Hey guys,


So as of a week now, the 560SEL has been doing a really weird thing when I start it up when 'warm'.

It'll start right up, and then after maybe 4 seconds, the economy gauge reaches the mid point, the rpm's drop below 500, and the oil pressure drops to 2.

It sort of rumbles, so I'm guessing this isn't something I should just let happen, but what could be causing such a thing? After letting the car do its thing, it generally goes away after 20 seconds, revving itself up to about 1100, and then back down to 950.


Thanks,


Carlen

Forgot to mention that also on occasion when warm, I'll turn the key, it'll start, and the rpm will climb to 1200, and when on it's descent back to where it would idle, it just continues downward and dies.

I then can restart it, and it'll do that whole weird thing it decides to do.

After driving her the past two days, the thermostat gauge is acting realllly strange ALL the time; It'll start reading at the bottom, and then work its way up to the 80 degree mark, but usually at that point, it'll JUMP to over 120 degrees, and while highway driving, it'll move anywhere between 80 and 120, and I have to hit the dash to make it unstick from the 120 degree mark.

I guess I need a new Thermostat? Probably a coolant flush while I'm at it.

Could just be a bad ground on the gauges too.

If you can get it running, and stay running... check your idle vacuum.

Also verify your engine/body grounds and the battery ground. That can cause issues too.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Oh the idle vacuum is as low as possible; she runs after one or two start-up attempts.

I have the work manual, but where do I check for these grounds?

My battery ground is pretty chewed up; I'll take a picture sometime tomorrow.

Thanks,


Carlen

Well a bad battery ground is never good, one of my BMWs would not even start with semi loose battery connections. I am not sure how sensitive these cars are to charging systems, but verify the alt connections and its output.

I know one of the body grounds is from the steering pump bracket to the fender area.

Well consider this also: the newest M116/7 here in the US was built in 1991. That was 19 years ago, maybe 20 depending on build date. The early ones should have come out late 1985 which is 25 years ago! So most of the rubber under there is in dire need of replacement.

Pull the air cleaner assy off and nose around. Just touch and squeeze all the stuff to see if it is pliable, if not... well that would be a good place to start before attempting to further fix issues. Do not forget, the intake manifold is a two piece... so the eight o-ring looking seals need to be replaced also. This is a real PITA. Also the fuel distributor boot to throttle body shrinks with age.

Four and three way connectors go bad too. Any oil leaks are vac leaks...

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Just a WAG but in addition to Hit Man X's good suggestions, what about the idle air control solenoid right in front of the air cleaner box?

The 560SEL/SEC vehicles are well known for a high idle problem that can occur at higher miles on the car

The mechanic notes said in part:

"A check with an ohmmeter showed an intermittent connection to the solenoid ~~~ 5 ohms or infinity, depending on where I banged the unit with a rubber hammer, (after removal from the intake manifold). Since it was bad already, a dremel was used to grind off the lip that had been bent in to hold the connector in place.

After gently pulling out the connector, a broken lead was revealed from one of the connector pins! A few minutes with a soldering iron and some cafeful application of 5-minute JB weld and Jim's car idles at 600-700 RPM. Don't throw away those old $250 solenoid air valves, they might be repairable."


( This was done at 90,500 miles/13 Aug 2001, --- just before the 9/11 attack ) ... the car runs perfect ever since, this trouble never recurred, and the vehicle is now at 168,000 and over 8 years later....)

__________________
1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)

I've actually changed out most of the rubber in this big ol' block; my last vacuum issue was actually pretty embarassing, as it was the vacuum line to my brake booster that wasn't just leaking, but severed Took 3 guys and a mechanic to find that one...

And as for the IAC, I've taken that thing out and cleaned it with what seemed like no significant improvement; whenever I do disconnect it though, it jumps to maybe around 2000 rpm, which makes me inclined to believe it might be the ICU instead of the valve...

I drove it today, and it did the erratic thermostat deal again, but it didn't do the strange idle issue any longer than 4 seconds.

This thing is driving me crazy

Thanks guys,


Carlen