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  #16  
Old 10-25-2002, 09:55 PM
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You might also want to check for vac leaks in the engine compartment -- I had to replace all the rubber connectors on my 300TE to cure the tranny shifting problem. Worst was the idle control valve hose -- rock hard and loose. Don't know if you have that, but if the vac supply line is loose, it can do strange things with the servos.

Don't know why that would cause your trouble, though -- should have higher vac at idle than at 1500 rpm.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #17  
Old 10-25-2002, 10:20 PM
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I was thinking of vacuum too. It doesn't make sense that it screws up at idle but is OK at higher RPM's, as you mention. Plus the temp thing is a little baffling, as that's electrically controlled.

Gilly
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  #18  
Old 10-25-2002, 10:33 PM
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Gilly:

Unless there is excessive engine movement and a vac line is opening and closing. Ditto for a corroded fuse making intermittant contact?

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #19  
Old 10-26-2002, 11:29 PM
Jackd
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Update:
I checked the mono valve operation: Looks OK, default to full heat.
Secondary water valve also OK. 1.1 amp. while running, no problem there.
Vaccum: At idle vaccum is at 14.9 BUT falls to 5-6 for a second or two, then back to 14+. This cycles 2 or 3 times than reverts back to full vaccum. That might be the cause.
What can cause vacuum to fall for such a short period and come back to normal? I checked all vacuum hoses, including those behind the glove box, everything seems normal. Engine idle is very stable (700RPM) and smooth even when vaccum drops.
Also, could a low alternator output at idle cause this problem?
thanks
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  #20  
Old 10-27-2002, 12:34 AM
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Jack:
I believe (not 100% sure) that the default for low/no vacuum is to direct the air flow to the windshield, so i don't believe the vacuum is affecting your problem.
Can you run the same tests as before, but with the water valve disconnected?
If you have a voltmeter you can put that on the battery and monitor the voltage while doing the tests, then trying to determine if the voltage drops off alot during the tests. With the engine running, nominal voltage will be 13.8 to 14.2 volts.

Gilly
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  #21  
Old 10-27-2002, 10:54 AM
Jackd
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I ran the test with the auxiliary pump disconnected. That does not seem to change anything.
Voltage at the battery varries from 13.0 and 13.2 volts at idle and climbs to 14.4 at fast idle (1500RPM). Tha battery is less than 6 months old.
jackD
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  #22  
Old 10-27-2002, 12:45 PM
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OVP relay dropping out?

I don't understand the intermittant vac drop with no idle speed change, either, this is odd. A vac leak big enough to drop the idle speed would make the engine go lean and at least shake.

Could there be an ignition fault here, so the idle control valve drops all the way open intermittantly? Hard to imagine that unless it also caused idle instability, too!

Could a bad O2 sensor do this by messing with the mixture?

Strange. Sounds like a huge pain in the sitting part, too!

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #23  
Old 10-29-2002, 07:13 PM
Jackd
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Update: I re-ran all tests over the week end;
Mono Valve: operates OK as it defaults to full heat when disconnected.
Auxiliary water pump: Operational as it should. Vacuum: I could not replicate the vacuum lost I saw the other day. I must have screwed-up on the first test. Vacuum is normal, engine idle very smooth at 700RPM. Disconnection a major vacuum line make it idle very low and shaky, which is normal.
I spent all day today at my Mercedes Stealership trying to diagnose the problem. 7 hours later at $88.00/hours+shop supply+1qt of coolant++++++=$775.00 to tell me they have checked everything and they could not find the problem. But they acknoledged the problem is real.
Still the same problem: Heater works OK until the car idles for about 1 minute it then switches to cold A/C. While on a/C, idle one minute and it turns the heater on. A tap on the gas pedal reverts the system to where it should be.They tell me they checked the heater controls, tried a new one on, still the same problem. What's next.???
JackD
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  #24  
Old 10-29-2002, 08:33 PM
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I could be wrong, but isn't the mono-valve on a 124 a needle and seat type as opposed to the familiar diaphragm?
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  #25  
Old 10-30-2002, 09:45 PM
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Jack:
Still sticking with my previous best-guess. The push button panel would cost alot less than $775, and if I was wrong at least you'd have a spare push button panel, or you could E-bay it. Surprised the dealer didn't at least off this as a possible solution.

Gilly
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  #26  
Old 10-30-2002, 09:50 PM
Jackd
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Thanks Dan. As I said in my post, the dealer tried a NEW climate control panel, and the problem was still there. They were good enough to put the old one back in when they saw it did not solve the problem. I don,t know what to do or where to look next, and they have no idea either.
jackD
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  #27  
Old 10-31-2002, 05:28 PM
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Sorry Jack, I missed the statement you made about them trying a push button panel. I guess I don't have a silver bullet for you on this one. Only thought I have is that I think I'd raise a little heck with the service manager about how $775 dollars is an awful lot to spend on an unsuccessful diagnosis job. I'd be a little steep even for a SUCCESSFUL diagnosis job.

Gilly
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