mcmaxian

This is my mother's car. It apparently was running fine when parked. Went to move it after it had been sitting for several weeks. It will start and run for about 3 seconds and then die. Will do it every time. When it is running it runs smooth and seems normal. Several times I did get it to keep running by putting the pedal all the way to the floor but it ran very very rough and probably around 300 rpm. It was pretty low on gas so I added 5 gallons along with something for moisture in the tank and some octane booster and then flushed out about a gallon of gas. No change. I came back a few days later with some tools and flushed a little more fuel out then tried to start it and found no fuel pressure. Eventually figured out the tank was completely dry. The gauge still reads 1/2 tank though. Put another 5 gallons in now fuel gauge reads 3/4 full. Maybe a separate issue? It has 55 psi at the rail with fresh gas. I found it will keep running indefinitely if I squirt throttlebody cleaner in the intake. Checked with a light and all 4 injectors have signal when running on tb cleaner. I pulled the rail and there is fuel coming out of the injectors. Tried disconnecting the MAF with no change. This is my first time working on anything MB. I noticed the idle control motor on the throttle body makes a continuous loud electronic whine is this normal? So basically it is getting fuel and spark but still won't stay running. Any ideas anyone?

Would a vacuum leak keep it from running completely? I blocked off the brake booster and another large vacuum line coming off the throttlebody.

What about the cam position sensor? What does it control? I will try disconnecting it the next time I am over there.

I have not checked for codes but will try to do that.

Anyone think I could have 55psi but still have a bad pump?