xB hesitates at Start up..
 

Hi all, I'm new to the forum. I have a 2006 xB with 63,000 miles that kind of hesitates at startup. It's only does it first thing in the morning or after it's been sitting for a few hours in the cold.
It hesitates a little at about 1,000 rpm, then goes up to 1,200 or so (that's an estimate) then goes back down to 1,000 before it warms up down to 600 or so. It's hard to explain but it's kind of a slight lugging sound.
Sounds like it's having kind of a hard time for about a second or a little less. When it's warm it just zooms right up to 1,100-1,200 real smooth.
I have new spark plugs, new battery, new throttle body, new idle control valve ( I think, my mechanic wrote I v idle air, I'll ask him & make sure )

Any ideas? Maybe dirty fuel injectors? If so, what would you recommend for cleaner, or should I have them cleaned?

Thanks!

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It is most likely a fuel supply problem.

First off, I would inspect all the fuel delivery hose connections. Look for signs of leakage. If you suspect any connection of leaking, I would replace the O rings within any suspect connector.

If black smoke comes out of the tail pipe when you first start the engine it could most likely mean that you have one or more leaking fuel injectors.

If no black smoke......you may have a bad fuel pressure regulator (which almost NEVER happens). Pull the little vacuum hose off the fuel pressure regulator and look in the hose. If you see gas in there, it means you have a bad regulator and it needs to be replaced.

If no gas is in that vacuum hose, I would next suspect the problem is a faulty fuel pump check valve. The fuel pump check valve is designed to keep the pressurized fuel from leaking back into the fuel tank. It is difficult to test/inspect the check valve because it is an integrated part with the fuel pump module. The fuel lines that come off the fuel pump are a type of hard neoprene plastic. They can't be pinched or kinked because the line might crack, but normally, what I would do is pinch closed the line with vice grip pliers and leave the line pinched over nite (thus keeping the fuel from draining back into the fuel pump........next morning, remove the pliers and immediately start the engine. It should fire right up with no hesitation. If it starts up like normal, I would replace the fuel pump. Normally, the way most people correct a faulty check valve is to replace the entire fuel pump module.

Fuel System leakdown failures can be caused by a leaking fuel injector(s), a bad fuel pressure regulator (FPR), or a leaking fuel pump check valve. When this happens, the fuel rail loses pressure and the car is difficult to start when it's been sitting for a while. When the engine is turned over, if the fuel rail is low on pressure, it takes the fuel pump a while to pressurize the fuel rail so that the car will get enough fuel to start.

Wow, thanks! I'll run this info by my mechanic right away. Much appreciated.

I would like to add that it does start up right away, but kind of hesitates or drops rpm's a little once it gets to 900-1,000 or so. Yesterday morning it did hesitate for the first time in the lower rpm's, probably 500 or so. Still started right away though. Figured I'd put that out there in case there was a misunderstanding. Just want to make sure to get my mechanic the right info. Just can't afford any trouble shooting, been putting way too much into cars lately! Thanks