Reads like the solenoids are not working...

I have been throwing codes P1150 & P1120 fairly consistently, both are for Manufacturer Controlled Fuel And Air Metering. Recently though I also through code P1531, Camshaft adj bank 1- I was able to actuate bank 1 and car started running rough and when I deactivated it smoothed back out. Same for bank 2. Have also seen some Oxygen sensor codes (all are new)

I checked a bunch of reading and found all the ones listed below out of spec: I've included High/Low specification and actual reading
Other symptoms and idle bounces around & sometimes when hot wants to stall out. Other than that car runs good

Based on what I am seeing below should I suspect the MAF????

1998 5 speed 176K miles

• RPM SB: 660-700 IS: 790
• Load SIgnal (ms) SB: 1 To 1.6 IS: .8
• Mass Air Flow (kg/h) SB: 14.5 to 19.5 IS:11
• Spec Air Mass (Kg/h) SB: 16 to 18 IS:12
• Spec Air Adaption (Kg/h) SB: 2 to 4 IS: -4
• Injection Time (ms) SB: 2.6 to 3.4 IS: 2.4
• Range 2, Cyl 1-3 (FRA) SB: .98 to 1.06 IS: .95
• Range 2, Cyl 4-6 SB: .98 to 1.08 IS: .96
• Range 1, Cyl 1-3 (TRA) SB: -.1 to .1 IS: .37
• Range 1, cyl 4-6 SB: -.1 to .1 IS: .37
• Rough Running threshold SB: 7.9 to 10.5 IS: 6.9

at the wiring harness and clear the codes -- to reset the adaptation values to their defaults -- and then drive the car to see if the previous behavior and error codes return.

Then after a 30 mile drive or so -- enough of a drive to give the DME time to go through all readiness monitor tests -- reconnect the MAF, clear the codes again, and test drive the car again. The results of this then can help you condemn the MAF or prompt you to look elsewhere.

There are enough readings out of whack but some might be wrong collaterally.

Tell me about the car? Are you running an aftermarket air filter? What is the history of the car? How old is the AOS? I've gone through more AOS's than MAF's with my 02 Boxster. In fact I've gone through as many oil filler tube caps as MAF's. I replaced what proved to be a perfectly good MAF when the real problem was a leaking oil filler tube cap. When the replacement MAF failed after maybe nearly 100K miles I installed the original MAF -- which thankfully I saved -- and it worked fine and has continued to work just fine since.

Another shade tree mechanic trick is to try to unscrew/remove the oil filler tube cap with the engine idling. While the cap should unscrew just fine you may find you can remove the cap against the pressure difference inside and outside the engine due to a bad AOS that has subjected the crankcase to extremely low pressure. However, even if you are able to remove the cap without undue difficulty this doesn't let the AOS off the hook.Enough have failed and not manifested this behavior that the AOS would not be entirely eliminated if the cap came away without a struggle.

While either the MAF or the AOS could be at the root cause of the engine's behavior I can't advise you to replace either item based on what you have posted.

BTW, I did a search for P1150 and P1120 and these error codes do not pop up at all for Boxsters. I visited renntech.org and these codes are not in the data base of error codes for the early Boxsters.

Are you sure about the numbers?

P1531 -- camshaft adjustment for bank 1. I can tell you when the VarioCam sensor/actuator on my '02 went bad this was a pending code. The engine wasn't running very well. I did check fuel trims and noted one bank's were quite erratic. The tech later told me that it was due to the DME attempting to get the O2 sensor readings from the bank it wanted to get and had this continued the bank could have misfired as the mixture got too far off. It could be possible in your car's case the underlying problem is bad VarioCam solenoid or actuator and the other readings/error codes arise from that.

But like the MAF and the AOS I can't advise you to replace the solenoid/actuator. These are quite expensive and costly to replace. It cost me around $3K to replace both in my Boxster.



Edited 1 time(s). Last edit at 07/13/2014 11:32AM by MarcW. (view changes)

Car is 100% stock- no aftermarket anything in it

NEW AOS this spring... As I autoX and track the car a lot so I change the AOS every 2 years if it needs it or not

I was having the exact same issues prior to new AOS so I have pretty much ruled that out.

Checked at oil cap- no issue. I originally suspected (some what still do) a vacuum leak. But I have tried all the old school tricks with spraying starter fluid around etc with no success of finding any indication of an air leak anywhere

I agree that some of the out of spec reading could be collateral to what ever is wrong. The air flow reading being out make me suspect the MAF, but I am just not 100% sure

then unplug the MAF and see if the problem goes away.

If I unplug the MAF will I see a significant change in values for air metering etc?

I will unplug and drive

The time or two I did this I was simply attempting to determine if the behavior/symptoms were possibly MAF related. In one case I recall they were not. They were related to a bad AOS. The first bad one. I do not recall the specifics of when I disconnected the MAF the second time but I'm pretty sure the MAF wasn't the problem this time either.

It reads like the AOS is unlikely to be the problem, which promotes the MAF up the list of suspects, but I can't advise you to replace the MAF with no more to go on that a moderate suspicion.

I mean you can throw parts at the behavior if you want, but you'll get no real encouragement from me. 'course, if you disconnect the MAF and the behavior goes away and them comes back when you reconnect the MAF, how much plainer do you need the writing on the wall?

Absent anything better to do/try do the MAF disconnect.

Might as well toss in that if at any time the engine starts running worse, making scary noises, shut off the engine. It ain't the MAF… But it is time to get the car to a professional for diagnosis and repair.

Disconnected MAF and went for ride. When IO returned no difference in anything. All reading still the same.

BUT- I found an old bad MAF and installed that- Immediately got a MAF code. However, idle still high and all reading basically the same. I think this starts ruling out the MAF as the issue.

What I find interesting is my cam shaft deviations are both ZERO. when I activate bank 1 it goes to 1 then when I stop it goes back to zero. Same for bank 2.

I see so many folks with deviations in the 5, 6 or higher range... not sure why mine are zero with 176K miles?????

means there is too much air getting into the engine. If it's not the ICV or the throttle body then you have a leak.

Since the AOS was recently replaced, that's a prime suspect. Did you reuse the rubber bellows? It also could be one of the vacuum lines has become disconnected or that one of the sections of the oil filler tube (particularly the bellows at the top) has cracked. That is common on the early cars. If you spray a flammable material in each suspect area the idle will go up momentarily if the engine sucks it in.

Air leak has been my number 1 hunt up till now. This issue existed prior to replacement of the AOS, no change at all once AOS replaced. I have and tried the starter spray all around with no success. Idle ranges 760-840 ish. When stable and not bouncing generally right at 800 RPm

Quote
Ollie
Disconnected MAF and went for ride. When IO returned no difference in anything. All reading still the same.

BUT- I found an old bad MAF and installed that- Immediately got a MAF code. However, idle still high and all reading basically the same. I think this starts ruling out the MAF as the issue.

What I find interesting is my cam shaft deviations are both ZERO. when I activate bank 1 it goes to 1 then when I stop it goes back to zero. Same for bank 2.

I see so many folks with deviations in the 5, 6 or higher range... not sure why mine are zero with 176K miles?????

At least the one on bank #1.

This can be a solenoid problem or an actuator problem or possibly even a wiring/electrical/DME problem.

The trouble is the solenoid is buried under the camshaft cover. All you can do is ensure that when the solenoid is triggered you see the proper voltage level at the solenoid connector.

If the voltage is right then the solenoid or actuator is suspect. You are looking at solenoid replacement. However, my info is that if the solenoid is replaced the actuator should be replaced too. There is no way to test the actuator and if it is bad you will not know this until after the engine is buttoned up. While the engine doesn't have to come out the exhaust system, and some other things have to come off/out and the camshaft cover has to be removed and the labor to do this, that is get to the solenoid and then button the engine up again is quite a few hours of labor, IIRC 6 or maybe more. The camshaft cover has to be properly sealed and the camshaft cover bolts should not be reused.

If just the solenoid is replaced and the actuator proves to be bad, the job has to be done twice and the actuator is even more expensive part and requires a bit more labor to get to and remove/replace. You could be facing a $5K to $6K repair bill after it all said and done vs. a $2.5K to $3K repair bill.

If the right voltage doesn't appear at the solenoid connector when the solenoid is activated this strongly suggests a wiring/DME problem. There are several possible explanations for bad wiring/connector. The DME can be bad -- the output of the pin or pins used to trigger the solenoid have failed -- or possibly something on the DME board has failed. The DME output doesn't go directly to the solenoid but goes to something else nearby the DME and then this something else is responsible for sending the voltage signal to the solenoid. It is this something else that can have failed, perhaps a transistor or whatever makes up the something else.

I do not have a wiring diagram handy but if there is just one output that controls both solenoids and if both are not triggering, and if both do not have the right voltage signal when triggered this suggests a common failure and this points to something at the DME or that something else I mentioned above.

While diagnosing this and possibly even fixing this is within the capabilities of some DIYer's you are dealing expensive parts and lots of labor to replace them. You want to be sure what is wrong so after you do the work, spend the money, the car is fixed and fixed right. I would therefore suggest you enlist the aid of a pro Porsche tech who knows these cars very very well.

I will check voltages etc as suggested. I activated the variocams on both banks at least 20 times hoping if stuck it unsticks (I know, wishful thinking).

I will let you know how the voltages look in a few days when I can get to them.

I would clean both and check for smooth operation.

While you're at it, check the plugs and wires for both the idle control valve and throttle position sensor.

but an ICV and this can get dirty and cause some problems.

Pulled TB/ICV... both seemed fairly clean and operating smooth but cleaned them anyway- this had no effect on the issue

The MAF readings are way too low. Check the MAF parameters for a bad MAF. If its ok, then low MAF readings indicate a vacuum leak.

I put a known good MAF in tonight with no change... agree with Vac leak, this has been my main thought BUT I can not find one AHHHHHHH

technique taught me was to use an aerosol can of carb cleaner and spray it along where the carb (this was a while back…) connects to the manifold and where the manifold connects to the head or heads. If there is a leak the engine will react as it gets the carb cleaner through the leak instead of air.

Now the Boxster engine is a bit of a problem in that some notorious air leaks are not found at or with the intake system proper.

For instance, there's the good old AOS which as it transitions from good to outright no good can have a stage of failure that is essentially an intake air leak. The AOS passes too much low pressure to the crankcase and this results in an excess of air getting fed to the intake *after the MAF* as the connection from the AOS to the intake is at a hose connection located directly downstream from the throttle body.

If the AOS is intact and functioning properly other air leak sources have been the oil filler tube. This can crack or split and when the crankcase is under low pressure -- it is under low pressure most of the time -- and can allow air into the crankcase and thus on into the intake via the hose that runs between the AOS and the intake.

A more subtle leak can be the oil filler tube cap. This is a particularly insidious leak -- I speak from direct experience -- as it exists only at low engine speeds. The amount of air that manages to get past the cap is large relatively to the air needs of the engine at idle but small relative to the air needs of the engine at higher RPMs. As I've mentioned before it was an oil filler tube cap leak that I misdiagnosed as a MAF problem and replaced a perfectly good MAF when all that was needed was a $15 cap.

The cap is an easy thing to eliminate. When the engine is running and is at the same temperature as when the symptoms of an intake leak are present or would be present one can try to move the cap about -- while still screwed down tight -- and see if he can get a reaction from the engine, possibly even hear the air rushing past the cap's seal.

The oil filler tube is harder to eliminate as a source of an intake leak. Usually a leak is spotted visually. The car has be lifted in the air so a through inspection -- using a mirror on a stick if necessary -- can be made of the tube. Sometimes a leak of this item is highlight with an oil stain.

There are various vacuum hoses that can and will over time age and possibly at some point crack or split. Generally these fail where the hose slips over its connector spigot at the bottom of the hose. When engine work is done if these hoses are disturbed they can crack/split at this point. Afterwards, the hose tends to want to return to its position so this can work to close the split or crack and make it hard to see, but of course it will make itself known when the engine is running.

These hoses are checked visually with a bright light and possibly even a mirror on a stick with the engine off. Run each one from one connection to another feeling the hose giving the hose a gentle flex looking for, feeling for a crack or split.

With other engines I've run the hoses with the engine idling but these were engines with good access from the top. For a Boxster engine this is probably a job best left to a professional tech, though I believe he'd probably attempt to ID a possible bad hose with the engine off.

(I can also add that if a hose was suspected I'd just replace the hose. I kept a good stock of vacuum hoses at home and would just cut a new hose of the proper size to length and remove the old hose and install the new hose. Course this may not be practical if the hose is formed/shaped rather than just a plain old piece of hose held in place with hold downs.)

A very subtle intake air leak can happen upstream of the MAF say at the air box. While the air is introduced ahead of the MAF and nominally metered by the MAF air flow from the leak is not as laminar as it would be otherwise and the MAF requires a degree of laminar air flow to properly function and the MAF doesn't properly measure the amount of air flowing into the engine. Most often symptoms from non-laminar air flow arise from the use of aftermarket air boxes/filter systems but a stock system that has failed or been disturbed, in some way compromised due to work in this area can also create non-laminar air flow past/through the MAF. The MAF output can be chaotic and strongly point to a bad MAF, a natural assumption, but of course a new MAF doesn't help.

which I list above.

Quote
Ollie
I put a known good MAF in tonight with no change... agree with Vac leak, this has been my main thought BUT I can not find one AHHHHHHH

Pinch off the hose small hose thats connected to the throttle body at the same connection for the AOS. Thats a line that connects to the EVAP system. If the MAF values go back to normal, then the vacuum leak is somewhere in the EVAP system.