Mass airflow sensor frustration

[sprocket]

Hello gang,

My 2000 996 C4 was throwing codes and idling at 1200 or even higher in spurts. I was told I should replace the MAS. So I did. When I fired it up it wouldn't even hold an idle before dying and it was very rough shaking the car. I put the old one back in, cleared the codes and lived with the high idle for the summer. I was then told that I should have disconnected the battery and drain any juice before reconnecting the battery after a new MAS instal. Supposedly the ECU needs to reprogram.

So, I did that. Put in new MAS, disconnect battery and reconnected. Started it and it won't hold an idle. When I give it gas it's really rough and sputters gasping and coughing. Is that because it's not reprogramed and needs to be run for a few cycles?

I'm at my witts end on this. Any help is appreciated.

Roch.

[Loren]

The MAF does little nothing at idle - it comes into play at 4000 RPM and above. You can disconnect it and it will not make a difference in how the engine runs at idle.

Have you cleaned the throttle body and butterfly? Most idle issues I have seen are gummed up throttle bodies where the butterfly is partially held open.

Try cleaning it and also clean the electrical connections on the throttle position sensor (located on the throttle body)

[ltusler]

Also if your TB is cable operated, there is an idle control valve behind the TPS. That may need cleaning also. Its pretty easy to remove the TB get a good look at things.

[wvicary]

What fault codes were you getting?

[Loren]

Also if your TB is cable operated, there is an idle control valve behind the TPS. That may need cleaning also. Its pretty easy to remove the TB get a good look at things.

It is a C4 and all C4's are eGas - so no throttle cable on this car.

[sprocket]

typical codes were p1128, p1130, p0507 etc....

So here is where i'm confused. if the MAF doesn't affect anything at idle, then why is that when I change it to the new one it won't even hold and idle and sputters, then I put the old one back in and all is fine (but it just idles high after a while)?

I did clean the TB during the summer and butterfly. All looked pretty clean. I haven't looked at the TB control valve though. Is that hard to get at? is it buried or can I see it when I open the lid?

Thanks.

[sprocket]

Also p0430 I believe

[Loren]

P1128 Oxygen Sensing Adaptation, Idle Range, Bank 1 – Above or Below Limit

P1130 Oxygen Sensing Adaptation, Idle Range, Bank 2 – Above or Below Limit

Possible causes:

– Incorrect signal from MAF sensor

– Intake air system leaking

– Fuel pressure too low

– Volume supply of fuel pump too low

– Fuel injectors fouled

– Exhaust system leaking

P0507 Idle Air Control at Stop – Above Limit

Possible causes:

– Throttle valve is sticking

– Leaks in intake air system

P0430 TWC Conversion, Bank 2 – Above Limit

Possible causes:

– Catalytic converter

I would start with common causes -- Leaks in intake air system

[sprocket]

Thanks. Do you have an idiot's guide, step by step process for that?

[logray]

Checking for intake leaks is usually best done with a smoke machine. The smoke will reveal any leaks in the intake system.

[xmac]

Some suggestions if you are adventurous and have some basic mechanical skills below. The problem is likely air leaks downstream of the MAF sensor. Throttle body "tee" pictured below (Porsche calls it the intake distributor Intermediate piece)

1. After removing the air filter assembly and disconnecting the big hose going to the throttle body, remove the throttle body (4 small bolts and an electrical connector) and make sure the o-ring seal behind it didn't get pinched or damaged (~$9 o-ring)

2. Check the plastic line on the left that clips into the tee holding the throttle body and make sure it is seated properly (visible in the picture near the upper left threaded insert - you pinch the ribs then wiggle)

3. Check that all of the hose clamps on the intake runner couplers are tight - 8 of them and hard to reach

4. Also check for a very small ~1/8" plastic tube that gets inserted into the bottom of the couplers. They are is the size of a coffee stirrer and held in place by friction. This is going to be tough to see so you may just have to check by feel.

After these checks, report back.