The 560SL Throttle Valve Switch Replacement Narrative

[BabyBlueBenz]

In pursuit of reducing the high idle speed my 1986 560SL had been experiencing, I determined that the Throttle Valve Switch (TVS) was bad. The test procedure is outlined in Service Manual document 07.3-152 "Checking, renewing throttle valve switch". The experience detailed below was guided by 07.3-230 "Removal, reinstallation of throttle assembly" and 07.3-225 "Removal, reinstallation of mixture control unit". Besides the new TVS, you will need a new Throttle Housing Gasket and perhaps a handful of new vacuum line rubber elbows. For additional cleanliness, buy a few cans of carburetor cleaner or your favorite degreaser. A shop vacuum would be practical as well.

For my preceding high-idle adventure, see the thread "Idle Speed Air/Control/Slide Valve Confidence Check" at http://www.peachparts.com/shopforum/showthread.php?t=243090.

In a nutshell, this job is not as bad as I thought it would be. In fact, I'll be doing it again soon, because of reasons mentioned below.

Break out the toolbox, 'cause here we go...

[BabyBlueBenz]

Here's what we're dealing with...the topside of the M117 engine with its CIS-E fuel injection system. This view is front-to-rear, with the distributor at the bottom of the photo and the firewall at the top. Pardon the filth and rust...I'll get to those tasks someday. The TVS is located in a hole as pointed to by the arrow. You can't reach it until the Mixture Control Unit (MCU) & Air Guide is removed.



Here's a close-up with the partially-visible yet dirt-encrusted TVS highlighted in red.

[BabyBlueBenz]

First, open the fuel filler cap to release the pressure on the fuel system.



Unplug the wiring plug to Idle Speed Air Valve "Y6". Loosen and remove the clamp securing Y6. Remove Y6 along with the two black rubber elbows connected to it by twisting it to the left to slip off the first elbow and then pull upward on the second elbow, which is held snug by a barbed plastic fitting atop the black Air Guide. Set these parts aside.

Unplug the Air Flow Sensor Position Indicator "B2".

Carefully disconnect the vacuum line at the back of the fuel Diaphragm Pressure Regulator "40". I pulled mine too hard and the rubber mushroom fitting came out of my regulator. A little soap and a small screwdriver convinced it to go back in.

Unplug the Electrohydraulic Actuator (EHA) "Y1" at the back of the MCU.

[BabyBlueBenz]

Find the large fuel line leading to the MCU. About midway in the exposed metal portion of the line is a welded-on bracket, which is fixed to the base of the MCU with a 10mm bolt. Remove this fastener and set it aside.

Get a hold of some paper towels or discardable rags to absorb the upcoming spillage of fuel.

With a 17mm wrench, slowly loosen the large nut retaining the Fuel In line at the MCU. Prepare for some minor squirting of fuel onto your rag/towel. Should the amount of gas overwhelm your catch rag/towel, simply tighten the fitting again and get some more rags. Once free of the MCU move the loose end of the fuel line aside and place a fresh rag/towel beneath it to catch any more gas that might leak out.

Using the same rag/towel catch scheme, loosen the fuel return line at regulator "40". Now my car has had its fuel cooler removed, so your fuel line arrangement will likely differ from my photo. Once freed, swing the loose ends of the fuel lines over the valve cover.

Remove the two flat-head screws holding the EHA onto the Mixture Control Unit and set these three parts aside. A little fuel may drip out of the EHA and MCU.

[BabyBlueBenz]

With a 12mm wrench, loosen the first of nine injector connections, starting with the Cold Start Valve "Y8". A small amount of fuel may drip from these lines. Make sure that the retaining nuts are completed unthreaded from the injectors.

Continue loosening the remaining fuel injector lines. They were fairly tight, so I applied a bit of a counter-hold on the rigid fuel lines themselves.

[BabyBlueBenz]

The Breather Hose from the driver's side valve cover is held in place by a small tab fastened by a 6mm Allen-headed bolt. Loosen (no need to remove) this bolt and the tab will swing aside. Pull this end of the breather hose up and off, then swing it toward the front of the car.

Hiding beneath the breather hose is the plug connection known as "S29/2x1"...unplug it. UPDATE: This junction is also known as "X56" in the service manual. The bottom/male portion of this connection is fixed with two 10mm bolts. Remove them and set the bolts aside. The male connector you just freed is the pigtail end of the TVS.

Nearby is the Coolant Temperature Sensor "B11/2" with its two largish barrel-shaped pin connectors. Unplug these two and route the wire so that it will not tangle with the fuel injector feed lines.

On the passenger side, disconnect the forward end of the long throttle rod linkage. The socket end will pull off with a mild tug. Swing the rod aside so that it doesn't lie atop the injector fuel feed lines. If your car is equipped with a Cruise Control Actuator, the aft link will need to be disconnected as well.

[BabyBlueBenz]

At the four corners of the base of the MCU are 10mm nuts with wiggle washers. Remove the nuts (the front passenger side is actually a standoff tower) and washers and set them aside. I spent several minutes fishing out those wiggle washers, because I knew that I'd want to clean the MCU & Air Guide and they'd get lost. UPDATE: The second time I extracted the MCU & AG, I left the washers in place and just took care to fish them out from the assembly once it got to the workbench.

With your can of WD-40 or PB Blaster, squirt a little juice onto the lock of the Air Guide clamp hiding in the hole near the TVS.

Take a break. Get something to wet your whistle or have a smoke. When you come back, use a long flat-bladed screwdriver or the appropriate socket on a long extension to your ratchet and loosen the large hose clamp that secures the Air Guide to the Throttle Body. Mine was pretty tight, and cracked open loudly (on hindsight a bad sign). Open the clamp enough to create a visible gap around the (partially invisible) perimeter of the clamp.

Check the tangle of unplugged wires and hoses that you've created and anticipate what might snag when you pull the MCU out with its nine long fuel-line legs. When you're ready, find some purchase on the MCU with your fingers and tug straight up. My MCU felt like it was still bolted on somewhere, but it finally came free with a reach from over the driver's side fender and pulling on the passenger side of the MCU. Once released from the throttle, lift the MCU & Air Guide assembly slowly and carefully up and out of your car and set it someplace safe. I propped mine up on two 2x4's so that the Air Guide would rest flat (didn't want the mouth getting distorted).

[BabyBlueBenz]

Here's the view of my car's innards after removing the MCU & Air Guide:



Despite the enlarged access, the TVS is still not removable because its mounting screws' heads are oriented to the right side of the throttle body. So the throttle must come out.

Get some masking tape to make labels identifying the four vacuum lines that are connected to the throttle body at various points. If you’re lucky, all these lines might still be connected. The diagram in service manual document 07.3-013 "Function Diagram CIS-E Injection System" would be handy to have in understanding where these lines go. Disconnect and label each vacuum line as you see fit.

With your needle-nose pliers, grasp the top loop of the spring leading down to the throttle and extend it a bit to clear its hook. Once relaxed, lower the spring a bit to clear its bottom hook and remove the spring and set it aside.

Disconnect the upper socket from the downlink rod. Let the rod rest where it is.

[BabyBlueBenz]

Barely visible in the photo, there are four small Allen-headed bolts securing the throttle. Try to clean out the bolt heads before inserting your best Allen wrench or socket and give them a turn. Carefully extract those four bolts and set them aside.

You're now ready to reach in and pull out your throttle...except it probably won't budge. Mine took a lot of "convincing" to come out, with the magic moment occurring with a prying using a large screwdriver between the backside of the throttle body and the intake manifold. Be careful, as there's a lot of breakable aluminum in the area.

Going back to the male connector base at S29/2x1, I cut its wire to avoid trying to unthread it. An alternative (whose reversal is how I threaded in the new TVS), is to raise the throttle body up far enough to turn it sideways and access the two TVS retaining-screws. Pull the TVS sensor off the throttle body and then unthread it through the meandering path to the junction.

Once unbound, the throttle will come up and out of the hole with just a little bit of twisting motion.

Should you be brave enough to peer into the depths of your Intake Plenum, prepare yourself for a ghastly site. Mine was coated with a caramel-looking crud. I would have liked to make this go away, but I saw no practical method for cleaning this mess without a full intake manifold removal. That day may come soon, since with the experience related above, I now feel confident to delve deeper into my V8 in the future.

[BabyBlueBenz]

I took the opportunity to clean my throttle body and the butterfly valve within with some carb cleaner, a soft brush and some elbow grease. You will also need to remove any remnants of the old Throttle Housing Gasket from both the Throttle Body and the Intake Plenum in the car. Here are some shots of the Before & After:



Note that I prematurely connected the TVS to the throttle before realizing the need to route the sensor end of the wire through the desired path from the S29/2x1 (a.k.a X56) junction.

I replaced the rubber vacuum line elbows in "the hole" before reinstalling the throttle atop its new gasket. AFTER getting the Allen-headed bolts tightened, I reattached the vacuum lines where they belonged (two of mine got capped...another story). Here's the happy throttle with its new TVS:



So now the cleanest spot on my car is where you can't see it!

The remaining reinstallation is just reversing the steps outlined above. I also cleaned my MCU & Air Guide with some carb cleaner, inspected the underside of the Air Guide for cracks (it didn't have any: see timm9's cracked example at http://www.peachparts.com/shopforum/showpost.php?p=1920679&postcount=15), and lubed those hard-to-reach throttle linkage joints with some ATF. Once all back together, the engine took a little longer to start as it reprimes the fuel lines. My resulting idle speed improved about 300 rpm toward sanity. My idle is still not the ideal 600-750, but I've got more tasks ahead to remedy that.

Another "while-you're-in-there" task worth performing before reinstalling the MCU is to replace/clean/repair your Fuel Injectors, their Insulators and Seals. I planned to do that, but one part arrived damaged...so maybe next time...which will be soon, since I broke the big hose clamp securing the Air Guide (it fits so snugly, I didn't worry about near-term leakage) . When I get a replacement clamp, eight good injector insulators & seals, plus a new (revised) Idle Air Distributor line I will pop my MCU off again. I may even take it further and remove the intake manifold to replace my eight rock-hard Manifold Seal Rings and clean that gunk out of the Plenum.

[450slcguy]

Very nice, I've pretty much done the same exact thing.

I wish I had also gone the extra mile and removed the top intake manifold and replaced the 8 donut shaped seals underneath it. Most of the work is done at that point of disassembly, just a few more bolts to remove and the intake manifold and it's off.

8 new donuts and new manifold gaskets cost maybe $50 total, not much money when considering the job would be complete and you wouldn't have to go back and address all over again. I still have my high Idle and believe if I had gone that extra step, all would have been better.

Oh well, live and learn. When the weather gets a bit warmer, I'll do it all over again and replaced what I missed the first time.

[Gurunutkins]

very nice write up and great pictures

[BabyBlueBenz]

I completed this threads "mission" today. The injectors and their insulators & seals came out pretty easy compared to what I had read about other forum members' experiences. No broken pieces of plastic.

The two vacuum distributor hoses that snake under the MCU & Air Guide were replaced. I was hoping to receive the updated design from my MPG as mentioned at the back of service manual 07.3-112, but the new hose did not feature the internal rib described there. It was slighty different in shape. I replaced the stock 42mm barbed plastic couplers with the revised spec 53mm couplers. While the rubber manifold tubes were off of the insulators, I cleaned and inspected it for cracks...none found, and the rubber was nice and pliable.

The wife and I both scanned the Air Guide for cracks and found no suggestion of such. The rubber was stiff but not hard, which is impressive since a molded date stamp said "86".

I was able to improvise a replacement for the unique Normetta clamp used to secure the Air Guide to the Throttle Body. For a pic and details, hit the thread http://www.peachparts.com/shopforum/showthread.php?t=246635.

[motozine]

I reattached the vacuum lines where they belonged (two of mine got capped...another story).

What's the story there?
So 4 vacuum lines to throttle body but two can be leave capped?
Like to understand what those each vacuum line does.
thanks.