map40 wrote:
My 2006 C class with 154K miles runs great. A few months ago started to idle lower than usual, like 600 RPM. No, when hot, while idling, sometimes just stalls. It starts right back up. Any ideas?
Those are the signs of the throttle body throttle plate being gummed up.
Been there, done that with a 2006 F250 with 5.4.
The 5.4 AND v10 went to "drive by wire" throttle body, your foot pedal is not directly connected to the throttle body. Instead the foot pedal sends a varying electrical signal to the engine computer. The engine computer then commands the servo motor on the throttle body.
The problem with this system is you get NO "feed back" or "feel" of the throttle body plate sticking.
What is happening is the throttle plate is either not fully closing or it is not opening with in the time parameters. When this happens the computer commands the system to default to min idle.
This causes you to have an extremely low idle when stopped, backing up or moving from drive to reverse and into Park.
If you have a code reader, you can check the throttle plate positions.
Eventually as the plate sticks worse OR the plate does not close fully at idle you WILL get the dreaded "wrench" light.. It may flicker but once it lights up and stays on it WILL completely disable your go pedal and you will not be able to get engine above idle..
If you get the wrench light on, you can shut down the engine, then restart and the light will go out and the gas pedal will be restored.. But that is temporary at best.
PLEASE NOTE, ON A FORD THE WRENCH LIGHT DOES NOT SET CODES, PERIOD.
Only a CEL light will set codes.
You NEED to clean the throttle body NOW before you get the wrench.. Getting the wrench while driving will force you to the side of the road.
Why it happens?
Simply put, for what ever reason someone thought is would be a great idea to put the PCV connection directly below the throttle plate. In practice what happens is the PCV allows the manifold vacuum to pull the oily vapor from the crank case into the intake.. Great idea, but in this case a poor choice for location especially since the vapors can build up a very gummy residue which happens to be the throttle plate and body..
To clean, you will need to remove the filter box that sits on top of the throttle body.. once the filter box is off you will need some throttle body cleaner, some rags AND a helper.
You turn the key on to run position but don't start the engine.
You have your helper push the gas pedal to the floor (this opens the throttle plate).
Spray the throttle cleaner on a rag, carefully use the rag to wipe the walls of the throttle body clean of any tar like substance. Wipe the edges of the throttle plate while your at it.
You can spray the cleaner into the throttle body but if you do so you will need to allow time for all of the cleaner to evaporate before starting (depending on temps that could take 1/2 hr more). Otherwise it will act flooded.
Put it all back together and see if it runs better, it may take a few learning cycles before the computer gets the plate position figured out..
Being you also have 150K miles I would highly recommend changing at least your upstream O2 sensors (these are the ones located in front of the CAT CONVERTER). Upstream O2 sensors are the ones the computer uses to determine the fuel mixture. The downstream sensors are for emissions..
They are a "wear" item and typical mileage for them is about 80K miles, any mileage over that your are lucky. As they age they respond slower than they should, this results in the computer thinking the engine is running lean and adds too much fuel. This results in wasting fuel (bad fuel mileage) AND worse yet "poisoning" the cat converters!
Been there done that on BOTH items I mentioned.
