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  #1  
Old 12-15-2007, 11:37 AM
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C 230 Rpm Idle Fluctuation

WELL after throtle body clean its still there.

AT IDLE RPM'S GO DOWN THEN BACK UP WHILE IN DRIVE AT STOP LIGHT AND IDLING, NOT EVERY TIME. OTHER THEN THAT NO PROBLEM WITH ACCELERATION AND CEL NOT ON. AFTER ENGINE IS REALLY WARM IT WON'T DO THIS. INDY MECHANIC SAID DIDN'T DO IT TO HIM SO DOES NOT WANT TO JUST START REPLACING PARTS.

WHAT WOULD CAUSE RPMS TO FLUCUTATE AT IDLE?

SPARK PLUGS CHANGED 6 MONTHS AGO AND NOTICED IT AFTER ONE MONTH. CAN THAT DO IT.

1998 C 230.

HELP, TIRED OF PAYING THESE GUYS THAT HAVE NO IDEA, OR NO EXPERIENCE.

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  #2  
Old 12-15-2007, 12:30 PM
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Did you install the correct sparkplugs?
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  #3  
Old 12-15-2007, 01:37 PM
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Air pump self test. Normal. Didn't we have this conversation already? Turn your caps lock off, it's annoying.

If the car experiences a 1-2 second dip in the idle, with a "shudder," then runs fine the rest of the time and no CEL, then what you're experiencing is the air pump self test. I've owned my C230 since new, for 240,000km now, and it has done it since new, and always will as long as the air pump is working properly.

You can keep throwing time, money and effort at solving this problem, but I doubt you will ever be satisfied. The car has a normal system operation that causes a slight idle drop. Get used to it.

Don't clean the Air Mass Meter. You're asking for trouble. They were not meant to be serviced, and even if it was failing, at best you bought a little time. The failure of the AMM causes a fuel trim adapation problem and is easy to diagnose. First, 95% of the time it will throw a CEL then you'll have a terrible hesitation at 4500rpm and above. Driveability will be effected.

Now that you screwed with the AMM, I'll bet that sometime in the not-too-distant future it will go out on you. If you get code P0170/P0171, then have the adaptations read and I'll bet they be maxed at 1.32 and you'll need a new AMM. BUT, the symptoms are different than what you're describing.
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Last edited by blackmercedes; 12-15-2007 at 01:46 PM.
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  #4  
Old 12-15-2007, 01:47 PM
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Quote:
Originally Posted by LORE BENZ View Post
WHAT WOULD CAUSE RPMS TO FLUCUTATE AT IDLE?
See my post above.
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  #5  
Old 12-15-2007, 02:40 PM
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Quote:
Originally Posted by blackmercedes View Post
Air pump self test. Normal. Didn't we have this conversation already?
YES
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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra
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  #6  
Old 12-16-2007, 12:21 PM
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I cleaned T.B. and not M.A.S.

COULD incorrect plugs or not tight enough cause this same symptoms?


Sorry for capital letters, just tired of mechanics who are supposed to know about abnormal and normal variants.


I AM asking because for 100,000 miles this vehicle has not done this self pump air test SO not a normal variant and very noticeable! Only real change are spark plugs.

COULD IT BE PLUGS, NOT RIGHT SIZE,OR TIGHT, LOOSE?

Last edited by LORE BENZ; 12-16-2007 at 12:27 PM.
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  #7  
Old 12-16-2007, 12:42 PM
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Quote:
Originally Posted by LORE BENZ View Post
COULD IT BE PLUGS, NOT RIGHT SIZE,OR TIGHT, LOOSE?
What plugs did you install?
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  #8  
Old 12-16-2007, 12:45 PM
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I Didn't Do It, Mechanic Stated He Went
To Dealer For Oem Plugs.

Can Plugs Cause These Symptoms?
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  #9  
Old 12-16-2007, 01:05 PM
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Try this:
Turn the key to " ON ". ( DO NOT START the engine ).
Push the gaspedal ( slowly ) all the way to the floor.
Hold it there for 10 seconds.
Release the gaspedal.
Leave the key " ON " for 2 minutes.
Start the car & see what happens with your idle.
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  #10  
Old 12-16-2007, 01:06 PM
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What Am I Looking For?
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  #11  
Old 12-16-2007, 01:38 PM
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BEFORE I do steps i have to know what i am/am not looking for and to

diagnose what exactly?
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  #12  
Old 12-16-2007, 02:05 PM
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Quote:
Originally Posted by LORE BENZ View Post
Can Plugs Cause These Symptoms?
Read sticky post #1 at top of page.

On my 99 the procedure in your thread, post #9, will reset the trans adapation values.
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  #13  
Old 12-16-2007, 02:53 PM
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Man, this thread is all over the place! Spark plugs, Air Injection, Transmission adaptation, etc. The answer probably isn't too hard to find, as long as you look in the right place. I realize not everyone has SDS at their disposal, but here's what I'd do if I was working on the car.

It sounds as though the throttle actuator could be the problem. The first thing I'd do would be to make sure the fuel trim values are within specification. This is a reliable, fast way to eliminate the possibility of a lean/rich condition causing the problem. If that checks out good, I'd activate the throttle actuator using SDS. It's a simple test, done with the engine at operating temperature/idle speed. The throttle is slowly closed, lowering the idle in small steps. Then I'd see if I was able to open the throttle up again. Sometimes the actuator simply isn't strong enough to overcome the throttle return spring. I see lots of this on higher mileage M111's. The result is a fluctuating idle because the actuator doesn't react quickly enough to stabilize it.
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  #14  
Old 12-16-2007, 04:02 PM
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I am not sure I am clear on the EXACT symptom. Is it:

A) Fluctuating idle

B) Idle drops ONCE for 1 second or less and that is it, until the next time you drive the car from a cold start.

A or B?
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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra
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  #15  
Old 12-16-2007, 04:30 PM
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When car is started it does not do it, never does.

I can drive 20 miles at 60-80 m.p.h. without problem after that, then when at first long stop light, R.P.M. CAN go down slightly then back up to normal. NEXT light it may do it again and thats it for rest of drive.

IT will do it 2 miles from my house at stop light or stop sign, so not necessary for completely cold car, but after stop and go for a while it may do it again.

NEVER a loss of power at high speeds, no cel.

I CLEANED t.b. THEN CEL CAME ON AND OFF AGAIN without those jerks forward 2nd or 1st manual gear thereafter gone.

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