Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help




Go Back   PeachParts Mercedes ShopForum > Technical Information and Support > Tech Help

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 11-01-2002, 12:37 PM
Mateo
Guest
 
Posts: n/a
Reving 300 E at idle?

my 87 300 E started reving at iddle yesterday. It reves back and forth as if someone was pushing on the accelerator and letting off every couple of seconds. What could possibly cause this. I recently gave it new plugs (which I do every 3000 miles because of oil fouling due to leaky valve guides). I put in my normal bosch suppers, and gave her an oil change. I've had nothing but problems since. Help please.

Danka.
Reply With Quote
  #2  
Old 11-01-2002, 12:51 PM
Moderator
 
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
The most basic answer is that the amount of air entering the motor is changing. This can be caused by air leaks or by irratic electronic control of the idle air valve.
__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
Reply With Quote
  #3  
Old 11-01-2002, 01:23 PM
Moderator
 
Join Date: Dec 2001
Location: Southern California, U.S.A.
Posts: 8,508
My engine developed the same problem a while ago.

My mechanic replaced the mass air sensor, and it didn't fix the problem.

My mechanic then replaced the throttle actuator (you car doesn't have a throttle actuator. You have an idle control valve). It didn't fix the problem

The mechanic gave up and told me to take it to the dealer.

They immediately diagnosed the problem as a leak at the intake manifold gasket. $400 later, the car was fixed.

Needless to say, I now have a new mechanic.
__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
Reply With Quote
  #4  
Old 11-01-2002, 01:59 PM
Registered User
 
Join Date: Aug 2001
Location: secret
Posts: 3,044
Quote:
Originally posted by suginami
My engine developed the same problem a while ago.

They immediately diagnosed the problem as a leak at the intake manifold gasket.
Just out of curiosity, how did a leaky manifold make the engine rev up and down??
Reply With Quote
  #5  
Old 11-01-2002, 02:06 PM
Moderator
 
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
False air! Engine speed is solely determined by air flow quantity.
__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
Reply With Quote
  #6  
Old 11-01-2002, 02:54 PM
Registered User
 
Join Date: Aug 2001
Location: secret
Posts: 3,044
Wouldn't that raise the idle and sustain it at a higher RPM??
Reply With Quote
  #7  
Old 11-01-2002, 05:41 PM
Mateo
Guest
 
Posts: n/a
thanks for all the responces...

I now have a good idea where to start anyway (I hope it's not the intake manifold gasket). Granted I only payed $2K for the car a year ago, it's been good to me. I could pay out more than I payed for the car to fix some problem, valve guides etc, but I wont. So hopefully the problem is something I can fix myself in a short amount of time, while not spending loads of $$$$$

Thanks again.
Reply With Quote
  #8  
Old 11-01-2002, 07:56 PM
Moderator
 
Join Date: Dec 2001
Location: Southern California, U.S.A.
Posts: 8,508
I wouldn't limit yourself to the intake manifold seal.

You can have a vacuum leak anywhere.

Further, it really could be the mass air sensor. I've read from technicians here (maybe even Stevebfl) that it's impossible to diagnose a bad mass air sensor. The only way to check is to take out the old one and put in a new one.

FWIW, they are about $225-$250, and you can install one in 15 minutes. On my car (different engine, 3.2 liter M104), it's in the big, fat plastic hose next to the air cleaner.

It could also be the idle control valve. I'm sure a real technician could diagnose whether you have a vacuum leak or a parts failure. If you have no diagnostic tools, you could always trouble shoot the problem yourself by throwing parts at it until you replace the right part, but then again, that could be expensive.

You can check for a leak at the intake manifold seal by spraying water at the gasket with the engine running. It will bubble if there's a leak. You can also check for hoses that are cracked or came unattached.
__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
Reply With Quote
  #9  
Old 11-01-2002, 08:23 PM
Registered User
 
Join Date: Oct 2002
Location: NYC, USA
Posts: 27
I had a similar experience where the idle of my 190E varied between 500-1500 RPM's continuously. It turned out to be the idle control solenoid
Reply With Quote
  #10  
Old 11-02-2002, 12:48 PM
Mateo
Guest
 
Posts: n/a
Bizzar

Bizzar - when I got home yesterday it was up to it's new tricks by reaving, it had no rhyme or reason to when it would rev, and when it would idle at normal speed. I started looking for leaks and figeting around with things until it started to sustain the higher reving speed, only to calm down and get back to it's original idle speed. Strange. I let the car idle for a while and it didn't revert back. I doubt the problem fixed itself, but I'm hoping it did **Thumbs crossed**
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 06:43 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2011 Pelican Parts - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page