asking for help troubleshooting P0174 current fault, P0171 pending fault

[backyard65bill]

2006 Volvo XC90, 4.4L, AWD, 181k miles. Starts, runs, drives very good, even with the codes.

I am asking for help/advice in solving this nagging problem: P0174 current fault, P0171 pending fault.

TEST DRIVE.
1. KOEO, connect scanner, clear codes with scanner. Rescan for faults, no faults.
2. KOER, drive approx 15 mins, 40 MPH max, some stop and go, pull over, park leave engine on
3. Idle for a few mins, exact 2 codes return

What I have done so far:

1. New vacuum tank (broken hose port) top rear of engine, passenger side. TEST DRIVE. Same codes.
2. New PCV valve and related hoses. TEST DRIVE. Same codes.
3. New air crossover manifold gaskets to intake manifold. New gasket, inlet manifold (30720333). New PCV hose located under the crossover air manifold. TEST DRIVE. Same codes.
4. Clean, bench test MAF. TEST DRIVE. Same codes.
5. Replace MAF with known good one, same MAP on gen2 Prius. TEST DRIVE. Same codes.
6. SMOKE TEST. Remove air filter box with MAF. Seal off inlet side of throttle body. “Tee” into throttle body to brake booster vacuum hose to smoke machine outlet. Turn on smoke. Could not find any leaks. Repeat SMOKE TEST. No leaks.
7. Reinstall air filter box and air snorkel to throttle body. Seal off air filter to keep smoke from coming back out to outside. SMOKE TEST. Minor smoke from snorkel to throttle body. Remove snorkel. Add small amount of silicon to throttle body where snorkel seals. Reinstall snorkel using new hose clamp. SMOKE TEST. No leaks. TEST DRIVE. Same codes.
8. Disconnect MAP sensor pigtail. KOEO. Test Vdc supply from ECU to chassis ground: 5.05vdc. Test ECU ground in MAP pigtail: good.
9. BENCH TEST. Remove MAP sensor from car. Bench test MAP sensor. Attach +5vdc (120vac to 5vdc, 400ma adapter) to MAP pin (ECU supply pin). Attach adapter ground to MAP sensor ground pin. Attach VOM multimeter to read MAP voltage output. Attach hand held vacuum pump to MAP vacuum port. Pump vacuum from 0psi to 26.57psi, and log the inHG readings on vacuum gauge.
10. Find other standard 1 BAR MAP sensor voltage/psi tables. Graph 2 standard MAP tables and my MAP table from 9. (See attached graph). My MAP differs quite a bit from standard. Search for MAP table from Volvo or anywhere else. Could not find any. Denso K0F-A9521-00 079800-7350.
11. So, took a leap of faith, and bought a used MAP sensor (MAP2) from eBay. BENCH TEST MAP).
12. Add MAP2 to graph. MAP and MAP2 look the same.

Getting ready to install MAP2 on vehicle, but, I don’t expect the faults are going to go away
Any help or advice from anyone here that understands my write up will be greatly appreciated.

thanks
Backyardbill

[Forkster]

@backyard65bill - sorry I missed this post.

My guess byb is that if you already replaced the MAF, it might be a worn-out oxygen sensor. Are the voltages to the O2 sensors reading at all? Also - do you have VIDA/DICE? That will provide more detailed diagnostic information.

[Forkster]

Also, in reading your MAF graph - that looks perfect. As you increase speed so will MAF readings. If it starts jumping around a bunch, that would be indicative of a faulty MAF sensor - but yours's is new correct?

[backyard65bill]

Fixed. After the last drive test failed with the same codes, I was at a loss to understand this problem. All vacuum leaks were repaired. Vehicle runs perfect. Same coded. Then I stumbled on a personal website of retired (I think) expert mechanic. He says "remember to clear out all computers anytime you fix anything". Do this by removing neg bat cable to 30 mins, to be sure. Else the accumulators won't be cleared. Scan tool won't clear these. And the codes will come back. Hmmmmm. I reset the computers as recommended. Drove XC90. The coded are GONE. it's been a month now and NO codes. Runs great.

Thanks to you and the other that helped me!