2000 Volvo S40 Hard Start Low Idle

[Porkers]

Hi, first time poster here. I just recently purchased a 2000 S40 with 108k on it. It had codes P1446 P0037 P0505 P0245 P0031 P0130 and P0445. It would start after 10-15 revolutions and run rough. It would stall if I didn't keep my foot on the gas. My reader said to change the PCV valve. I did that job and nothing changed. I checked for vacuum leaks and I absolutely cannot find any. I tried changing the IAC valve and MAF sensor. Now I have a MAF code. So I put the old one back and I still have that code. So I thought that it had to do with the purge valve because of the P0445 code. So I checked that I found that it wasn't sealing. I replaced that, but no change. So I checked the plug and I'm only getting 3.4V on the power side. So I did my own power setup to see if the low voltage was the problem. I hooked the power side to the battery and the ground side to the wire going to the ECM and the idle evened right out. No problems at all. So I go to clear the codes, shut off the car, clear them, and start it up again. It took a second to catch, but nothing like before. And the check engine light stayed off for maybe 5 seconds and then it started running rough again. I went out to check that my wires were still connected. They were fine. I go and check the codes again, and now it's all the same codes, just except for the P0445 code! But I can disconnect the wires, then reconnect them and it seems to completely smooth out. After some more looking, the IAC plug is also low, like 2.0V. Could that be why it's trying to stall? Is their wiring connected? Is there anything else in their circuit? Any help is appreciated. Thanks

[RickHaleParker]

? Is their wiring connected?

Yes .......
System relay Feeds current to:
engine control module (ECM).
fuel pump
crankcase ventilation's heater
Turbocharger (TC) control valve. ... P0245
injectors
evaporative emission system (EVAP) valve .... P0445
Ignition coils
idle valve (IAC) .... P0505
both heated oxygen sensors (warm-up) ... P0031 P0037 P0130
mass air flow sensor (MAF)

You might want to go digging in the Fuse/Relay box. The system relay is the one in the rear driver's side corner of the relay box. symptoms are pointing toward a problem on a main electrical buss.