Two Sensors Die at Once? 98 v70 T5

[erikv11]

That little plastic connector between 1a and 1b is just a hollow tube, I am actually certain of that.

Along those lines, disconnect at 1, plug the open end, see if the idle goes bad. Then the FPR runs without vacuum which would be an issue at high RPM but definitely not at idle.

Unfortunately there's still no good evidence that anything is dumping fuel into the IM as far as I can tell. If only the idle was bad now, and could be predictably so during these tests ...

[WagonLagan]

That little plastic connector between 1a and 1b is just a hollow tube, I am actually certain of that.

Along those lines, disconnect at 1, plug the open end, see if the idle goes bad. Then the FPR runs without vacuum which would be an issue at high RPM but definitely not at idle.

Unfortunately there's still no good evidence that anything is dumping fuel into the IM as far as I can tell. If only the idle was bad now, and could be predictably so during these tests ...

So plug the vacuum tube, leave the FPR open. Rev it to high RPM and see what happens?

And once the idle is bad again, I'll try messing with the IAC. Should I also try something with the FPR?

[erikv11]

No, I meant you can "plug the vacuum tube, leave the FPR open" at idle. If you rev with no vacuum on the FPR then I think it will stumble, based on my understanding of how the FPR works.

If the idle is predictably bad that's when you want to check for fuel in the vacuum lines, or do the "plug the vacuum tube, leave the FPR open" test.

[abscate]

Can you get to an Advance Auto, borrow a pressure gauge and monitor the fuel pressure?

[mrbrian200]

FPR is probably ok. Idle raised when you plugged in the IAC- if that was on a cold engine that would be normal.
If that was on a warm engine we might want to look at the coolant temperature sensor value. Leave the hood open for several hours so that the engine temperature will be the same or very close to ambient. Turn the key to the on position without starting the car and pull up the sensor value with the OBD phone app you pictured earlier. Note the value and compare it to ambient.

[WagonLagan]

Hey guys, I apologize.

I greatly appreciate all the help you've given me, but sadly I just don't have the time or energy to keep whittling away at this.

I scheduled an appointment with my indie who specializes in Volvos. Hopefully he'll be able to figure it out.
I'm going to hand them a list of suspect systems and things I've already done, thanks to you all.

I'll report back so you all will get to know what the heck it was.

If you guys have any thoughts on this list, I'd certainly welcome input:
1. First thing I'm going to have on there is a smoke test, because I can't do a thorough one with my junky smoker.
2. Electrical wiring/connections to TPS and Baro sensor (why else would TPS code keep popping when there's a brand new one)
3. IAC
4. MAF

Thank you all for all the guidance and ideas. I'm disappointed I have to indie it.

[erikv11]

... 2. Electrical wiring/connections to TPS and Baro sensor (why else would TPS code keep popping when there's a brand new one)
...

Bad or dirty connector?

Let us know how it turns out, I'm sure many are curious.

[mrbrian200]

Chances are he'll start from scratch so as not to potentially miss anything.

[erikv11]

Chances are he'll start from scratch so as not to potentially miss anything.

ya think? Sheesh I hope so.

[WagonLagan]

Urrrgggg. $300 and nothing was resolved.

Naturally he chased the codes, and he replaced the baro sensor, which of course did nothing.

The issue has gotten worse if anything.

However, since it has gotten worse, I was able to test a bit and I think I found the issue.
When I start the car, it revs up to 3k and very slowly tapers down. It also changes if I shift gears.
If I unplug the IAC while it's revving, it drops right back down to something semi-normal.

I ordered a used IAC and we'll see if that fixes it. Driving with it unplugged for now.


I suspect the IAC is holding wide-open most of the time, and flooding the engine with air. So when it's injecting in extra gas at start up, it's not stalling because it has both of what it needs.

Then after it tones down the idle gas feed when the car warms up, the IAC is still flooding the engine with air, killing combustion and stalling it out.

Still not sure why the TPS is the code that keeps throwing. I'm confident that if it isn't the IAC itself, it's a wiring/electrical issue. Are the IAC and TPS on the same wiring?