My 02 BMW 525i engine starts to stop runing when the gas pedal is pressed. The engine starts and drives fine when the engine is cold. However, after driving for a while like more than 20 miles, I mean when the engine warms up already, the engine suddenly stops when the gas pedal is pressed, like stopping in the traffic light or STOP sign and starts to drive. I replaced the idle air control valve, but it does not help. What should I check next? Any comments or suggestions are greatly appriciated, thanks.
You should check your thermostat and coolant temperature sensor. First check on the thermostat is just your temp gauge on the dash. Is the car running at normal temp by the gauge? The CTS is a bit more complicated - you need an ohmmeter, resistance specs on the sensor, and some way to measure the actual coolant temp.
The temp gauge looks fine when the engine is hot, it shows correct temp, meaning the needle pointing at the middle of the gauge when the engine is warm. When I press the gas pedal slightly (about 5 mm deep) , the engine speed does not increase (the engine feels a bit of retarded or does not correspond the pedal position), and press more the speed goes up as normal. The Engine Service light still lights up, I unplugged the power cords (+, -) from the battery to reset it. I cannot tell if the new idle air control valve is malfuntioned or not.
Get the engine’s code read next time it happens instead of disconnecting the battery. It will give us a clue as to what may be the problem.
If the engine idles fine there’s no problem with the IAC valve. But if the engine stalls as soon as you tip into the throttle from a stop, there might be a problem with the Throttle Position Sensor. Retreiving the code(s) from the computer might point to a problem with the TPS.
By the way. You run the risk of causing problems with modules/computers on your vehicle by disconnecting the battery. Read this article and it describes what can happen to some BMW models when doing so.
“The Engine Service light still lights up”
You say that as if you had mentioned it already. Oy is all I can say. Many auto parts stores will read your error codes for free. When they are done, they can clear the code(s) for you without messing with your battery. The code formats are: “P1234.” Get them read, write down the exact code numbers as shown on the code reader and post them.
Thanks for all the responses. The battery article from AA1Car is very knowledgeable and educational, I did enjoy in reading it. However, I think it is okay to unplug the battery cables (at least to the model/year of my BMW) if the manufacture manual does not warn the users to do so. I did read the BMW manual and it does not mention the risk of losing any preset data if unpluged the battery. I have not brought the BMW to LPS (local part store) to read the error code. Instead, I searched You Tube and found a video of cold start issue. The guy cleaned the MAF (mass air flow sensor) and solved the problem. Even my car does not have cold start issue, but I gave a shot. I believe either cold or hot engine will change the air density flew through the MAF and that is something I can try before take the car to LPS. I went bought a CRC MAF cleaning spray can and cleaned the MAF.
After I cleaned the MAF, the Engine Service warning light turns off after I started the car. I test drove the car yesterday and today, it ran fine and started up at traffic lights no problems. I will keep driving it for few days and come back to post any issues if happened.
I did not know when the manufacturers start to put MAF in the car, it is something new I learned from this incident. I will go check if my Accura 3.5 RL has one, if it does, I need to clean that one too, just for PM (preventive maintenance). Have a great day!
I hit the same problem again few days ago when I took a longer drive, the engine stalled and Engine Serice Soon lights up. I took the car to a local O’reilly store to see if they can read the error code, unfortunately they don’t. I did a search and ended up bought a OBDLINK reader. I plugged into a laptop to read the error code, it is P0209, Mass or air flow circuitry input is low. I ordered a MAF replacement part yesterday and waiting to arrive. I will post what happened after replaced the MAF sensor. I used the OBDLINK to reset the error code, look like this device can read lots of info, I am amazed.