1990 560 SEL idle surges - PeachParts Mercedes-Benz Forum

whogault · #1 09-11-2006, 10:54 AM

My SEL will surge intermitantly from normal idle to anywhere from 1200 to 1700 rpm. This can be quite disconcerting when you are trying to slowly back up, or take your foot off the brake at a stop light. Any "usual suspects" I should look at? Also, a two for one question. Sometimes, but not always, and under many different temp. conditions and driving situations, my tranny won't up-shift into 4th gear. My MB shop has told me they "lubed the cable" and the second time, they "tightened it" Still happening. Any ideas?

Snibble · #2 09-11-2006, 01:23 PM

Is your idle in the 1200 range? Is this when its in P or D?

A good idle should be in the 650 range

whogault · #3 09-11-2006, 01:30 PM

Yes- it has normal idle most of the time. Then, it surges for about 3 seconds and comes down.

david s poole · #4 09-11-2006, 04:17 PM

controlled by relay in pass floor under panel[where feet go] and guess what supplies power to this control unit!!!!!your friend and mine the ovp relay

whogault · #5 09-11-2006, 04:22 PM

Did I miss the begining of your post? Seemed to have gotten you in mid sentence.....

david s poole · #6 09-11-2006, 04:38 PM

ooops silly me i assumed[there's that word again]that you knew about the automatic idle valve on the engine and this is controlled by the large relay under passengers feet.this is more common than the valve itself.other thing is the overvoltage protection relay which supplies pwr to the idle valve control unit.this relay is under the hood not far from the brake booster,next to two other bigger relays in front of windshield.my gut feeling is the idle speed control unit because if the ovp you should get at least one other lite pop up on instrument panel.

whogault · #7 09-11-2006, 04:54 PM

So when I drop it off at my local Indy to have the rebuilt cylindar head put on( another longer story) should I tell them to just replace this relay? When I complained to them before about the surging, they told me (twice) that it didn't do it for them so they could not diagnose. It is intermitant, after all! Also- got any ideas on the intermitant failure to upshift to 4th?

david s poole · #8 09-11-2006, 05:12 PM

if this is the 560sel trans you are asking about,intermittent no shift to 4th is possibly 1 of 2 things. bad valve body or too much dirt in the little filter screens that protect the govenor.if you run up the rpm's and back your foot off the throttle in 3rd will it shift to 4th?

whogault · #9 09-11-2006, 05:55 PM

No- not really. Most times is just upshifts after a while. Sometimes it shifts just fine. Sometimes it really clunks up to fourth, and sometimes it hangs in third for a while.

david s poole · #10 09-11-2006, 06:13 PM

then items 1and 2 apply.