Hey, guys.
I've got a '98 S70 with 180k miles under its belt. Check Engine has been on the entire time I've owned the car (roughly two years). I'll throw the codes out and give you the details.

P0138: H02S12 Circuit condition (Heated oxygen sensor Bank 1, Sensor2)
P0141: H02S12 Heater condition (Heated oxygen sensor Bank 1, Sensor2)
P0410: Secondary Air injection system fault
P0453: Fuel tank pressure sensor condition

So, for a while, my fuel filter was spitting out gas. Pushed tubes on either side and it's stopped as of late. That was troubling but when I figured it out I was excited that I could be back on the road driving safely.

Then after driving around for a while, I seem to ALMOST stall out when I stop at a light or stop sign. Because of this, I haven't been driving more than two or three miles a day (to and from work). A few other threads I've been in suggest it's my Fuel Pump Relay. After spending a week finding the damned thing, I plan on buying a replacement soon, though I wanted some other input on the subject.

On an entirely unrelated subject, I've got this terrible white build-up on my dipstick every time I check my oil; looks like I rubbed it through the center of an Oreo. Not sure if this would play a part in the aforementioned problem, but I had figured I would put it out there.

If there happens to be any more information I can give you, which I'm sure there's plenty, I would be more than happy to provide it. Thanks for looking!

 

Does the car run ok cold? does it run the same warm? Does it idle smooth or seem to have full power?

It can be that your air pump is not kicking in. There are check valves, a solenoid valve, an air pump relay and the pump itself. Start by inspecting vacuum tubes and hoses into the solenoid valve, the air pump etc. You should also be able to check the solenoid valve with a multi-meter to see if its getting a signal and if the solenoid is firing to open the valve. What the air pump does is push air during cold starts to improve emissions which can account for the 02 sensor codes...

I'm now wondering if this can also be the cause of your oil froth or if that is due to the suggestion that you drive 2-3 miles to work and the car never fully heats up and gets rid of condensation.

Fuel pump relays are easy to find/replace - they are in the fuse box (see the Owners Manual for position in your year). Seems you do have some issues with fuel pressure which should be checked ( ) - it could be the pump, the relay, the fuel filter or the fuel pressure regulator or even the fuel tank cap being left off for a spin.

If you can test for fuel pressure, you can then decide whether to replace the filter (if its of unknown age) then try the relay (or do this first, its nice to have a spare relay if you don't mind the $50 investment).

If you clear the codes do they reset?

 

It runs just fine cold. I've only noticed a problem if I've been driving for more than an hour or so on the highway.

I'll check the valves and pumps first thing in the morning when I have sunlight on my side.

A buddy of mine suggested it might be condensation on my dipstick, so it would seem that's my main culprit for that issue.

Right now I'm waiting on the Fuel Pump Relay to come in the mail. I feel that may be the cause for my stalling out and the loss of RPMs on the road. I surely hope so, at least. That is my primary concern.

Thank you for the suggestions. I'll check out the car tomorrow morning and let you know what I find out.