Guys need help in diagnosing a problem on my 95 530iA.:help I completed a head gasket change on my engine but I can’t seem to get the car running right. I can start the car without a problem and it idles well. When I put my foot on the gas pedal the engine immediately loses power but then surges back to normal idle. As the engine warms I can add more power but will eventually lose power and then surge back to idle. Once the engine reaches operating temperature the problem goes away. :eyecrazy
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I’ve replaced the following components:
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- Mass Airflow Sensor
- O2 Sensor
- Air Filter

My 535i was doing the same and that was down to the Airflow meter which had jammed closed and wouldnt open. Sounds like its a leak somewhere in the vacuum system, start with the hoses for any leaks and make sure the air flow box is swinging freely, mine buckled after a backfire, the joys of an LPG system :rolleyes

Check engine light?

My 535i was doing the same and that was down to the Airflow meter which had jammed closed and wouldnt open. Sounds like its a leak somewhere in the vacuum system, start with the hoses for any leaks and make sure the air flow box is swinging freely, mine buckled after a backfire, the joys of an LPG system <?xml:namespace prefix = v ns = "urn:schemas-microsoft-com:vml" /><v:shapetype id=_x0000_t75 stroked="f" filled="f" path="m@4@5l@4@11@9@11@9@5xe" o:preferrelative="t" o:spt="75" coordsize="21600,21600"><v:stroke joinstyle="miter"></v:stroke><v:formulas><v:f eqn="if lineDrawn pixelLineWidth 0"></v:f><v:f eqn="sum @0 1 0"></v:f><v:f eqn="sum 0 0 @1"></v:f><v:f eqn="prod @2 1 2"></v:f><v:f eqn="prod @3 21600 pixelWidth"></v:f><v:f eqn="prod @3 21600 pixelHeight"></v:f><v:f eqn="sum @0 0 1"></v:f><v:f eqn="prod @6 1 2"></v:f><v:f eqn="prod @7 21600 pixelWidth"></v:f><v:f eqn="sum @8 21600 0"></v:f><v:f eqn="prod @7 21600 pixelHeight"></v:f><v:f eqn="sum @10 21600 0"></v:f></v:formulas><v:path o:connecttype="rect" gradientshapeok="t" o:extrusionok="f"></v:path><?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:lock aspectratio="t" v:ext="edit"></o:lock></v:shapetype><v:shape id=_x0000_i1025 style="WIDTH: 11.25pt; HEIGHT: 11.25pt" alt="" type="#_x0000_t75"><v:imagedata o:href="http://images.bimmerforums.com/smilies/rolleyes.gif" src="file:///C:\DOCUME~1\ANGELE~1.GON\LOCALS~1\Temp\msohtml1\01 \clip_image001.gif"></v:imagedata></v:shape><o:p></o:p>


Whats an air flow box???


Check engine light?<o:p></o:p>
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Flashes on when I have the loss of power but then goes away when the engine surges back. No fault code is saved on the computer.

aye sorry about that, been a long day at work sniffing preptone, I meant the air flow meter, not sure on the 530 but on the 535 it sits on top of the engine connected to the air filter.

On our cars, it is a MAF. Black box between the airfilter and engine intake. Might get some MAF safe cleaner and check that.
Also, might try unplugging it and see what happens.

He's already changed the MAF.

Sounds like a terrible vacuum leak. Did you inspect the intake bellows(large accordion shaped hose going into the throttle body) for cracks? Also make sure that all hoses are connected to the brake master cylinder and check all vacuum lines for leakage.

If it was a vac leak, then the idle would likely be terrible, but that is certainly a very possible culprit. Since it is temperature dependent, perhaps the ECU isn't getting a signal it needs, like knock or throttle position.

Do all of your gauges seem to present correct info? (coolant temp, mpg, etc?)

You say you just changed a head gasket. Is there a chance that you pinched the intake gasket a bit so it leaks when cold but seals once it warms up?

Guys,

Been doing some research, tell me what you think. I think the possible culprit it the Air Temp Sensor in the intake manifold. I've found several websites that stated the following about cars manufactured by other companies:


"An air temperature sensor is used on fuel injected engines. The purpose of an air temperature sensor is to help the computer calculate air density. A change in temperature changes the resistance in the sensor. Simply stated, the higher the air temperature gets the less dense the air becomes. As the air becomes less dense the computer knows that it needs to lessen the fuel flow. If the fuel flow was not changed the engine would become rich, possibly losing power and consuming more fuel."

One of the things I was not sure about but confirmed today was that the car is sucking fuel like crazy. According to the vehicle computer Im only getting about 12 miles to the gallon and the fuel gauge is dropping way too fast. My guess is that the loss of power is coming from me flooding the combustion chambers because the injectors are getting a screwed up signal from the computer. Once the engine reaches operating temp the signal to the ECU changes and the car runs smoothly. God I hope this solves my problem.

BMW doesn't use an IAT sensor specifically, I think they use the MAF's readings for that.

Like you said, though, it acts fine when it gets warm, which makes me think the coolant sensor is a culprit, as it also tells the DME how to act, much like the O2 sensor.

I agree, sounds like coolant sensor.

So I think it is either 9 here
http://realoem.com/bmw/diagrams/p/t/87.png

Or 8 here
http://realoem.com/bmw/diagrams/c/k/3.png


PS: How did it go pulling the heads? I wasn't able to get the driver side head off so I lifted it up 6 inches with a winch.

PS: How did it go pulling the heads? I wasn't able to get the driver side head off so I lifted it up 6 inches with a winch.

Once I got a head bold with a sheared head out it pulled right out. I plan on posting with all the details but work is kicking my ass and I still can't get the car to run right. Something is seriously wrong with fuel management system.

Please focus on the MAF sensor/connections, I had a similar experience with a Nissan which uses the same system in reading airflow(the MAF is the air temp. sensor), also replaced the MAF then but the problem remained, turned out I got a defective replacement part.
Its posible you have the same problem, also check and clean all the terminals/wires leading to the MAF. Goodluck!