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500SE AMG, E350 4matic, GL 450
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Discussion Starter #1
Here are all the issues I plan of working on the 90 300SEL. Any suggestions as to how to fix/replace would be appeciated:
1. No heat. I replaced the thermostat. If I let it sit for 20 minutes the heat starts, but turns cold again.
2. Hard start in the mornings-summer or winter. I have to pump the gas pedal and then try and try before it starts. I sprayed out the throttle body. This seemed to help a little bit, but still have the problem.
3. Sometimes at lights, it starts to almost "bounce"......hard to describe. Seems like it wants to shut off. When I get moving again, it does this sputtering take-off thing. This doesn't happen all the time, but it if I have been driving for 30 minutes to an hour or so, it does.
Any suggestions would be appeciated.
Mike Pillay[:)]
 

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1987 420 SEL
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2,095 Posts
For your heat, I would check the monovalve. Also, when is the last time that your coolant was flushed and refilled?

For the hard starts, try some Lubro Moly Jectron fuel injection cleaner and the Ventil Sauber valve cleaner. Here's a link:

https://www.autohausaz.com/membersonly/lookup_parts.cfm?SubcategoryID=2222&CFID=548340&CFTOKEN=67577146

I had a hard starting problem myself and my mechanic bought me some of this to use. Now I just tried it yesterday and my MB has been starting much easier and cleaner. Matter of fact, this morning I gave the 420 a good blow out on the highway.

For the sputtering. When is the last time you checked your spark plugs or had a tune up? Also, check your plug wires and connectors. Hopefully this helps you. Have a good day!
 

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88,560 SEC & SEL Euros, 06 S-500, 06 SRT8 Magnum
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246 Posts
Michael

Have you checked the 20 cent fuse on the top of the OVP relay do a search on the forum this may be your problem shows you the location and what is used for.

Gary
 

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500SE AMG, E350 4matic, GL 450
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5,901 Posts
Discussion Starter #4
Plugs and wires were replaced this summer. I had the problem before and it had little effect. This may sound dumb, but besides plugs and wires what else is done for a tune up???? I have not checked the fuse, but I will ASAP. Could this be something as simple as a fuel filter?
 

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1987 420 SEL
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2,095 Posts
Start with the small inexpensive things first to begin diagnosing your problem.
 

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Depends on the day!
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13,337 Posts
A good cap and rotor are key as well. How many miles on the car? Pumping the gas pedal only introduces extra air, not fuel. Sounds like your injectors might be leaking down quite badly. If you park the car and try to start it a minute or two later will it fire up easily?

Jonathan
 

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500SE AMG, E350 4matic, GL 450
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5,901 Posts
Discussion Starter #7
175,000 miles on the car. Once it starts, if I shut it off and wait a minute or two, it will start right up.
 

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1991 300 SE
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18,534 Posts
1. Sounds like your aux water pump is out.
2 and three are the same, I think – work through the list below to eliminate the most common causes:

The EHA/Fuel Distributor may be dirty, leaking, or not getting current:

http://www.thebenzbin.com/mercedes-gas-smell.html

Bad Distributor Cap and Rotor.
Vacuum Hoses cracked or leaking.
Faulty CIS Coolant Temperature Sensor.
Failed OVP Relay
Sticking Idle Control Valve.
Dirty Throttle Body.
Failed O2 Sensor.
 

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4,717 Posts
All good advices are given already, so I have nothing special to add. For 2&3, I'd reemphasize bad distributor caps and rotor. Also, if you have service records from previous owner(s), check to see if the fuel injectors have been serviced/changed recently.
 
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