rough idle - PeachParts Mercedes-Benz Forum

brownrice78 · #1 03-13-2016, 07:18 PM

Hey guys. Need your help. Car has a nasty shake at idle that I can't seem to figure out. I noticed it now in the warmer weather. Car idles great when cold but the entire car shakes side to side when warm and at idle.

New engine mounts. Recent valve adjustment. New fuel filters. I bought the gold damper screw. Didn't change a thing.

Can an air leak cause this? Best way to check to see if the injectors are the problem?

bsmuwk · #2 03-13-2016, 08:17 PM

Quote:

Originally Posted by brownrice78

Hey guys. Need your help. Car has a nasty shake at idle that I can't seem to figure out. I noticed it now in the warmer weather. Car idles great when cold but the entire car shakes side to side when warm and at idle.

New engine mounts. Recent valve adjustment. New fuel filters. I bought the gold damper screw. Didn't change a thing.

Can an air leak cause this? Best way to check to see if the injectors are the problem?

With the engine running warm and doing it's shake, you can crack an injector line open one by one to isolate cylinders (if that's any sort of cause) - otherwise your only injector related option is to remove them entirely and send them to someone who can pop test them/service them.

Have your engine damper shocks and their associated mounts/bushings ever been serviced? Where's your idle speed set?

brownrice78 · #3 03-13-2016, 08:47 PM

I played a little bit with the idle speed and set it higher. Didn't help much. I'm thinking if it was injector related then it would show up cold also? I'll try to cracked the lines. Good idea

cho · #4 03-14-2016, 06:55 AM

Quote:

Originally Posted by brownrice78

Car idles great when cold but the entire car shakes side to side when warm and at idle.

I notice this behavior after long highway run and sudden stop (say traffic light...) my car was shaking like mad cow.

after lots of r&r,.. adjustments etc..it turned to be delivery valves (IP).
easy swap ... hard to find parts....in Europe dv per piece was 20 usd...

lets hope that you have some air in fuel hose issue

.

superapan · #5 03-14-2016, 08:37 AM

I have the exact same problem. Super smooth when cold, rocks side to side when warm. I usually put it in neutral (higher RPM) at traffic lights, which helps a bit. I got valve adjustment, diesel purge and rack damper bolt replacement on my todo list...

mytimeyet · #6 03-14-2016, 10:35 AM

Somewhat the same problem but I also had some slight weeping on the return lines @ the injectors. When I recently replaced the return lines the idle improved quite a lot! Yet another possible place to poke at.

brownrice78 · #7 03-14-2016, 02:03 PM

Quote:

Originally Posted by mytimeyet

Somewhat the same problem but I also had some slight weeping on the return lines @ the injectors. When I recently replaced the return lines the idle improved quite a lot! Yet another possible place to poke at.

Interesting. I thought the return lines are not under pressure but I might be wrong

oilslick · #8 03-14-2016, 02:38 PM

Quote:

Originally Posted by brownrice78

Interesting. I thought the return lines are not under pressure but I might be wrong

They are not under pressure.

Adriel · #9 03-14-2016, 04:08 PM

Quote:

Originally Posted by cho

I notice this behavior after long highway run and sudden stop (say traffic light...) my car was shaking like mad cow.

after lots of r&r,.. adjustments etc..it turned to be delivery valves (IP).
easy swap ... hard to find parts....in Europe dv per piece was 20 usd...

lets hope that you have some air in fuel hose issue

.

Replaced the bad injector, engine still shakes bad and runs like not firing on all cylinders also. Did everything but the delivery valves. My delivery valves are leaking, especially number one is pouring out fuel. Was going to just re-seal.

What was involved in R and Ring the delivery valves? Thought a shop had to set it up?

Thank you in advance for any help!

cho · #10 03-15-2016, 06:48 AM

hi mate

r and r of DV's?... nothing special
be sure to acquire new delivery valve washers
take the old ones out and plunge in new ones.

I did it one by one,.. didnt like the idea of mixing springs and valve holders...
take the air out of metal fuel lines afterwards....

search through my old post so you can find proper PN's for valves and washers.

edit: shop is needed if you mess with elements ..so be careful not to touch them (two nuts besides each DV holder)

cheers

brownrice78 · #11 03-17-2016, 01:45 PM

Ok. Reporting back. I changed out the rubber fuel hoses before and after the plastic inline filter with 5/16 fuel hose from the local autozone. Definitely an improvement!! Before the car was shaking so bad that I couldn't adjust the rack damper screw with the car running. The car still has a shake but it's not so violent.

I did notice that my engine shocks have issues. One is not working at all and the other one has bad bushings. Do the engine shocks play a key role in controlling the engine idle shake and also can I use the old shock mounts with new shocks?

cho · #12 03-18-2016, 05:22 AM

Quote:

Originally Posted by brownrice78

Do the engine shocks play a key role in controlling the engine idle shake and also can I use the old shock mounts with new shocks?

no they don't,yes you can

.

barry12345 · #13 03-18-2016, 12:43 PM

Quote:

Originally Posted by oilslick

They are not under pressure.

If you really did notice some difference and it was certain. I might remove the fuel cap and blow out the return line. I can think of no reason this could be an issue but at the same time nothing would be harmed.

Someone else may have an opinion of why a leaky return line would cause any improvement in idle once replaced. All I think is repairing something that seems unrelated should not have changed anything. If everything else was good.

Also as one member mentions many times. It is an excellent ideal to put a clear hose in the system past the relief valve. This to make sure there is no visable air. Air will be more problematic at idle.

I am not suggesting the above mentioned items are the issue and I could easily be missing something in relation to the return hose leaking and being replaced. It just seemed strange to me that the effect you observed if real should have happened.

Also having leaky delivery valves will affect injector performance. I think you know this.

funola · #14 03-18-2016, 12:55 PM

There is low pressure in the return lines from pushing fuel back to the tank through a long and small diameter line. I estimate 1 to 3 psi if everything is normal (no clogs back to tank). If there is leaks in the injector daisy lines, air can get into the pump via the orifice in the banjo bolt when it drains down when engine is off. Air may also get in via the orifice while running due to the pulsation of the lift pump.

Quote:

Originally Posted by barry12345

If you really did notice some difference and it was certain. I might remove the fuel cap and blow out the return line. I can think of no reason this could be an issue but at the same time nothing would be harmed.

Someone else may have an opinion of why a leaky return line would cause any improvement in idle once replaced. All I think is repairing something that seems unrelated should not have changed anything. If everything else was good.

Also as one member mentions many times. It is an excellent ideal to put a clear hose in the system past the relief valve. This to make sure there is no visable air. Air will be more problematic at idle.

I am not suggesting the above mentioned items are the issue and I could easily be missing something in relation to the return hose leaking and being replaced. It just seemed strange to me that the effect you observed if real should have happened.