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Old 07-10-2007, 01:53 PM
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Join Date: Jul 2007
Posts: 3
'88 560sl Idle Issues

First of all, thanks for this forum, seems to be quite a good resource for Mercedes owners!

I'll try to make this short as possible but the issue/s have been long in solving... Long story short, my lady friend found her "dream" car while on a trip with her long time buddy... against my (on the phone) advice, she bought it and had her very pretty 1988 black 560sl shipped out west from Hot Springs Arkansas where she found it..

When it came off the truck, it was immediately apparant to me that, despite the car looking quite perfect, and only 80k on the odo, it had some issues! (understatement)

Back to cutting to the chase.. over $6,000. later, we've gotten the stearing box/rack and pump resealed (did not even know that was one of the problems!) the differential mounts replaced, the rear axles replaced... tuneup, flushes, etc. etc...

The car still idled rough so a trip back to the shop had them replacing the idle control valve... seemed to run a *bit* better but, here's the problem...

About half the time, the compensation for the AC that would, if the AC didn't kick on, take the RPM up to about 1500, does just that.. It will suddenly race up to 1500 all on its own.. While watching it, it happened once just as the AC clutch disengaged, and once again completely independent of the AC operation..

Shope we've been dealing with is willing to put on a control unit (electric) to diagnose problem for free.. issue I have, after picking up the car and having the steering extremely loose and having the shop take the "I didn't notice that when I drove it" response line.. and adopt pretty much the same attitude about each other problem I related to them after repair.. I'm not sure I trust taking it back to them again, regardless of the "diagnos for free" statement!

I'm reasonably good at engine work, I don't necessariy enjoy it, which is why we just paid over seven grand to have someone else do this stuff...

Anyway.. any ideas on what to try to attempt to narrow down what's going on? The compensation valve is new... what to try next?

Thanks MUCH in advance!

Wayne
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Old 07-10-2007, 09:54 PM
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Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
When you get a sudden idle jump like that, it is usually that the electronic idle control has stopped sending power to the idle control valve, allowing the valve to go fully open and allow a bunch of air through, thus raising the RPM.

This can be caused by the idle controller losing it, or by a loss of power supplied to the idle controller by the over voltage protection (OVP) relay, Another but more remote cause is a vacuum leak, which allows "false air" into the injection system at random times.

I guess if I spent a bunch of money resealing the steering box and the car still had uncertain steering, I would ask the shop why they didn't install a rebuilt box instead of resealing the old one. And if they didn't have a good answer, I would take my car somewhere else.

Anyway, try a search. Lots of posts on the idle and OVP problem.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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Old 07-10-2007, 10:44 PM
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Join Date: Jul 2007
Posts: 3
Quote:
Originally Posted by ctaylor738 View Post
When you get a sudden idle jump like that, it is usually that the electronic idle control has stopped sending power to the idle control valve, allowing the valve to go fully open and allow a bunch of air through, thus raising the RPM.

This can be caused by the idle controller losing it, or by a loss of power supplied to the idle controller by the over voltage protection (OVP) relay, Another but more remote cause is a vacuum leak, which allows "false air" into the injection system at random times.

I guess if I spent a bunch of money resealing the steering box and the car still had uncertain steering, I would ask the shop why they didn't install a rebuilt box instead of resealing the old one. And if they didn't have a good answer, I would take my car somewhere else.

Anyway, try a search. Lots of posts on the idle and OVP problem.
Thanks for the response! Since posting my question, I've researched this forum and man... this is a GREAT resource!

On the steering, I talked with the wrench who did the repair and he was simply leery of going "too tight" and since we keep the car two hours from the shop, it was a two hour drive for my lady, who was scared to death while driving it..

Mistake?

YOU BET!

Steering is now fixed (very simple play adjustment) Idle valve has been replaced at $600.+ I see we can get them here for just over $200!..

Spoke with the "kid" (thirty something) today who manages the shop where we took it initially.. .and secondairly... I'd been giving them the benefit of the doubt but his answer to me "well it's a 20 year old car" when I gave him a bit of diagnosis tip about the idle running away got my goat!

I'm gonna let him "put in an idle controler" for free for test purposes, but I don't think I'm going to be really inclined to pay him for it!

Did I mention this site was a GREAT resource!!!!!!!!!!!!!

Wayne
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