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Matt, Engineer
Category: Oldsmobile
Satisfied Customers: 20395
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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Oldsmobile Alero: Been having a problem where at stops the

Customer Question

Been having a problem where at stops the car's idle drops slightly then returns. It does it sometimes through out the drive and some times its barely noticeable. It also shakes at stops. I have a scanner and when i used it i got PO107. I already addressed this code by changing MAP Sensor. Icleaned the throttle body and Throttle Position Sensor and the Idle control valve. I still got the same symptoms after that, so i took to a mechanic. He installed manifold gasket. It seems that the idle improved while the shaking did not. That was for about 1 day. Everything came back.
I then changed the engine mount. That has solved the shaking, however, the idle dip occurs sporadically. So I still have the idle dip which why i am on this service. The car is a 1999 Oldsmobile Alero 4cylinder. Electric windows, cruise control, and drive seat.
Today, I used a different scanner that picks up more codes. This scanner picke up 13 codes all starting with the letter B. Which i have learned is the Bode Control Module. Here they are:B2575, B2585, B2577, B2578, B2587, B2588, B2648, B2600, B2601, B2602, B2603, B1001, B000
So this morning, I found and disconnected the BCM. I also then disconnected the ECU. After connecting back the BCM and then the ECU, they were both off for about 1 hour, the car started right up. And, to my surprise it ran better then over. I took a*****and parked it for about 2 hours. I started the car and driving back as I waited at a fastfood restaruant with the car on drive in the drive through for about 15 minutes...the idle dropped and felt those same symptoms. I then did the scan and got all those codes again.
What is your recommendation?
Submitted: 5 months ago.
Category: Oldsmobile
Expert:  Matt replied 5 months ago.
HelloThis could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running. Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts. The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.Work your way through each possible joint one at a time and you should find it. I use a slightly flattenedpiece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements. It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine Might also be worth cleaning out the idle speed control motor / valve as these get clogged up with carbon and some brake cleaner washed through helps free things off. Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.if the engine condition is the same then chances are the meter or the connection to it is faultyAir leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them. This leads them to be quite intermittent in the case of mild leaksits also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residue On no account touch the sensor wires with anything physical as they are extremely fragile

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