Mercedes-Benz Forum - View Single Post - Ever recurring DTC P0100
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post #7 of (permalink) Old 08-02-2013, 01:47 PM Thread Starter
Pop45398
BenzWorld Member
 
Date registered: Feb 2013
Vehicle: 1999 ML430
Location: East Texas
Posts: 395
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Quoted: 1 Post(s)
(Thread Starter)
Solved

Problem solved! It turned out to be the EGR valve not completely closing.

Recap for those with DTC P0100:

Symptoms:
*Intermittent recurring DTC P0100
*Intermittent erratic idle speed
*Intermittent very low speed surging
*Intermittent abnormal MAF rate at idle
*CEL always illuminated during idle or very low speed

Efforts prior to EGR discovery:
*Replaced cheap knock-off MAF sensor with OEM Bosch
*Replaced air filter
*Replaced air inlet duct to engine seal
*Insured inlet duct and crankcase ventilation hose properly seated
*Checked for external vacuum leaks with WD-40
*Checked wiring and connections between sensor and PCM

Deductions:
*Possible bad PCM
*Possible internal vacuum leak (possibly power brake booster or EGR valve)
*Power brakes always worked fine, problem intermittent
*Previously stuck closed EGR valve cleaned and freed, eliminating DTC P0400
*No DTC P0400, EGR valve open or opening

Inspection:
*Removed EGR valve
*Blew into outlet side (threaded fitting), air flowed freely with valve shut indicating major leak

Repair:
*Scraped carbon buildup as best as possible from inlet and outlet sides
*Filled inlet side with PB Blaster and allowed to soak awhile
*Repeatedly pressed down on diaphragm with end of plastic brush handle and released to work valve open/closed
*Jammed brush handle between diaphragm and frame to hold valve open
*Bent thin wire in two and fished looped end through outlet side to inlet side
*Inserted gun cleaning patch (or small piece of cloth) soaked with cleaning solvent through loop in wire
*Pulled wire with patch/cloth back through valve opening
*Removed brush handle allowing valve to close
*Blew into outlet side to check if valve fully seated and no air flow through valve
*repeated as necessary till air flow stopped (would purchase new EGR valve if unsuccessful)
*re-installed EGR valve
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