500E throttle actuator removal

[seacoast_benz]

I have the 500 parked for a few days for miscellaneous downtime and minor servicings. Thought that this might be a good time to take a look at the throttle actuator.

It's not an urgent item -- we just put a few hundred miles of long-distance freeway driving on the car last weekend, and it still runs letter-perfect. But many owners report that their TBA began to get sick at about the 60K to 80K range, and our car is coming into the lower end of that now.

I have security Torx bits to open the TBA casing up for an inspection, but what isn't clear to me is how to remove the TBA itself. The airbox and filter assembly comes off trivially.

The MAF sensor assembly is right there on top of the TBA, and the cable on its side detaches easily. But I can't see how the MAF is attached to the TBA, nor can I see how the TBA bolts to the intake manifold.

I've found comments here that unbolting the TBA from the M119 engine is pretty trivial, but I've also found a lot of comments to the effect that a dealer will charge four or five hours of shop time (excluding the cost of a new TBA).

s/b

[seacoast_benz]

Hey, replying to my own post, but in a good cause. Don't want anyone to waste time on a reply where none may be needed!

I've found what looks like the MAF-to-TBA connector, two screw clamps going around the MAF lower throat. The MAF data cable had been lying over the screws, and I wasn't able to see them until I got it out of the way.

I can also see one Allen head partially blocked by the MAF, which is probably part of the TBA to manifold connection.

Now all I have to do is to get these screw clamps off. Not a lot of room to work with in there! I have a couple of right-angle ratchet adapters that regularly save me, but I don't think they are going to fit in the space available. Maybe the tool store has a right-angle Phillips key that would do the job.

s/b

sb,

The MAF slips into one side of a rubber connector (collar) and the the other side fits over the throttle actuator. Both are held tightly with the large clamps. If you loosen the clamps, you can pull the MAF straight out. Over time the rubber hardens and you will probably rip it apart when you pull the MAF out. The actuator is held down with 4 bolts. After removing the bolts you can work it out of the upper intake by turning it sideways and swearing a lot. To replace you will need the manifold to TA gasket and a new rubber TA to MAF collar.

My actuator is fine after 114K miles even after I pulled it out to replace the rubber crankcase ventilation hose that connects to it on the bottom rear. I wouldn't mess with it unless I had to. The more the wires get moved around the more chance for problems. The wire bundle connected to mine was still nice and pliable with no crispy parts.

Randy
'94 E500

[seacoast_benz]

Originally posted by Randall Grubbs
sb,

The MAF slips into one side of a rubber connector (collar) and the the other side fits over the throttle actuator. Both are held tightly with the large clamps. If you loosen the clamps, you can pull the MAF straight out.

Your choice of words is superb, Randall -- "if" I loosen the clamps is the question of the moment!

I spent about 45 minutes trying to get an angle on the clamp screws with no success; I tried everything in my box of tricks. Went out to buy an offset screwdriver, and then found that there isn't enough angular room to move it once it's on the first screw.

Over time the rubber hardens and you will probably rip it apart when you pull the MAF out. The actuator is held down with 4 bolts. After removing the bolts you can work it out of the upper intake by turning it sideways and swearing a lot. To replace you will need the manifold to TA gasket and a new rubber TA to MAF collar.

Roger wilco. I am prepped with part numbers. And I am well familiarized with swearing a lot after my last bit of 500E wrenching, the change of transmission shifter bushings :-)

My actuator is fine after 114K miles even after I pulled it out to replace the rubber crankcase ventilation hose that connects to it on the bottom rear. I wouldn't mess with it unless I had to. The more the wires get moved around the more chance for problems. The wire bundle connected to mine was still nice and pliable with no crispy parts.

I do have to say that perhaps discretion is the better part of valor on this one. The experience of other owners suggests that TBA failure mode is slow and well telegraphed, instead of being an instant vehicle stopper. That is good to know. An instant stop, if it ever happened, could leave us inconveniently stuck in a one-horse town somewhere, as we drive the 500E primarily as a distance runner. (It's much too nice to use as an urban commando. I have other cars for that job.)

And this TBA unit seems to be working brilliantly, plus, all of the wires and hoses under the airbox look to be in fine shape. Very flexible, no discoloration, no cracking. I may put a bit of nonmelting synthetic grease around each hose terminus just to be cautious, but that's all I would think that it needs for now.

The one rationale for having the TBA out is that if it is starting to get sick, this month is my last shot to have it replaced under Starmark. Given that it's a spendy piece of kit, I may be willing to put in the time to remove and open and inspect. My assumption is that if there were severe wire cracking visible inside, MBUSA would ante up for a new unit.

s/b

[seacoast_benz]

Originally posted by Randall Grubbs
sb,

The MAF slips into one side of a rubber connector (collar) and the the other side fits over the throttle actuator. Both are held tightly with the large clamps. If you loosen the clamps, you can pull the MAF straight out.
'94 E500

Note to others in the same boat:

I cursed for a long time trying to figure out a way to get torque on the screws of the boot clamps. From above, it's impossible.

Finally realized that there is a path in from the side, if the clamp screws are on the front of the MAF throat the way they are on mine. Coming in laterally from the vicinity of the fuel rail, a nine-inch slotted screwdriver can reach and turn both clamp screws.

I now have the clamps so loose that they rotate when touched by the screwdriver. The MAF itself rocks back and forth and rotates about 5 degrees, but hasn't released just yet.

s/b

[seacoast_benz]

Okay, taking notes as I work, for the benefit of others doing the same job:

The MAF assembly does come loose once the two clamp screws have been backed off sufficiently. I had already removed the data cable coming off one side of it.

I had to rock it back and forth for a while to get the MAF loose inside the boot, and then took a pry bar and very gently prised up at the rear, using the rear arch of the intake manifold for a leverage point. The MAF came loose smoothly and cleanly, and the boot looks pretty good for its age and mileage -- I could certainly re-use it if I were so inclined. Apparently it's rare to find them this well off, so plan to have a spare available.

No issues pulling the MAF clear after that. But you will want to have a shop-vac ready to get down in there immediately. This area around the TBA to MAF connector apparently collects dirt and sand, and you won't want any of that inside of an M119 engine. I vacuumed very thoroughly and cleaned dust off of all hoses and wires before continuing.

The TBA is held down with four 5mm allen bolts. The left rear as you face it is the only one with a small tool path issue -- a hose runs immediately above it. Instead of pulling the hose, I used a wobble joint. None of the bolts presented any trouble.

A small (vacuum?) line, translucent plastic, runs above the TBA from front to rear. I had to disconnect this before considering TBA extraction, and since I can't even see the front of it, I pulled the rear. My large hand barely fit behind the throttle linkage at the back to pull it loose; I hope I can get it back on! Make a note so that this won't get forgotten at reassembly time. It's unobtrusive once out of the way.

Still have to figure out how to get the throttle pivot off the side of the TBA. Hmmmmmm. Back to the garage!

s/b

[seacoast_benz]

OK, I'm stuck. Been through the archives, can't find anything, so we're breaking new collective ground here for the MSShop knowledge base.

The TBA is loose from its bolt mounts, but it is fastened to three other assemblies:

(a) In back, there's a heavy hose, I presume for vacuum. I can't see how it fastens to the TBA. The other end of the hose is up above the TBA and easy to pop free -- but it would be easier to move and handle the TBA if the hose were loose at the back, and out of the way.

(b) There's a heavy cable assembly that comes off the top of the TBA, routes across to the wire loom that goes through the firewall to the computer compartment, and has a modular plug there in the compartment. I can't see any easy way to remove the cable at the TBA body, but I also can't see how that plug can possibly go through the firewall opening.

(c) The throttle pivot on the side of the TBA is connected to the linkage by a ball-cap mechanism, and the pivot is also connected to the (intake manifold?) by a return spring. I think I could get the spring off without too much trouble.

Any leads?

s/b

[seacoast_benz]

Continuing the troublesome saga:

The throttle pivot is off; gentle torque with the flat of a slot screwdriver blade popped the cap free from the ball.

The spring on the pivot was gently maneuvered loose and laid flat on the intake to prevent it losing its moorings on the far end. (You will want LONG needle-nose pliers for this!)

The TBA itself is still not out. I'm beginning to see where the 4.5 hours of quoted shop labor for a TBA replacement come from!

I found a couple of accounts in the archive which make it sound like a TBA pull on an M119 engine just involves some minor gymnastics with the unit. I have no idea which engine those posters were working on, but it's not this one! Either that, or they have some amazing topological maneuvering mojo which greatly exceeds mine.

I am no stranger to wrenching in tight spaces, but this is a tough puppy. What it looks like the drill is is that the front of the TBA has to tip up, and then the right side, which is bulkier, has to rotate down and to the center to have enough room to come out.

There are two metal lines in front of the TBA -- I had to take out both line mounts to have even a prayer of moving the TBA around. One of those involves a 19mm nut that is way down in there. For anyone who is planning the job -- you will need an extra, extra deep 19mm socket, or else will need a 19 crowsfoot plus a wobble and an extension to be able to get at the bloody thing.

That leaves me with two obstacles still: the cable bundle, which doesn't seem to come off, and the breather hose at the back of the TBA.

The hose is pretty obviously going to have to come off, but it is *hard* to get to it to apply outward force to slip it off. The hose itself is heavy stiff rubber and not easily manipulated.

Given how hard it is to get to, and that it is something like a $10 item from PartsShop, I may just remove it destructively and put on a new one. Especially when you consider that replacing just this hose in later life of the vehicle would require loosening up the TBA, which is a tough bit of work.

[seacoast_benz]

OK. The TBA is out of its nest.

Before anything else, for the convenience of anyone else who may have to suffer through this job, let me mention a critical point that is not mentioned in any of the dozens of other posts here about TBAs:

The rear breather hose on the TBA is *not* a slip-on over a barbed connector, although you could easily be fooled into thinking that it is by its appearance, and although it *is* a slip-on on the other end of that hose.

It's actually held on to the TBA by a squeeze clamp hidden down around behind. And yes, you can get the clamp and hose off -- I just did -- but you are going to have to rotate the TBA up on the left side simply to get a rough visual on the situation, and to be able to get a tool on the squeeze clamp.

If you don't own a set already, let me commend to you the extra-long needlenose pliers sold by Harbor Freight. As with anything from Horror Fright, don't expect to pay much, and don't expect them to last -- these are six months old and already in worse shape than my 20-year-old Craftsman short needle pliers -- but for some jobs, they are great.

Second critical note: you should *not* be doing a TBA removal without a powerful shop vacuum around. I have a real monster of a vac, and I'm glad to have it.

Removing the TBA is going to leave behind a lot of stirred-up dirt. Also, pieces of the TBA-to-manifold gasket will probably come off. Mine stayed mostly in one piece, but one chunk broke off and was lying beside the intake opening. The gasket is a hard phenolic resin type material, and I think that even a small piece of it would greatly disagree with the engine's digestion on restart.

So, *immediately*, before doing anything else, as soon as the TBA is free, remove all remaining gasket material, get the vacuum nozzle down and into the intake (you will want a point-tip nozzle), and clean up the entire area inside and out, rigorously. Then cap the intake with foil or stuff a clean shop rag into it to prevent any further contamination.

s/b

[seacoast_benz]

Final removal note for people doing this job in future:

Once the TBA is off of the manifold, there is the matter of the data cable which runs off of it (and which is not removeable) through the firewall to the computer area.

The cable does disconnect on the far (computer area) end, and it has a hefty plastic plug on it. It is not clear visually whether or not one can get this through the firewall opening to remove the TBA from the car without disconnecting other cables.

I did successfully squeeze the head through the firewall without damage. You will have to unbolt (one bolt) the plastic wire loom/frame, which is in two pieces, that surrounds the several cables as they go through the F/W. Fully remove both pieces of the loom.

It may not look like you can move the other cables sufficiently as to allow the TBA cable head to go through, but I found you can get it done.

That's it!

The job took me many hours, but knowing what is detailed above, it could probably be done in 2-3 hours with the right types of tools. Without those tools, it may be impossible.

s/b

So sc_b,

Now that you have it out what next? Are you going to replace it? The only reason I took mine out was to replace the breather hose that connects to it. I only took mine out enough to get to the hose as not to move the cable around too much.

Btw, that plastic frame at the firewall was the part that gave me fits when I tried to put it back in around my new engine wire harness. It was difficult to compress the new bundle enough to get that frame back in.

Randy
'94 E500

[seacoast_benz]

Hey, Randall, I owe you a word of thanks for having posted the breather hose part numbers in your article about doing the wire harness job.

My rationale for removing the unit was to inspect inside the TBA case, and to check inside the insulation of the cable bundle for cracked wiring. About to roll out of Starmark here, and if needed, I would rather them pay for a new TBA than out of pocket.

In this case, the unit is in *excellent* condition. I thought it must have been a warranty replacement, even though there is none listed on the MB-Net for this car, but no, it's the original 1993 unit.

I posted my results on this older thread, since it has photos by Neil of what a heat-damaged TBA looks like:

500E throttle-body- heat killed

The unit that Neil opened had visually obvious solder resin runs, and cracked wires on the circuits inside of the case.

This one has none of that going on. The only explanation I have is that this particular car seems to be the coolest-running 500E I have ever heard of -- it has never shown engine temps over 90C even in the hot high desert at 115F outside -- and since heat seems to be a big culprit in breaking down wire insulation and baking the solder joints, less heat is a good thing.

I have electrical contact enhancer liquid from CAIG Laboratories in the workshop, and I'm going to apply it in small quantities both inside the TBA case, and on the exterior cable terminations.

Still not sure if I should put a light synthetic lubricating oil on the shafts of the rotating parts inside the TBA body. They all seem to turn freely, but then again they're ten years old without having seen daylight.

s/b

[Gilly]

The gasket between the actuator and intake manifold isn't resin or anything like that, it's green colored PAPER. That's what heat and torque do to it, makes it brittle and shiny looking. Be sure to order a couple of then for reassembly, the first time you will no doubt goof and ruin one. They say you're supposed to replace the 4 bolts as well.
It's a good idea to go ahead and order the breather tubes as well, as the are usually too brittle (no matter how nice they seem) to allow an easy reinsertion into the "Hell Hole" as most mechanics who've done this job on a 119 call the chasm that the throttle motor fits into. Spraying a little soapy water onto the tube will help keep it from getting yanked off when trying to reinsert.

Gilly

[seacoast_benz]

Originally posted by Gilly
The gasket between the actuator and intake manifold isn't resin or anything like that, it's green colored PAPER. That's what heat and torque do to it, makes it brittle and shiny looking. Be sure to order a couple of then for reassembly, the first time you will no doubt goof and ruin one. They say you're supposed to replace the 4 bolts as well.

I just picked up a replacement at the local dealer -- normally I'd get it via the PartsShop, but it's inexpensive, $3.50 or something, and I was wanting to get the car back on the road today with no shipping delay.

You're right! Green paper. The one that was in the car is hard and brown and brittle, scarcely recognizable as having been paper once. I'm glad to have that replaced.

We'll see if I can manage the re-install with just the one gasket.

As for the bolts, I hope they aren't torque to yield or anything like that. I'll inspect carefully, chase the threads and apply a drop of light oil, then make sure they hand-thread all the way down.

It's a good idea to go ahead and order the breather tubes as well, as the are usually too brittle (no matter how nice they seem) to allow an easy reinsertion into the "Hell Hole" as most mechanics who've done this job on a 119 call the chasm that the throttle motor fits into. Spraying a little soapy water onto the tube will help keep it from getting yanked off when trying to reinsert.
Gilly

I'm not looking forward to wrestling with the breather again. Will let you know how that one goes.

s/b

[Gilly]

IIRC, the bolts are "microencapsulated", which is like a fancy threadlock material on the bolt tips. It's usually a greenish color. I believe that's why MB wants to have the bolts replaced. I wouldn't sweat it, but instead of using oil on the threads, I'd put a drop of threadlock on the threads instead.

Gilly