a bad distributor cap (although recently replaced) was the cause.

[matomorizo]

Hi guys,
Thank you for your help and all the helpful comments.
I changed the distributor cap and cables and the problem seems to be gone for now - fingers crossed!
Best,
Manuel