Code 315 and low idle at start.
 

Getting code 315 for a while now, so time to get at it...My gas sending unit (gas gauge sender is dead) and will replace that next week, but I dont know if it could be causing my 315 code. One side note, sometimes after filling up the gas tank, the car stumbles for a bit when starting it up at the gas pump, and also has similar symptoms in the summer on hot days when the car sits in the parking lot while im at work. It stumbles on first start up for a few seconds then runs fine. Seems to me like all this is related. Any info on any of this would be great. I dont just wanna start throwing parts at it until Im sure what the problem is.

The stumbling would be caused by one of two things. A bad Fuel Pressure Regulator or a Bad Fuel Pump. I would start by taking a closer look at the FPR.

Thanks FCP....Ive just read another post that it might be the evap valve...now last year when I did some work on the car, I broke a plastic connecter on some valve located by the right side of the rad...just under the air intake tube...I glued it back on with a good compound, but winters are cold up here....if that was the evap valve..and had a small leak,,,could that not cause this start problem and code everytime I fill up?...or it could be the pump,,,I put in a used pump last spring...whole assembly....so it might be that too...but as you are FCP...you can tell me if I only need to buy the motor kit and not the whole pump that you sell online.

From here:
https://volvoforums.com/forum/volvo-850-16/list-diagnostic-trouble-codes-dtc-9856/

3-1-5 EVAP emission control system fault

Yes, you could have a broken evap valve and, yes, that could cause those symptoms.

If you suspect the fuel pump or fuel pressure relay, suggest you get a fuel pressure gauge and ck it.

Also if you do have a bad fuel pump, then yes, you can replace just the pump (assuming your plastic housing is not cracked or broken).

If the EVAP Purge Valve (which you are alluding to) is physically broken, this can cause misfire.

What i was "alluding to" was that he has an evap fault and that if the canister purge valve is stuck open, have seen this cause rough running at startup like he described. As it says below, purge valve should only be open when engine is running above idle.

What i was also suggesting was that he ck the fuel pressure before replacing the fuel pump and/or pressure regulator. I like to diagnose the problem before throwing parts at it...

From volvo manual:
================================================== =====
FUEL EVAPORATIVE SYSTEM (EVAP)
Evaporative emissions system is designed to prevent fuel
vapor from entering atmosphere. Fuel system is completely sealed and
vented only through a carbon canister. System consists of
pressure/vacuum relief fuel filler cap, rollover valve, charcoal
canister, purge valve and various connecting hoses.
Fuel pressure/vacuum relief filler cap allows excessive tank
pressure to vent. It also allows air into fuel tank if vacuum should
become excessive due to a malfunction in fuel evaporation system. Fuel
tank vapor is vented by a line through rollover valve to charcoal
canister. Rollover valve is located in vent line close to fuel tank.
Valve is designed to prevent fuel spillage if vehicle rolls over.
Valve is open until vehicle is at a 45-degree angle or more from
horizontal position.

Canister Purge Valve
Charcoal canister is filled with activated charcoal. Fuel
vapor from tank is absorbed by charcoal when engine is not running.
When engine is running faster than idle, canister purge valve opens
and fuel vapor is drawn into engine and burned.
================================================== ===

gdog: My message was intended for the guy having the problem, not you!

Sorry Henry; i misunderstood your post.. :o