First Time PCV now P0505

[linuxsuperuser]

Hey Guys! Ive been driving a 98 S70 NA with about 168,000 miles. It was a hand-me-down from my parents, so naturally after falling in love with the car (The 2 DC snow storms were no match!), I've been cleaning it and tuning it up as much as possible. I was inspired to replace the PCV/Flametrap after seeing pools of Oil under the plastic spark plug cover and noticed the car was burning a small amount of oil after hundred mile plus trips (no smoke).

During the Job, I followed the procedures from this site: http://www.lakesidedp.com/uploadpics/pcv/index.html
It took most of my day but was uneventful, after taking the manifold off..
1. Cleaned the Throttle Body / Replaced stock S70 Throttle Plate with one lacking the rubber piece. Installed with new gasket and greased throttle linkages/cable.
2. Cleaned Intake Hosing and used CRC MAF cleaner on the MAF when it was disconnected. Greased various O-Rings.
3. PCV - All new Hoses and new worm style hose clamps. The hose running to the passenger side of the manifold and to the intake was installed with a new O-Ring as well. My only doubt was a metal fitting that connected the bottom of the PCV box to the block(URO Brand from FCP PCV Kit), it had a rubber interior and was a tight fit because of this I assume it is okay to not use hose clamps?

After Install, the car ran fine. The idle was smooth and around 900-850 RPMs. After driving the car for 20 Min, Cel Light. Code P0505 (Idle Air Controller) on my OBD2 scanner and it would not stay off after resetting the DTC codes or a battery disconnect. After this the car began running roughly during idle when in drive but never was close to stalling out. The car was at the Volvo shop today, they couldn't pin the problem but said something like "The Car's computer is not able to predict/maintain the exact pressure of the manifold. Something about messing up Air/Fuel Ratios" No additional codes also.

To me this sounds like a small vacuum leak. The next time I can work on it, I am going to break it back down and see if I made any mistakes during the install. It sucks that it's not something obvious. Anything advise that only comes with experience?

Thanks!

[jblackburn]

Well, first of all, congrats on your first big repair! That's one of the most frustrating and time-consuming repairs on one of these cars.

Your issue sounds like a vacuum leak to me too. The question is where...

Is the PTC hose that attaches to the left side of the intake manifold on securely? Mine popped off about 12 times as I was trying to attach it at the back, and I got quite annoyed with it. Eventually I had to have my brother hold one end while I attached it to the PTC.

You could try cleaning the IAC valve, but I'm not sure that it would help.
http://www.volvoforumsrepairs.org.uk/800Repairs/iac.htm

I crimped the intake manifold gasket the first time I reinstalled it - the bottom corner of it got kinda kinked while I was trying to screw it back on. You really need to have a helper with this job. My car ran horribly the first time I started it up afterwards (not a great feeling after you've been slaving away at it for hours), but as soon as I took the manifold back off, I saw what I did wrong. I'm not sure that this is your problem either...you say that it ran fine when you first started it.

[linuxsuperuser]

Thanks for your response!
The small vacuum line on the passenger side of the manifold was very difficult to get on. I managed to get it about half way on before declaring it "good enough". I will see if putting a hose clamp over it and resting the code makes a difference.

I wish it was something simple like crimping the manifold seal, it has to be a very slow leak or I think the car would have run badly like you said.

It might be a few days before I can work on my car again, I will post the solution to the forum when (if) its found.

[Ozark Lee]

Sudo,

I have a couple of methods of detecting intake leaks and it largely depends on what I have in the garage that I can spot at the moment. I either use an unlit propane torch waving at all of the likely vacuum leak areas, including a run up and down the intake manifold. Do that outside, not in the garage or bad things can happen or spray carb cleaner around the various vacuum areas. If you hear a change in RPM then you found your leak point.

...Lee

[linuxsuperuser]

Thank You for all the useful information.
For my propane test, I used some old tubing hooked up to an old camping stove regulator so I could stick the hose everywhere and down by the pcv trap, nothing though. I am starting to wonder if this is even a vacuum leak. I did clean the IAC valve and its flapper is now moving freely when shaken. Also I ordered new intake hosing and a new IAC valve based on other's experiences with the most annoying p0505 code.

After cleaning the IAC valve, the time it took the CEL illuminated increased. Also the engine starts idling funny (Not close to stalling) only after the CEL light comes on. But what are the chances of a clogged PCV instigating the failure of the IAC valve? Could this be a MAP sensor problem that originated from handling the manifold?

Keith

[vjaneczko]

Keith, any updates?

I've done the PCV job and since then I've gotten the P0505 three times, each about a month apart. I cleaned the IAC, checked for vacuum leaks and at this point I'm just scratching my head.

[linuxsuperuser]

I am no longer experiencing the P0505 problem, *update - sorry for taking so long.

Some Observations.
1. Idle Droop was more profound in warm weather, worse with AC on.
2. Sunoco 93 Ultra Gas made P0505 go away but only when I was using it. Premium idle droop was apparent but P0505 never came on.
3. Disconnecting the battery was my only chance to get that light to stay off for any significant period of time.

Unfortunately their was not one specific "solution" to this problem. Here are a few procedures, which I believe contributed to fixing P0505 the most at least in my Volvo.

Possible Solutions
Replace these Parts: Engine Oil Cap Rubber Gasket; all the Rubber Joints connecting the EVAP solenoid to its filter and the filter itself; Front O2 if never done before.
Check these Parts: Air Box Thermostat - make sure its not stuck to the exhaust side; Ignition Coil - Look for Sparks in the Dark; B+ Cable - Procedures for Check; Also I noted that my PCV ports on the engine itself was clogged and switched to Mobile1 0w40 for its detergent properties, hasn't hurt.

For about 5,000 miles.
1. Use Chevron Techron in the next 2 tanks of gas, the big bottle for 21 gallon fuel tank.
2. Find an (although expensive) high grade of gas like Shell V-Power or Sunoco Ultra 93 and begin using it during the interval, avoid switching brands.
3. Finish Up Working on your car, to where you are comfortable leaving the engine alone for 5,000 miles.
4. Drive till the engine is at operating temperature - gas it for about 15mins. (And ensure that you have Premo Gas that has not been mixed with anything less)
5. Disconnect the battery, wait 5 mins, reconnect it.
6. Quickly restart and Idle the car for 25 mins minimum, without any loads on engine. AC, Headlights, Fan off. Before turning off car, shift into each gear, only if your car is an automatic, and hold each position (R-N-D-3-L) for about a minute to set the initial shift timing.
7. Drive alternating between styles both slow and fast; city and highway. Do not use the AC at Idle or in Stop and Go traffic for the 5,000 mile interval, the ECU does not adapt when the compressor is on. Do your best to drive the car in a way that prevents it from Drooping below 850 rpm, my car would get the P0505 when stopping or after restarting the car with an already warm engine. The problem was made worse on days with large temperature differences or if I loaded the electrical system immediately after starting the car.
8. Avoid Disconnecting the Battery; or expect a return of P0505
9. Towards the end of the period, test the ECU by using a lower grade of gas.

In Conclusion:
I personally believe the problem is caused by the adaptive fuel trim or map in the ECU or lack of a properly populated fuel table. Every time the battery is disconnected, the car forgets its unique adaptations. Because the car is not factory new anymore and broken-in, the Baseline fuel trim table could be off enough to prevent the car from idling correctly under varying environmental conditions such as temperature and fuel type. It can take several thousand miles and a change in season to rebuild the fuel table but since that point, I've been P0505 / CEL free. I stopped regularly disconnecting my battery before working on my car and It will also idle correctly with any grade of gasoline, with or without the AC in hot weather too.
More about Fuel Trims: https://www.matthewsvolvosite.com/forums ... =5&t=21123

[jblackburn]

Hmmmmmm interesting! Thanks for the update!