Engine Idle Fixed

The idle speed was getting steadily worse as time passed. A few weeks ago I put the Merc away for a while because the high idle was becoming intolerable. I would be idling at 1600 rpms while hot and in neutral. Also, while underway, the car would speed up to about 60kph with my foot off the throttle.

I was able to switch IAC valves with the buddy with another 560 SEC. This brought the idle speed down a couple hundred rpms. We knew his was probably bad as well, but it was certainly in better condition than mine. His car is the ECE version, with a different fuel injection system, so minute differences in how the engine controls idle probably resulted in a measurable difference in idle speeds despite having the same basic engine and same IAC valve. Mine idled a bit higher than his with the same valve.

Anyway, it was clear that despite getting a clean bill of health from my mechanic last winter, my IAC valve was in dire need of replacement.

It's a relatively expensive part. I didn't even dare ask how much it costs at Finnish retailers. I know from reading forums that it's in the hundreds. So, we organized a group order from Autohaus AZ with a couple 560 SEC owners. They stocked both the VDO (original) valve and related rubber hoses at a fair price ($185 for the valve and about $10 for the hoses). Autohaus AZ has a great stock of OEM M-B parts even for rare models, and very reasonable prices.

After about a 3 week pause, I'm driving the Merc again. I have to say I was beginning to miss it pretty bad. For the past weeks I've been driving my dad's 1969 Renault.

First impressions with the old friend 560: damn it's big, damn it's comfortable, damn it's quiet, damn it feels heavy, damn it has a great soundtrack.

Here's where the IAC valve goes. Removing it is really easy, literally a 5 minute job. You only have to take off the air filter casing. After that, and removing the electric connector, the IAC valve lifts off the metal and plastic pipes you're seeing here. Originally there's a rubber fastener around the valve, as seen in the next picture, but mine was broken and didn't really do anything, so I just left it off. Better take the right side rubber hose off first, while dodging the vacuum connectors on the left. They are fragile and cause problems if they break. After this the IAC valve wiggles off the downward facing pipe.

Here's my old IAC valve. You can feed it 12 volts, polarity does not matter. If I understand correctly the valve should close completely with 12 volts. In the picture it's powered up but has only closed the amount you can see there. I think this was responsible for the high idle speed.

Here's the new valve installed. As you can see it's really polished and looks like a quality part, as it should, since it's a VDO (original part). The new rubber hoses were pretty soft and had a really snug fit, totally unlike the old hoses. I was probably sucking in lots of extra air through the rubber hose fitting imperfections with the old parts. That probably contributed to the high idle issue.

All said and done! Once I fired it up it immediately felt more healthy.

It did the usual rpm adjustment routine like it should, ran 10 seconds or so at 1000+ rpm, then brought the idle speed down a notch, and again after a while. I'm now idling at about 500-600 rpm while warm and in gear, and about 800-900 rpm while in neutral. No irregularities or anomalies in the idle speed now.

This fixes a lot of issues. Now since the idle is so low (normal), engaging a gear doesn't feel as violent as it did before. Also, the car sounds much healthier since it's not constantly "fighting" the high rpms. I'm also now probably using a bit less fuel. Win-win.

First Year Sit Rep

The 560 has now been in my possession for exactly 1 year. During that time, it covered 8300 km. I've bought a total of 1290 litres of 98 octane. That makes average consumption 15,54 l/100km. This is almost exactly in line with what I get on a per-tank basis these days. "Cheap 98 octane" was 1,39 EUR / litre when I bought the thing, now it's 1,59 EUR/l.

As for total cost of ownership over the year... Let's just say it's over 50 % of the purchase price. But then, a lot of it has been spent on custom work and restoration; not just maintenance and repairs.

Little Things

The man who sent me the mint kickplate for the previous posting also sent me a nice original gearlever:

It's made of really sturdy leather, and is in mint condition.

It's a real bitch to install, though, so it'll have to wait a bit. In order to install it, I'd have to crawl under the car, and also take most of the car surrounding the gearlever apart, which includes the lower part of the center console. This is not something that can be done in late September...



In other news, I managed to change the bulb in the headlight switch.

Technically this is two bulbs. One is for the foglight caution light, and one for the surround lights. The latter is derived via fibre from a single bulb.

Pull off switch, pull off foglight bulb, undo the large flat nut, pry off switchplate, pull out the rectangular bulb housing from the back. Repeat steps backwards, done. Based on memory I think this goes for at least the W126, W124 and W201 Mercs.

It's noteworthy that the OEM bulbs in Mercedes consoles are both low wattage and slightly fogged. These you have to source from a dealership or an OEM part supplier. You can get correct wattage bulbs from spare part retailers but the shade will be slightly off, due to the bulb lacking the fogging. The bulbs are about EUR 2,50 per. Like I said the headlight switch assembly takes 2 bulbs. On manual A/C, the air controls take 4. Gearshift illumination consists of 1 bulb. Note that this is for my car only. If I recall correctly, old W126 models have some differences.

Engine Idle Relay & Exploring the Passenger Footwell

Last week I went to visit a friend who also has a 560 SEC, and borrowed his engine idle relay. The high idle speed problem was not fixed, but the effort wasn't a complete waste: it appears my idle relay is functioning correctly, or both of ours are broken. Anyway, next in the saga of high idle speed I will again be looking at the Idle Air Control Valve.

The idle relay is housed in the passenger footwell, next to other electronic equipment such as the OEM alarm system, Webasto control unit and stereo cabling. This space is covered by a plastic "kickplate" that is tightly fastened to the firewall with a plastic nut. The floormats rest atop the kickplate. While we were swapping idle relays, I found that my kickplate had gone missing at some point in the cars life. I turned to my trusted W126 spare parts guru and he sent me a mint part along with the special plastic nut. Here's some pictures of what a W126 footwell looks like. Note that mine has a lot of non-OEM cabling for the retrofit alarm and stereo.

On another topic: We looked at the W126 microfilms and it appears the OEM radio for this car was indeed the Becker Mexico Cassette Diversity. The Diversity was a revised model of the Mexico Cassette unit, and was introduced in I think 88 or 89. It was the first radio with a dual tuner and featured, for example, automatic volume adjustment for vehicle speed. The radio reads a signal coming from the speedo. These radios are pretty rare to find as standalone units, usually they have to be sourced from a "spares" car. Refurbished units in retail can go for as much as 500 EUR. On eBay, they cost anywhere from 150 to 300 EUR depending on condition and accessories. I may have a chance of sourcing one with a minor technical issue from a forum buddy for about 140 EUR but this remains to be seen.

Exhaust v2.0

Today I got the car back from another shop. They re-did the exhaust tips for me. They weren't very nice about the quality of the previous tips which is understandable. There were some things about them I didn't like either. While they were at it, I had them take the catalytic converter off. I asked them to make an H pipe in its place and mount the lambda sensor in the crosspipe, but they said that was not optimal, it would have to be more of an X pipe for that purpose. That, on the other hand, would've been pretty expensive, so they ended up using the tip of the old cat. They said this results in a great flowing part that fits well with the surrounding pipes. I trust their judgement so that is how the exhaust was done.

General cat area as it stands now:

Complete exhaust:

I have to say, I'm especially happy with how the new tips turned out.

Removing the cat had a tremendous effect on exhaust sound. I had no idea the Mercedes catalytic converter muffled the sound this much. The exhaust is now pretty loud outside the car, and drones inside ever so slightly at 80kph. I would not dream about removing any more mufflers, it's perfect the way it is.

Here's a video of the new exhaust in action. No inside footage, sorry about that.

Mindless Trivia

I was bored to tears at home so I did some digging for some nuggets of trivia.

Did you know?

• When this car was new, in Finland it cost 1,1 million marks, or about 280 000 EUR, adjusted for inflation. In America the US model cost $145 000.
• There were a total of about 28 900 560 SECs produced, of which about 17 700 were facelift models, of which about 5000 were 1989 model year, and about 3000 were Euro models like mine. My car, therefore, is one out of about 3000 like it.
• There are about 285 560 SECs on the road in the UK, right now. That is across all model years and versions. Since the 90s, where the data starts, about 4% of 560 SECs have disappeared from the roads per year. Using that number as a basis for extrapolation, my car is currently 1 of about 9550 facelift 560 SECs left (1989-1991, US+EURO models).

Differential Woes

Ever since I first test drove the car, I knew the differential was going to be a serious achilles' heel. 5000km ago, on the test drive, it howled at 80kph like any Merc diff that had seen a lot of highway miles. Since I've been driving it, the howling hasn't gotten much worse, only it now happens on 85kph too. New to the situation, however, is a ticking (sometimes a crackle) coming from somewhere near the backseat. I started thinking oh-my-god, the diff is going to let go real soon.

I'd been waiting for fall in order to clean up the wheel lug thread grooves in the front. I figured since there is probably going to be a diff overhaul, and the car will be sitting for a while again, I'm going to do it now, and switch to Pentas/winters while I'm at it. This was last week.

Today I had an appointment at the shop. We opened the diff to start diagnosing the ticking. Well, first off, the diff wasn't dry. I'm not sure how much oil there was exactly but one thing was for sure, it looked pretty awful and it wasn't certain if it was the right kind. The diffs on 560's are pretty cranky about having just the right lubricant. After all, they are viscous LSD's, and Merc ones at that. I read a recommendation for Mobil HD 80W-90 hypoid oil but asked a buddy what he'd bought. He recommended LiquiMoly LS SAE 85W-90 oil which is for Limited Slip Diffs obviously. So that's what I got!

Old Diff Oil

New Diff Oil; LiquiMoly LS SAE 85W-90

I didn't take a very long test drive (road temp was 38C and I was running frictions) but the result is this. The diff feels like it howls a little less, but the ticking is still there.

While I was at the shop, an old taxi driver threw an interesting idea: what if it's a wheel bearing. Well, it certainly could be, and I started leaning in that direction initially, until I remembered something; the car only makes that ticking noise when cruising at 85 kph. If you let off the cas, it stops, and if you accelerate, it stops, even at the precise speed where the noise happens on steady gas. So I'm still thinking it's a bearing in the diff. Oh, and there was no evidence of metal in the old oil, or in the drain plug magnet. It's therefore pretty unlikely that anything else besides a bearing is damaged inside the diff.



Other than the diff problem, 560SEC ownership has been pretty mundane recently. I went to Lappeenranta Cruising a couple weeks back, for which I washed the thing and took the ten minutes to maintain the engine bay's cleanliness. Here's a pic I took while I was cleaning the lug threads.