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Premium Member
1988 300 SE
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47 Posts
Discussion Starter #1
[?]Ruff Engine Idle

Hello fellow members,

Got another question for you, This may be easy for you veterans. Before I start to dig into a lot of replacing parts I will see if I can tap your brains…

I have a ’88 300 SE with 230,000 miles on it. In the mornings or even when it sits for a while, when I start it, the engine will run ruff for about 30 to 60 seconds. Then it seems to line out and run great. I don’t have problems with accelerating, normal driving, or curb idle. Just when I star the car. It is more so in the morning than during the day. I try to turn the key and wait until the buzzer quits (just used as a timer) then start the car. It seems to help. Makes me think that I am loosing fuel pressure in the lines…don’t know… Any Ideas before I start replacing everything?
 

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1991 300 SE
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18,534 Posts
If there were a problem with the primary pressure regulator I would think it would be constant regardless of engine condition. There could be a problem with the cold start valve or the temp sensor that provides engine temp info to the ECU which controls the CSV. You may be right about waiting for the buzzer to go off in that full system pressurization may help with cold start but if the CSV or temp sensor are not working correctly the engine will still run rough. With those miles and from what you describe, it could also be worn or leaking injectors. They may need to be replaced or resealed so there is no leaking air around the seals.
 

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Depends on the day!
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13,337 Posts
Injectors if they have not been done are Most definetly worn out which I'm sure is contributing to your problem. I also see bad fuel pressure regulators cause some similar issues. I would also check your cold start valve. Pull the valve on the next cold morning and see if it fires when you turn the car over. If not, either the sensor (most likely) or the valve is not fucntioning.


You might also try pulling your air idle valve and giving it a clean...it might be slow to react in the morning...

Jonathan
 

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1982 300TD
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163 Posts
My '86 560 SEC was doing that exact same thing. I replaced the injectors, (112,000 miles) the injector inserts, and the o-rings. End of problem.



Best Regards,


e
 
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