99 S70 GLT Engine B5254T [Vacuum leaks, hoses, Snorkel] Topic is solved

Post by **Grantkat** » 08 Jan 2025, 11:32

I have a very recent issue on starting. When i start the car fires right up however instantly wants to stall. If i dont give it gas it stalls immediately (cause for me recent lawnmower syndrome). However if i stay on the gas for about 1 min (sometimes less) it will idle normally and run fine. once warmed up it will be fine to restart.

I have done some research on here and have seen coolant sensor, MAF and fuel relay however the descriptions of their symptoms arent quite like mine.

likely cause and advice please?

Post by **Chuck W** » 08 Jan 2025, 12:24

No codes?

I'd start with coolant sensor and/or the FP relay if the issue started when it got colder.

Post by **Grantkat** » 08 Jan 2025, 15:50

HI Chuck NO CEL light no codes.

New development - tonight after coming home from work (40 minute drive at mostly 60 MPH +) I stopped at the store (10-15 minutes stop). When i came back out and started the car again it seemed to want to stall but then after a few gentle revs it was fine. before exiting the parking lot, the RPM dropped from 1100ish to 600ish and the car started "chugging". here is my best description of what followed. for about 100 yards when i push on the accelerator it would barely go followed by a "chugging" where it would move forward somewhat then back to giving gas and it barely moving. The engine was making a "dieseling" sound. I was working the pedal up and down and it was sort of chugging and lurching somewhat as if sometimes the pedal was working and others it wasnt. Then all the sudden the engine kicked into normal operation, the car jumped, sped off and I took off down the road like nothing happened. Upon getting home there was a hint of that sort of rich dieseling smell from the exhaust after turing the car off

Post by **Grantkat** » 08 Jan 2025, 15:51

again - no codes

Post by **Chuck W** » 08 Jan 2025, 16:38

The stumble to all of a sudden running fine leads me to think it could be a fuel delivery issue. (How old is the pump?)
How much gas is in the tank? I would check fuel pressure as well.

I had a car that would do the random stumbles and then clear up. They issue was a shoddy FP replacement by a PO and the feed hose out of the pump inside the tank was barely hanging on. (See PIC).
The fuel pressure would randomly drop due to the open connection, and cause it to run poorly. It was obviously less of a problem the more fuel that was in the tank.

The relays tend to be more of a hard start when cold (at least in my experience) and not so much of a running like crap. They're always a possibility though.

Post by **Grantkat** » 08 Jan 2025, 17:00

Fuel - tank nearly full.
Pump - unknown fuel pump is a PO and purchased as is about 18 months ago.
I will test the relay and see what gives.

whats a good way to test fuel pressure? there is a Schrader valve at the end of the fuel rail

Post by **Chuck W** » 08 Jan 2025, 17:10

That Schrader is the location to test.

Post by **erikv11** » 08 Jan 2025, 20:48

You can use a cheap-o tire pressure gauge on that Schrader valve. The gas will ruin the gauge but give a reliable, approximate reading. Or spring for a proper fuel pressure gauge setup.

Post by **Grantkat** » 09 Jan 2025, 05:38

I will rent a fuel gauge set up and test the fuel pressure.

Another question - any idea about why the engine was chugging and "dieseling". That seems beyond a fuel delivery issue?

Caesium · Post by **Caesium** » 09 Jan 2025, 08:05

As you mentioned the throttle pedal not being responsive during one of the times it was acting up, I'd get a sweep test done of the electronic throttle body if that hasn't already been serviced or replaced with an updated unit.