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1987 420 SEL
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30 Posts
Discussion Starter #1
I have a 1987 420 SEL and when i first start it, it idles around 1500 rpm, and fluctuates up and down a bit, but as soon as i put it into a drive gear, it drops back down. Anybody that has a problem like this before could let me know what it could be, I would be very thankfull.
 

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88,560 SEC & SEL Euros, 06 S-500, 06 SRT8 Magnum
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246 Posts
Most likly the OVP relay causes this? Best to pop in a new one, or you could take the old one apart and soder the board.

MBGary
 

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Yes, this has happened to me before on my 86' 420 SEL
I'm guessing your car jumps a little when you put it into drive or reverse, so you'll have to probably get the vacuum adjusted somewhere. But it's most likely the idle control unit that you will have to replace. I hope this helps.
 

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As mentioned above by Gary and Saleen, it could either OVP relay (especially if ABS light illuminates), or idle control relay, or idle control valve.

Also, do not rule out :

- vacuum leak at injector seals
- vacuum leak at bypass pipe on idle air valve

Although, your idle comes down when you select gear, it's probably not low enough. The V8's should idle @ 550rpm +/- 50 in 'P' or 'N' and 500rpm in 'D' or 'R'.

So gear selection should occur at approx 600rpm - not 1500 rpm, which will be painful for the tranny. I'd look at resolving this asap.
 

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1991 300 SE
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Try cleaning the ICV in brake or carb cleaner first, about 24 hours. There may also be a problem with the throttle position switch, check for worn or loose wires or broken terminals.
 

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2016 E400 4Matic Sedan
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do a search using my id and high idle. You should be able to permnently resolve the high idle isse with zero cost and worries.
 

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1987 420 SEL
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Discussion Starter #7
Thanks to everyone for the input. My car does jump a little bit goin into a drive gear. The ABS light also comes on. (i was told the ABS needs to be looked at) I'm goin to try to look at it today because rain all week was no good for servicing a car. More as it comes along.
 

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1991 300 SE
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NewMBie - 5/13/2005 10:57 PM

do a search using my id and high idle. You should be able to permnently resolve the high idle isse with zero cost and worries.
Although your post is meant to be cynical and mocking, if he researched your experience his problem will be solved.

My high idle problem was fixed with a new ICV. His high idle problem will be fixed when he replaces the OVP relay. Everyone has his high idle problem fixed but you. Your car was either built by Satan or built during Oktoberfest and Uwe had a bad hangover when installing your fueling system.
 

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jdc1244a - 5/14/2005 1:10 PM
Everyone has his high idle problem fixed but you. Your car was either built by Satan or built during Oktoberfest and Uwe had a bad hangover when installing your fueling system.
Tell me about it. As you know, I went throught everything there is about high idle and could not fix that system. That is also why I am leaving this "hard start" issue alone. Two cranks per start isn't that bad. Somehow I knew if I spend time and $ on it, I would probably get the same result as high idle.

Hopefully my FPR story ends here.
 

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1988 560SEL sold:
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jdc1244a - 5/14/2005 1:10 PM
Your car was either built by Satan or built during Oktoberfest and Uwe had a bad hangover when installing your fueling system.
LOL, I think it may have been built the day after West Germany won the World Cup in 1990 (I'm serious about this - I was there, in Frankfurt the day after they won and the City was the site of the team's victory parade). The euphoria that has been building up since the fall of Berlin Wall previous autumn reached a high point on that day, and only people who managed to work that day in Germany were the Americans who could care less about soccer. For that reason, I am a little wary of '91 models.

FYI, my car's idle is a consistent 550 at D but when in P and N fully warmed up, it's 750 which is still a little higher than the optimum.
 

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If idle is 750 in 'P' at normal operating temp, it is likely due to the idle control valve slide gate not closing fully. Not an issue yet I guess, but it may deteriorate.
 

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'88 500 SEL
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Hi to all. I have the same problem: I have buyed a '88 500 SEL, the idle is high in park and neutral (1400/1500 rpm) and the ABS lamp is on: sorry, but what is the OVP Relay? I'm Italian and don't understand the acronym OVP. Many thanks and sorry for my bad English... Gianfranco
 

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84 300D; 85 380SE
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jdc -- if you're still following this thread, after
cleaning the ICV in carb cleaner, do you lube the
valve? if so, what's a suitable lube? I saw one
post that actually said WD-40, but I can't see that
helping to any great degree. anyone else?
 

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1991 300 SE
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Gianfranco - 5/31/2005 2:41 PM

Hi to all. I have the same problem: I have buyed a '88 500 SEL, the idle is high in park and neutral (1400/1500 rpm) and the ABS lamp is on: sorry, but what is the OVP Relay? I'm Italian and don't understand the acronym OVP. Many thanks and sorry for my bad English... Gianfranco
Over Voltage Protection relay – it provides consistent power to the ECU allowing the ECU to accurately monitor the fuel system sensors. If your ABS light is on there’s a good chance the relay is bad.

rayroyw - 5/31/2005 8:31 PM

jdc -- if you're still following this thread, after
cleaning the ICV in carb cleaner, do you lube the
valve? if so, what's a suitable lube? I saw one
post that actually said WD-40, but I can't see that
helping to any great degree. anyone else?
No, the idea is to get the valve mechanism clean and dirt free so it will operate smoothly.
 

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88,560 SEC & SEL Euros, 06 S-500, 06 SRT8 Magnum
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Franco

The OVP Relay is located between the firewall and the engine area causes these high idle problems I attached a photo of the unit replace it and this will resolve your problems. Question: what area of Italia are you located post some photos of your SEL.

MBGary

[email protected]
 

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'88 500 SEL
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Ehi, many thanks to all, next week i try this solution... And for MBGary, I live in Bergamo (north Italy), city located at 40 km. from Milan and 200 km. from Venice... For the photos, if you wanna I can send them now, but the car has works to make, otherwise I send to them when it is all ok... One question: where I can send photos? : -)

Gianfranco
 

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88,560 SEC & SEL Euros, 06 S-500, 06 SRT8 Magnum
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Gianfranco

E-mail just click on my thread photo and go to my e-mail address. Better still [email protected]
PS: my son-in-law was born in Italia not sure of the exact location. I have travelled through from the north to Capri just a beautiful country. Crazy drivers though!! My favorite breakfast was denci and eggs, forget the rolls (hockey pucks) use those for tennis balls? attached my 2 babies.

MBGary
 

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