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Old 05-30-2002, 09:49 AM
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Join Date: May 2002
Posts: 27
560SEL hard start /low rough idle

Have been struggling with this prob as follows:
-After sitting overnight at about 60 deg F ambient cranks hard (5-8 sec) , starts, idles slow and rough and stalls. Third try seems to work and idle is smoother and sustainable at normal 700-800 rpm. Alternately, on cold start if i hold the gas the car will continue to run and then idle smoother and sustain.
-I initially thot the problem was coolant temp sensor related but the sensor tests good with normal resistance values.
-I now believe what is happening is something in the fuel delivery and a fuel starvation issue.
-Does my logic make sense and would fuel pressure measurements to det if pressure damper and/or accumulator is bad make sense.
-Is another way to validate this to turn key on (dont engage starter but turn on the fuel pumps) and then engage starter to see if startup is smoother???Or do I have to jumper connections in the fuel pump relay ciruit to turn on the pumps??

I have replaced the following parts -- fuel pump relay, OVP,dist cap and rotor, plugs,cold start injector (valve).--and none to these components changes the startup problem.

In the course of diagnosing the coolant temp sensor i did observe that if i disconnect the coolant temp sensor from the CIS control unit the engine starts right up , but then stalls with rough idle. My guess is the EZL is sensing high res - full enrichment and then chokes the engine.

Any help appreciated.
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