94 C220 Very High Idle In Park or Neutral - Mercedes-Benz Forum

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Old 10-09-2013, 07:18 PM   #1 (permalink)
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Date registered: Oct 2013
Vehicle: 1994 C220
Location: Renton, WA
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94 C220 Very High Idle In Park or Neutral

Just picked up this C220 for free and made a 900 mile trip from San Francisco to Seattle. About halfway there the car started to overheat then I lost power. I determined it was a faulty serpentine belt so thankfully I finally lost all power infront of a Napa Auto replaced the belt and everything was fine for the rest of the trip.

Now after that little backstory the issue I'm having is the car will idle around 2000rpm in park or neutral. I've checked every vacuum line, cleaned the throttle body and MAF, and lubed the throttle linkage as suggested by the searching I've done but seemingly no change.

Before I go and try a new (used) throttle body, any other possibilities that would be causing this?
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Old 10-10-2013, 07:30 AM   #2 (permalink)
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What makes you think it's the throttle body?
Do you have a cel?
Have you tried disconnecting the mad while the car is running to see if there's any difference?
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Old 10-10-2013, 07:33 AM   #3 (permalink)
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Vacuum lines... check all those out, may also want to check through the wiring harness for any issues as well, but something there would probably be more obvious (CEL).
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Old 10-10-2013, 08:16 AM   #4 (permalink)
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Date registered: Oct 2013
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Quote:
Originally Posted by mikhail.abraham View Post
What makes you think it's the throttle body?
Do you have a cel?
Have you tried disconnecting the mad while the car is running to see if there's any difference?
I thought it may be the throttle body as I've seen several posts about unusual high idle issues and throttle bodies. No CEL. I have disconnected the MAF with no change to the idle in park.

Quote:
Originally Posted by mgill85258 View Post
Vacuum lines... check all those out, may also want to check through the wiring harness for any issues as well, but something there would probably be more obvious (CEL).
I'll have to recheck the vacuum lines. The wiring harness for the most part looks alright. I've cut some of the insulation open to inspect them.
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Old 10-10-2013, 02:51 PM   #5 (permalink)
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Date registered: Dec 2011
Vehicle: 1996 C220 Auto-tragic
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Check to make sure the spring on the bell crank of the throttle body is not broken. This holds the throttle butterfly closed against the 'closed' switch inside the throttle body. This tells the ECU to control the idle with the idle control motor.

I can take picture later but is on the front of the manifold by throttle body easy to find and replace. The spring is near where the linkage connects to the throttle body.

Also could be engine wiring harness if hasn't been replaced.
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Old 10-10-2013, 06:34 PM   #6 (permalink)
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Date registered: Oct 2013
Vehicle: 1994 C220
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Quote:
Originally Posted by kmax7 View Post
Check to make sure the spring on the bell crank of the throttle body is not broken. This holds the throttle butterfly closed against the 'closed' switch inside the throttle body. This tells the ECU to control the idle with the idle control motor.

I can take picture later but is on the front of the manifold by throttle body easy to find and replace. The spring is near where the linkage connects to the throttle body.

Also could be engine wiring harness if hasn't been replaced.
Spring looks good and intact.

Quick update: I pinched off the vacuum line to the transmission (clear) according to the diagram and it reduced the park idle to 1300. Now it appears this would be multiple vacuum leaks then, possibly a bad EGR? As far as the transmission goes, maybe a broken vacuum line or a faulty modulator?
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Old 10-13-2013, 07:52 AM   #7 (permalink)
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Anymore ideas before I jack up the car tomorrow? Going to look at the vacuum modulator and lines on the transmission.
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