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I am proficient in my ML63 and S600. However, I am helping a friend fix his SL500. It is a beautiful car, 78K miles, it drives great but has a couple of issues.

1. occasionally, the fans don't come on and neither does the AC when this happens. There is a brand new radiator. When the AC operates, the two fans do come on. The mail cooling fan operates correctly. I have also caught it not engaging the starter at the same time that the other issue occurs. This makes me think that there is a grounding point issue. Do you folks know where any common grounding point might be in the front? Or, any other words of wisdom? When the problem occurs, it is nice and cool on the highway and then goes to 110 when sitting in traffic.

2. I have fixed vacuum leaks yet it idles poorly when first started. Occasionally, it is also slightly hesitant when beginning to drive again after stopping. The O2 sensors are original. O2 sensors and/or MAF sensor or?
 

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1999 ML320, 1998 SL500
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I am so lucky to have bought a 1998 SL500 at 77,000 miles and now at around 110,000. It has had it's ration of issues, PS Pump, front strut, steering linkages, plugs and coils, etc., but never any mystery issue related to vacuum or bad wiring.

Not to say anything about this forum, but it wouldn't exist if the MB cars didn't have serious over-complicated systems and plastics and rubber that fail with time and heat. Before I "snapped up" the SL I had gone through 4 Corvettes, all new, but there was never a requirement to do any repair on any of them except the last one that was trapped in the middle of a 5-6 car pileup. The Vette was the only one that cold drive away and it had a complete rebuild after the event. DuPont even came to SD to supervise the paint job. I won't post pictures of the rebuild on this forum but it was taken down to the bare bones and restored to new condition.

On the other side of the MB issues, my wife has a 1999 ML320, bought new, and now at around 70,000 miles. It's had the usual transmission adapter issues and still has an uncomfortable idle. Other than that it seems to be holding up fine. Her car was made in the USA, my SL was built in Germany. I doubt that makes any difference but it's sort of interesting.
 

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94 SL320 98 SL500 99 SL600
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Clean and sand fuse connectors. Check brown wires that are screwed to body for loose or corroded. Cables at starter and battery. MAF and air temp sensor did this on my 94 SL320.
 

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I am proficient in my ML63 and S600. However, I am helping a friend fix his SL500. It is a beautiful car, 78K miles, it drives great but has a couple of issues.

1. occasionally, the fans don't come on and neither does the AC when this happens. There is a brand new radiator. When the AC operates, the two fans do come on. The mail cooling fan operates correctly. I have also caught it not engaging the starter at the same time that the other issue occurs. This makes me think that there is a grounding point issue. Do you folks know where any common grounding point might be in the front? Or, any other words of wisdom? When the problem occurs, it is nice and cool on the highway and then goes to 110 when sitting in traffic.

2. I have fixed vacuum leaks yet it idles poorly when first started. Occasionally, it is also slightly hesitant when beginning to drive again after stopping. The O2 sensors are original. O2 sensors and/or MAF sensor or?
I had the same problem it was the 4 prong temp sensor that controls the aux fan and cold start. It affects the idle and cooling.
 

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If you have been around more seasoned Mercedes Benz you have most likely previously found out about the issue with breaking down protection on the motor wiring bridles during the ahead of schedule to mid 1990's. Kent will show you a genuine case of the issue and how to rapidly spot inconvenience.
Tutuapp 9apps Showbox
 
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