car wont die easy troubleshooting? - PeachParts Mercedes-Benz Forum

argus445 · #1 12-16-2008, 05:44 PM

Got home from work today go turn off the car it keeps running at about 400rpm about 1/2 what idle was with key on i'm figuring eather vacuum pump or the plunger on the injector pump has a leak easiest way to pinpoint the problem would be ??

vwnate1 · #2 12-16-2008, 05:52 PM

As the key on makes it idle faster there's prolly a leak in the central locking or the HVAC systems , try turning them off and see if the engine doesn't slow down and stop .

My 300CD has a leaky locking chamber in the passenger side door so if the doors are locked , the engine won't quite stop , it'll idle down to 300 RPM's but not stop unless I unlock the door then after a few moments it'll Stop running .

You are the on site detective to take your time and figure it out

.

If you look under the hood , the yellow plastic pipes feed the central locking so cap them off and if it now stops , VIOLA ! you've found it .

The green pipes feed the HVAC system .

so on and so forth .

Once in a while the two short rubber hoses connecting the brown plastic shutoff pipes to the back of the ignition switch get all oil soaked and blubbery , leak enough vacuum to prevent shutoff .

ALWAYS use new rubber hose bits ! never , _EVER_ trip the loose end off one and re-connect it .

Biodiesel300TD · #3 12-16-2008, 05:53 PM

You need a mity vac. It's hand vac pump. With this you can test wether it's the pump or the shut-off valve. You could also have a leak in your climate control system and/or door lock system as well. A leak on just about any vac system in the car affects all the others.

argus445 · #4 12-16-2008, 06:09 PM

I have the door locks isolated too many leaks there to begin with. I figured there was one hose u could hook to and pull a vacuum and check the switch and the shutoff plunger i'm hoping it's just a cracked hose or something nothing major

vwnate1 · #5 12-16-2008, 06:16 PM

Yes , there's TWO brown plastic hoses , one goes from the vacuum manifold to the keyswitch and the other goes from the keyswitch to the IP's shut off diaphram ~ before anything else , check all four of the 3" brubber hose bits connecting these , two under the dash , two under the hood .

FWIW , Harbor Freight sells the Vity-Vac cheaper than anyone else .

There's also a blue vacuum resivoir pipe under the hood , cap that off for testing , some years have a black with yellow tracer pipe for the cruise control .

argus445 · #6 12-17-2008, 06:25 PM

Dug into it today no leaks from the shutoff back to the main vaccum line leading into the break boosters i'm getting about 8" at idle and about 15-20 at 2500-3000 rpm i'm wondering how much vaccum should be at idle at the branch from main vaccum line going into brake booster and where all the other lines fit in is? i'm wondering if my vacuum pumps weak or if i have a leak i can take the lines off of the main system acc/doorlocks/shutoff switch inside and it holds 20+ " vaccum so something else is eather bleeding off or my vacumm pumps weak

toomany MBZ · #7 12-17-2008, 06:51 PM

I recommend taking the door locks out of the equation. Block off the yellow check valve.
This is the most popular solution.
I have used a mity-vac on the shut off valve, tested fine. Turned out that was still the culprit, as you might think, that took a while!
Check for oil in the brown line between the ignition switch, and shut off valve.

vwnate1 · #8 12-17-2008, 09:41 PM

Else it'd stay up @ 20" vacuum all the time .

Now , go find the leak and cap it off , be happy .

argus445 · #9 12-18-2008, 04:40 PM

your joking right? 25 yr old car i doubt anything that doesnt leak i just curious how much it should have seems like 20 is good # it gets that above idle not sure if at idle it's suppose to or not. the ip circuit doesnt have a leak