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Old 09-23-2008, 12:29 AM   #1 (permalink)
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Date registered: Jun 2005
Vehicle: GL 450 2008, E320 CDI 2005, E320 1994, 190E 2.6 5-speed(sold), 1995 E320(sold)
Location: San Diego, CA
Posts: 151
Strange idle surge problem

Hello All,
I need some help to pin point my car’s strange idle surge problem. I did a search in the forum and found lot of useful info but still not able to solve my problem.

Thanks to GDC and others for all the useful info.

Car: 1995 E320 with 129K

Cold start: starts fine, engine RPM around 1000-1100 and gradually come down to 700 RPM when gets warm (my other car 1994 E320 warm RPM is around 500, I don’t know why this car warm rpm is 700. Is it abnormal?)

Problem starts when the engine is warm, I mean when I start the car with engine temp between 40 to 80 (the instrument panel temp gauge). The car RPM will go from 700 to 1100/1200 then comes down to 400-500 for a second or two, engine shakes for 1-2 seconds and RPM goes back to 700 and no problem after that All these happen with 2-3 seconds. If I stop the engine and restart right away or even after couple of minutes, it starts fine. Rest of day, all day driving, at stop light no issues at all. The problem will recur if I wait for more than 15 to 20 min after stopping the engine.

The stalling is related to warm engine temp after waiting for more than 15 mins. I have replaced coolant/engine temp sensor, no cure. Replaced engine wiring harness, voltage regulator, changed MAF sensor from my other car which is working fine on that car, no cure. Checked the battery voltage at normal rpm and at 2000 rpm, no surge in voltage.

Other problems:
1. The air pump never comes on with cold start. I purchased rebuilt air pump, no luck. Replaced with another rebuilt one, no luck. I can not figure out why the magnetic clutch of air pump will not get engage, connections are ok.

2. Cruise control stopped working. Tomorrow I shall open Throttle Actuator and look for wiring degradation. I have already bought a used TA and cleaned it today. I need to buy the torx bit to open that.

3. The check engine light came on twice during last several months with code 4 and 8. While checking the code I noticed a small noise, something like a telephone dial tone type sound coming from the throttle actuator area, I can not pin point the source. After deleting the code it goes away.

I can not make any logical explanation for these strange behaviors. Any help will be appreciated.

Thank you all.
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Old 09-23-2008, 03:29 AM   #2 (permalink)
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Vehicle: 1993 400E 23100 miles "Gunter", 1999 ML320 200000 miles "Fizgig"
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suggest engine wiring harness and throttle actuator. Pretty classic problem these days. Describes all your problems to a Tee.
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Old 09-23-2008, 03:37 PM   #3 (permalink)
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Vehicle: 1993 300CE Cabriolet
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Cool Check your gas vapor recirculation valve

Hello, Ejaahm.

I had what sounds like the same problem you have with the idle surging up and down. It made driving the car in stop and go traffic difficult. I had to use neutral.

My indie M-B mechanic found that the gas recirculation valve at the charcoal canister was stuck. The new one cost over $130, plus labor. Now, the car idles just fine.

Best Regards,

Dave
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Old 09-23-2008, 05:40 PM   #4 (permalink)
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Quote:
Originally Posted by macdrone View Post
suggest engine wiring harness and throttle actuator. Pretty classic problem these days. Describes all your problems to a Tee.
Engine wiring harness was replaced 2 months back with a new one. No cure.

Update: Today I replaced throttle actuator (TA) with a old one from junke, the insulation of this junke unit was worst than my one and problem the problem increased, the car shaking all the time.
Looks like I need a new TA. Since I have a junke spare one, I shall take a chance to rebuilt as an experiment.

Dave,
Thanks for your response. Since my cruise control does not work with this problem it points towards TA. Does your cruise control works?

Thanks.
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Old 09-23-2008, 09:41 PM   #5 (permalink)
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Cool Could be lots of things

Ejaahm,

My cruise control worked even when I had the idle surging problem. BTW, the part that was replaced was called a gas vapor regeneration valve, not a recirculation valve.

I thought the problem was electrical, so I changed the plugs, checked the wiring, etc., to no effect. I didn't look at the throttle body and now I don't have to. That could be your only problem.

One of my shade tree mechanic friends also suggested checking vaccum lines and other pollution control valves.

I hope you find the problem. Post whatever it was on this thread.

Regards,

Dave
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Old 09-24-2008, 07:57 PM   #6 (permalink)
GDC
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You might also check your mass airflow sensor. You should be able to swap out with the one on your 94 as they both should be HFM sensors. Sometimes they get crudded up and cause surging as well. If swapping them quiets your car down you might try cleaning the sensor with either a cleaner made specially for airflow sensors or you might try carb cleaner.

Good luck
Greg
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Old 09-24-2008, 09:56 PM   #7 (permalink)
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Date registered: Jun 2005
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Location: San Diego, CA
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Quote:
Originally Posted by GDC View Post
You might also check your mass airflow sensor. You should be able to swap out with the one on your 94 as they both should be HFM sensors. Sometimes they get crudded up and cause surging as well. If swapping them quiets your car down you might try cleaning the sensor with either a cleaner made specially for airflow sensors or you might try carb cleaner.

Good luck
Greg
I tried cleaning the MAS with electrical connector cleaner and also tried swapping technique, no change.
When I open the MAS connection while idling the RPM goes up and down, reconnecting it corrects idling. So I am guessing MAS is alright.
My concern is why the idle surge is only during starting when engine temp is between 40 to 80 and after stopping the engine for about 20-30 mins. Rest of the time it revs smooth.

Greg: I called dealers today, prices are $2200 and $1470 at the two dealers I called. Now I am in the process of rebuilding my throttle actuator. How did you cut open the hard-shell connector at the end? I have already cut open one side, it's not opening. I am ordering Teflon coated high temp #26 wire Teflon Wire Sales, Electrical Wire #1, #16 Teflon, THHN Wire #12, Solid Copper #8 (the company says it good for 150+ C). Any recommendations?

Last edited by ejaahm; 09-24-2008 at 10:05 PM.
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Old 09-25-2008, 11:50 AM   #8 (permalink)
GDC
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ejaahm

Cutting that thing open was a bear. I cut as far as I could with a utility knife and made the final cut with a razor saw.

If you decide you need to replace it, I would recommend a rebuilt unit from Jaytan. I had to replace mine when the pot failed a couple of months after my rewire. I ordered a rebuilt one from Terry at Jaytan. The unit was packaged very well, but UPS still managed to destroy the box and damage the TA. I called Terry and he shipped a replacement same day with no additional charges and no wait until the broken one was sent back. Excellent service and a fair price around $700.00.

As far as the wire goes, anything with teflon or a crosslinked insulation should be fine. Make sure it is multistrand conductor though as a solid conductor will make fitting it in under the intake difficult.

Good luck
Greg

Last edited by GDC; 09-25-2008 at 03:08 PM. Reason: additional info
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