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  #1  
Old 11-18-2007, 01:56 PM
90 300SL
 
Join Date: Nov 2007
Posts: 6
Question 90 300sl Hard to start when temperature is 50 or bellow

I am rooky here and need some help. My 90 300sl is hard to start when parked overnight and temperature is bellow 50 degrees. It take me a few minutes to finally get it to iddle at very low rpm. If i press more gas it stalls. I have to let it warm up for a few minutes before i can drive it.
I have a non original o2 sensor on the car that I am replacing with an OEM in the next couple of days. will that make any difference? what ese to check?, temperature sensor? cold start injector? or pther?
Pls help...weather is getting colder and it is a real problem...

Thanks
Blablabloom
90 300sl
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  #2  
Old 11-18-2007, 05:09 PM
aam aam is offline
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Location: California
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Quote:
Originally Posted by Blablabloom View Post
I am rooky here and need some help. My 90 300sl is hard to start when parked overnight and temperature is bellow 50 degrees. It take me a few minutes to finally get it to iddle at very low rpm. If i press more gas it stalls. I have to let it warm up for a few minutes before i can drive it.
I have a non original o2 sensor on the car that I am replacing with an OEM in the next couple of days. will that make any difference? what ese to check?, temperature sensor? cold start injector? or pther?
Pls help...weather is getting colder and it is a real problem...

Thanks
Blablabloom
90 300sl
Check first for vacuum leaks.
2) Clean with carburetor cleaner the electronic idle speed control valve.
To test it pull the connector out, your rpm should jump to about 1500rpm.
If not thats your problem
I don't think is your sensor.
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  #3  
Old 11-18-2007, 05:13 PM
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Quote:
Originally Posted by Blablabloom View Post
I have a non original o2 sensor on the car that I am replacing with an OEM in the next couple of days. will that make any difference? what ese to check?, temperature sensor? cold start injector? or pther?
Your O2 sensor wouldn't have anything to do with it, your computer ignores it until it's up to operating temperature. I'd look at temperature sensors and your cold start injector.
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  #4  
Old 11-21-2007, 09:48 AM
90 300SL
 
Join Date: Nov 2007
Posts: 6
Smile

Thanks guys, i will check all of this this weekend and post the results...thanks again
Blablabloom
90 300SL
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  #5  
Old 11-21-2007, 11:22 AM
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Join Date: Apr 2000
Location: Falls Church, VA
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Sounds like the coolant temp sensor to me.
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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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  #6  
Old 11-26-2007, 10:05 PM
90 300SL
 
Join Date: Nov 2007
Posts: 6
Smile curent status

I have checked the idle speed control valve and disconnected the plug to it...no change in idle speed.
I have also discovered that the thermostat has been removed. The car takes forever to warm up and the temp guage barely reaches 80 degrees after driving for a while. I have checked the resistance reading on the coolant temp sensor and it was at 2.2kohm when the car was cold....55 degrees or so ambiant temperature. would the lack of thermostat create that issue or they are seperate? I am ordering a thermostat but should i order an idle speed valve too???

Thanks guys for all your input..much appreciated
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  #7  
Old 11-26-2007, 10:45 PM
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Originally Posted by Blablabloom View Post
I have also discovered that the thermostat has been removed. The car takes forever to warm up and the temp guage barely reaches 80 degrees after driving for a while.
Without a properly operating thermostat your car would be running cold most of the time. That will lead to excessive carbon buildup and all kinds of weird operation. My 75 had the thermostat gutted by some well-intentioned nitwit. After replacing it and driving the crap out of the car for a couple of weeks (long freeway drives at speeds the police would be unhappy with) most of the strangeness disappeared. After I took out the aux air valve and cleaned it, the rest of it cleared up.
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  #8  
Old 11-27-2007, 01:27 PM
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2.2k ohm sounds about right for 55 degrees, but check it with the engine warmed up, once you get a thermostat in it. Once you install the thermostat, you may see a great improvement since the FI control unit is currently very confused.

A new O2 sensor and a mixture adjustment via the on/off ratio is always a good idea.

Check to see if you are getting voltage to the ICV before replacing it. You check it by pulling the connector back just enough to get the meter's leads on the ICV's pins.
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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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  #9  
Old 11-27-2007, 06:24 PM
90 300SL
 
Join Date: Nov 2007
Posts: 6
Smile More checks and status

Thanks for the input Chuck and all of you guys too, FYI I have already replaced the O2 sensor a couple of weeks ago and that improved it a bit then. What kind of voltage should I get at the ICV valve? 12v constant or????
I think I am dealing with 2 different issues here. The thermostat is not going to prevent the car from starting, it should still start ok without it. What spark plugs are best for the 90 300sl? good old normal Bosch or can I use the bosch platinum + 2 that are in "fashion" now? I am also going to check/replace if needed the distrib. cap, rotor and plugs. and a new fuel filter. what do you think guys????? what is the best way to check the cold start injector to see if it is working? taking it out of the side of the distributor and see if it squirt while cranking or is there a safer way since we are dealing with fuel and electricity here???
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  #10  
Old 11-27-2007, 10:00 PM
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l don't have the 129 specs, but usually the idle relay sends between 3 and 4.5 volts to the valve. The higher the voltage, the more the relay is trying to slow the engine down. Be aware that a cheap repair for a bad relay or valve is to put a restrictor like a washer or dowel with a hole in it in the air path behind the valve. This cuts the air and slows the idle.

You can test your cold start injector by removing it, reconnecting the gas and electricity, sticking it in a jar, and cranking the starter. Do disconnect the coil so the engine won't start. You should get a small puff at 50 degrees.

The Bosch copper plugs are very hard to find. I have been using the Champion equivalent (N20-somethingY). Everyone seems to have poor luck with the platinums.
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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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  #11  
Old 11-27-2007, 10:36 PM
aam aam is offline
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Quote:
Originally Posted by Blablabloom View Post
Thanks for the input Chuck and all of you guys too, FYI I have already replaced the O2 sensor a couple of weeks ago and that improved it a bit then. What kind of voltage should I get at the ICV valve? 12v constant or????
I think I am dealing with 2 different issues here. The thermostat is not going to prevent the car from starting, it should still start ok without it. What spark plugs are best for the 90 300sl? good old normal Bosch or can I use the bosch platinum + 2 that are in "fashion" now? I am also going to check/replace if needed the distrib. cap, rotor and plugs. and a new fuel filter. what do you think guys????? what is the best way to check the cold start injector to see if it is working? taking it out of the side of the distributor and see if it squirt while cranking or is there a safer way since we are dealing with fuel and electricity here???
Your problem is the ICV.
Your Rpm didn't change.
Repair/replace.
1) Clean it, and push or twist.
2) 12 volts with key on # two.
3) If you want to test it, don't power it longer then one second
Don't burn it.
Should hear a clicking noise.

4) Install new thermostat.

5) Plugs, normal Bosch, replace every year.
Plug sticks to the head / damage the threads, expensive repair.
Platinum's they don't like contaminants.
On old engine don't last long.
6) I would not touch the cold start valve yet.
Regards,
aam.
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  #12  
Old 11-28-2007, 12:39 AM
90 300SL
 
Join Date: Nov 2007
Posts: 6
Thanks again guys, this is great info and at least I know where to start and what to look for...will keep you posted. If someone can tell me the exact champion plugs number this way i don't have to wonder if I got the right ones .....
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  #13  
Old 11-28-2007, 09:10 PM
aam aam is offline
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Posts: 115
Quote:
Originally Posted by Blablabloom View Post
Thanks again guys, this is great info and at least I know where to start and what to look for...will keep you posted. If someone can tell me the exact champion plugs number this way i don't have to wonder if I got the right ones .....
Here is a little more help Blablabloom.
www.********eaz.com
Has your Bosch plugs.$2.14
More info. on the idle control valve.
1) volts 11-14 operating.
2) 700 m. amps
3) Gets volts from the engine management module, but it is controlled by the temperature sensor.
Good hunting.
Regards,
aam.
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  #14  
Old 11-29-2007, 08:40 PM
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Join Date: Oct 2002
Location: Columbus, Ohio
Posts: 155
I went through a period with my 91 300SL with stalling and poor idling and the chased all of the usual fuels system issues. The problem was solved with a new ignition coil. Used regular NGK plugs. I would also suggest new rotor and distributor cap. This engine seems to need a very good spark from a sound ignition system and should be checked before all of the fuel system stuff.

Hope this helps.

sldan
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  #15  
Old 12-03-2007, 10:56 PM
90 300SL
 
Join Date: Nov 2007
Posts: 6
thanks guys, I have ordered all the electrical ignition components and will replace them by the weekend, Also a new thermostat, and cleaned all 3 water sensors, new coolant etc... will keep you posted....
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