Throttle Bodies Show Increased Lag with Age

I rebuilt one of my TB's today with parts from a donor 0 280 750 474 unit.

The clips can easily be removed if they are pried from the curved side. Two small screwdrivers opposed pops them right off. Keep your finger on them or you'll be searching the other side of the room for the clip. Take care when removing the plastic face. Pull straight up to keep the motor contacts from being bent.

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Everything appears to be identical, at least in fit. The pickups for the pots on the new one look like they've been cheapened out a bit. Probably an engineering change. The motor housing is spring locked into the body and could probably be removed but I saw no difference between the two and the old one was in good shape. The magnets can come out and they're held in by a spring clip that is a bit tricky to get back in but can be done with just a flat blade screwdriver.

The inside of both units was clean and without any sort of lubricant. No grease or oil of any kind is inside the case. The motor itself appears to ride on a bronze bearing that's probably self lubricating. Not a lot of spinning going on in this motor so a simple bronze bearing is fine. I saw no evidence of degraded gears. An accumulation of carbon residue was found at the bottom of the motor housing cavity. I shook it out and wiped it down to remove the fine carbon dust.

The pots are mounted in the plastic face. I could see no easy way to remove the part from the face. Five tiny wires carefully soldered connect the pots to the face. The consequence is that the new plastic face should be used if the pots are going to be included in the rebuilt. That means the wrong part number will appear on the outside of the TB. If that's a bother, then perhaps a way can be devised to remove and reinstall the pots.

The pots on the old unit had obvious wear. The tracks were shiny and a visible groove existed where the pickup wires travelled.

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The pickups for the pots are tiny flexible wires on a spring arm. They rub against the pot which appears to be coated with something. The old unit showed no sign of degradation so I opted to leave the old pickup and gears in place. The pot pickups are mounted on the throttle valve pivot. In order to change the gear or the pickups, the throttle plate would have to be removed and the pivot would have to be pressed out of the housing. I decided to leave that to a future rebuild. I'm sure these parts can be removed, just not today.

The central gear just pops out. The motor armature is held in place by two torx 25 screws. Before you remove the magnets, mark them. Switching their polarity will cause the motor to either not run at all, or run in reverse. I put the magnets in upside down in one of the rebuilt units, even though I MARKED THEM. Not only mark them, but pay attention to their orientation when reinstalling.

Here's what they look like broken down:

360 unit (Bosch 0 280 750 038)
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Porsche unit (Bosch 0 280 750 474)
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I installed all the old parts into the new donor body first to see if they actually fit. The reinstall process was painless, except for the magnets. They are held in place by a spring clip that has to be pressed into place. I found a screwdriver worked just fine for this task. It was just a little tricky to find the right leverage point.

The 038 went together the same way as the 474. No surprises. Word of caution: Care must be taken when installing the armature into the motor housing. It goes in with a spring fit. If the motor contacts aren't lined up just right when the screws are tightened, the motor will bind. I found that pushing the armature down manually and then screwing it tight worked.

Once they were both together, I put them on the tester and check the results.

038-2-Right
Before: MDC 61, milliamps 2350, lag 320 milliseconds
After: MDC 32, milliamps 2635, lag 269 milliseconds

474-5
Before: MDC 27, milliamps 3040, lag 240 milliseconds
After: MDC 39, milliamps 2562, lag 321 milliseconds

I can see from the results that some losses still are present in the old rebuilt unit. As seen from the new unit rebuilt from old parts, the MDC is higher but not as high as the old unit before rebuild. The components I did not change, mainly the pot pickup, plate pivot and gear are most likely responsible.

The performance of the rebuilt unit is much improved though. It went from an MDC 61 to 32. That's better than the two working units in my car. The amps are higher from the new brushes and the lag has been reduced considerably.

I'm going to leave the matched old units in the car until I've run the 150 miles. I want to see if matching the two units solves the issue. If it does, that will be a very nice data point. If I make it to 150 miles or get a trouble code, I'll swap out to the rebuilt units and see how they fair.

 

Put another 30 glorious top down miles on the car today. Waited until dusk to avoid the heat. At the end, I even had to turn on the headlights. At first, I put on the mirror heat, thought that was the headlights. Then I remembered. This is only the second time in a nearly a year I've turned on the headlights.

70 miles down, another 80 to go before I'm satisfied the problem is behind me.

 

And as my research has proven, the rebuilding of an old TB to restore that performance comes WITHOUT a Ferrari tax.

 

I can officially classify the throttle body problem as solved. Just past 150 mile mark since the changeout.

I guess this sort of proves that throttle bodies can be tested, matched and replaced with used units instead of spending $3500 for a pair of new ones. My next stage in this process is to replace my qualified used units with two rebuilt throttle bodies using parts from new donor units. That will be an interesting test.

I've had my car just about a year and 1200 miles. In that short time, I've had numerous maintenance issues but luckily, I've been able to address them myself. Right at this very moment, the car is 100%. Of course that just means I missed something.

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Please PM me for details. Thanks.

 

I rebuild one of the old TB's, the worst one, and the results were pretty good.

 

You can easily test the accelerator potentiometer (AP) with a scanner (such as an Autel AP200) that reads voltage from AP pots 1 & 2. Sit in the car with engine off and key on, slowly press the pedal to the floor and watch the volts. The high pot should be twice the low pot in reading. So if the high pot (#1?) is 4v, the low pot (#2) should be around 2v. The variance is something like 200mV (+/-100mV) so there's room for error. The range is something like 1v-4.8v. You should see a pretty much linear rise with no flat spots or lost voltages from the low voltage to the high voltage as the pedal is pressed to the floor. If you don't see a problem with the volts being out of whack, then it's not your AP. It's something else.

 

For a car like a Porsche, changing the TB is a no brainer. They're less than $200. For the 360, the cost jumps to a whopping $1750 (at Ricambia) each and two are needed, so trying to fix a TB makes sense in the 360. Turns out the difference between a Porsche and a Ferrari TB is that the vent that attaches to the side of the TB. The Porsche has the vent someplace else.

The components from a Porsche TB can be used to rebuild a Ferrari TB though. They are exactly the same.

 

I think the car has tested them for you and they failed. It's virtually impossible to tell which TB has caused this with any standard tool. It could be one or both that's causing the problem. The typical answer is to shell out the $3k+ for two new units.

You can try to rebuild them by replacing the motor, pots and gears and hope that works. It's 1/10th the cost to do that and if you destroy your existing TB's in the process, you've really lost nothing.

 

I made the decision today to do the unthinkable. I replaced the temporary hose clamps on my throttle bodies with the permanent ear clamps. Now my engine looks right again. Probably get a code on the next drive...

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My "silencer" is some sort of no name item. I haven't found any manufacturer marks and have never seen a unit like this. It sort of looks like a Capristo but the two cans are separate from each other. It's obnoxiously loud. I'm going to pull it this summer and replace with a Ferrari sport exhaust with Tubi headers.