348 Throttle Body butterfly reset?

I had my TB's powdercoated and the set screws were removed in the process. These are usually set at the factory and not supposed to be adjusted so is there a way to get it back to factory spec? Thanks for any help on this.

 

Are you talking about the air bypass screws, or the throttle stops?

A pic would help.

 

Butterfly stops. I will just adjust them to keep them from just barely closing and see what happens.

 

This is what I found for another model:

To set idle (some random notes i got from ferrarichat forum)
Use a small piece of paper & put it between the screw and the stop. Screw the idle screw up till it just grips the paper. Remove the paper & then add one half a turn. Then set the idle at whatever level you want using the air idle screw under the TB. You shouldn't need to touch the idle screw on the throttle mechanism after that.

Thanks for the responses, however I've got an '84 QV. I found a thread from several years ago searching for 'idle adjustment' and it appears that for the idle adjustment screw.........."place a piece of paper between the screw and tab on the plenum butterfly and tighten the screw just until the piece of paper can be pulled out then tighten another 1/2 turn." It then goes on to say ......."the air bypass screw should be fully seated, then backed out 4 full turns".*

I haven't tried this default position yet, but it sounds reasonable. I believe if the car will start from this point, the plenum screw should then be used to 'fine-tune' the idle to near 1000 rpm?

Reset the idle properly when the engine is warm. Piece of paper in between the throttle screw and the stop till it just catches then + 1/2 turn. Then set the idle with the air idle screw.

It's a very small value, but the "spec" is more based on how much the idle RPM drops when the air bypass screw is fully closed -- i.e., if the engine is at 1000 RPM during warm idle (with the throttle plate a little bit open and the air bypass screw open), when you fully close the air bypass screw, the idle RPM should drop to 450 RPM IIRC. If the idle doesn't drop enough = throttle butterfly open too much.
Turn bypass screw clockwise to restrict air getting into manifold thus increasing fuel mixture.
Turn bypass screw counter clockwise to increase air or CO in the manifold to decrease fuel in the mixture.

So does it sound reasonable to set the butterfly using paper and then one half turn? Is that 1/2 turn correct for the 348?

Or

I could mostly open the bypass screw and while car is running watch RPM as I close the bypass screw fully and confirm the RPM dropped to (450?) RPM and that will tell me that the butterflies are in correct position? Is 450RPM correct for the 348?

 

Why would you get them powder coated, cant really see them with the intakes on.

Any way, you want to have the same gap between the throttle plate and throttle body bore. If I remember right (it's been a while since I played with this) that gap is about 3 thou. Once that is set, you can then play with the bypass. You will need a vac gauge to get them set properly.

 

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This is why...

From my research it looks like you may be right. 3 thou is what pops up often across several models so I will try it out. For now I snugged them until a piece of paper was difficult to slide between set screw and stops then gave it 1/4 turn. Had difficulty getting them synced using the bypass screws and two ball jars filled with ATF. I ordered a Twinmax throttle body synchronization tool and should be here Wednesday. I’m worried there may be a leak in the tubing I used that was intermittent

 

Looks great! For some reason I thought you owned a 355 and had ITB's coated..my bad..

Dont forget those MAF's are adjustable aswell. Use a multimeter. However for the life of me I cant remember the ohms, or the pins used for measuring. I have it written down at the shop in my note book. I'm sure somebody here will chime in.

 

Pins 1 & 6 factory spec is 383 although perhaps a bit lean to help emissions some say. Between 375 & 380 is what I tend to read ab out. I have mine set at 380 and temp checked cats after cooling fans kick to verify.

https://www.ferrarichat.com/forum/threads/348-maf-adjustment.167575/

 

Thanks for all the good info in this thread. I'm going to check all the plugs and connectors etc. on mine, as it was dropping power at times today, probably got wet as weather was terrible, and was also stalling at junctions, but would be ok for short while after a restart.

 

Hello everyone, I just purchased my first Ferrari, a 1990 348ts. When the car was delivered i thought it had a rough idle or what I considered rough. I also didn’t think it was cranking correctly when turning it on but I didn’t have any check engine or slow down lights so I thought everything was okay. It had its last engine out service last year. After driving for a week since delivery, I’m now experiencing RPMs increasing while I’m stopped in neutral or parked. The slow down light came on twice but went off and I felt like I had no power when I went to accelerate. Also, when the engine is warm, I’ll go to start the car and it acts like it doesn’t want to start so I hold the ignition turned until the engine fires up. From what I’ve read, this appears to be an issue with the throttle body. Can anyone confirm that or give me some thoughts?

thanks!
Andrew

 

SD lights result from:

High cat temperatures (faulty cats, improper combustion, etc)
Perceived high cat temperatures (faulty thermocouple or thermocouple ECU).

Do you know what engine management system you have? 2.5 or 2.7? There was a changeover sometime in 1990.

The unwillingness to start, rough idle, etc, sounds like improper combustion. This can be caused by fuel flow issues, spark issues, timing issues, etc. Either the engine out service didn't cure the original issue ...or made it worse. Can you remember which SD light came on?

 

Oof that sounds expensive lol do you think the engine will have to come back out to fix those items if that’s what it turns out to be? It came with a Tubi exhaust not sure if that’s worth mentioning.

it was the slow down 5/8 light. Came on twice during my last drive but didn’t stay on.

I’m not sure what engine management system I have. Would that be in my manual somewhere? I see in the manual the ignition injection system is motronic M2.5. Is that what we’re looking for?

Any thoughts to the rough idle and high RPMs when in neutral/parked? Or the loss of power when accelerating?Is that potentially the throttle body?

thank you so much for the help!

 

Not necessarily. If the 5~8 SD light came on, you can always swap minor components to see if the fault transfers.

So the timeline is...
Major done last year before purchase (Do you know by whom?)
You purchased the car, but immediately found the idle to be high and rough. What do you consider to be high?
Within a week you're finding the rpms increasing when stopped in neutral or parked. The throttle mechanism is not likely to change mechanical calibration during a drive (unless something is intermittently jamming the accelerator cable. Do you mean the throttle bodies themselves or the throttle position sensors (switches?). The switches tell the engine management systems that the throttle is wide open and the fuel management systems switch to a different profile.

Do you mean in your owner's manual it says M2.5? Assuming you have the correct manual for your car, I'm sure we can come up with some simple suggestions, depending on your skill levels. Often the problems are electrical, so you'd need to know how to operate a ohmmeter/voltmeter.

 

2.5 has one TPS (Throttle Position Switch):
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2.7 has two TPSs (Throttle Position Sensors/Potentiometers):
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So not unlike the cam sensor, in that it is wired up to both ECUs.

 

Based on the pictures in the thread, it looks like I have the 2.7 as mine has two TPSs.

timeline is accurate. I have an invoice for the shop who did the engine out service but when I called the number it went to the previous owner of the car. Not sure if it was his personal shop but couldn’t find the shop online when searching by the name.

My RPMs are increasing to around 2500 - 3000 maybe a little more when engaging the clutch going into neutral/parked or taking off from 1st without me even touching the throttle pedal. I had been doing research on these symptoms and it sounded like I needed to clean/replace the actual throttle body that has the flap that allows air in.

I’m an absolute beginner when it comes to mechanical work and never used a voltmeter but can probably get my hands on one and watch a couple YouTube videos lol

 

I forgot to mention I experienced power loss when taking off from 1st and going into 2nd and 3rd. Just didn’t feel like it was giving the acceleration power it usually did. This started happening after the SD light came on and went off. I had read about cars going into a safety mode limiting the power resulting from issues with the throttle body which further supported my hypothesis.

 

Well, that puts things in a different light. I thought you meant the revs were high by a few hundred rpm. There is an electronic idle air controller on the 2.7, but I can't imagine it increasing the rpms by anywhere near that much. It does sound mechanical. Is it possible that one of the return springs on the throttle bodies is broken. Can you check these.

https://www.ebay.com.au/itm/333790970304?

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Can you disconnect the linkages (socket and ball) under the throttle body and move the throttles by hand (externally) to see if the left/right moves in the same manner.

With the linkages disconnected, what does the throttle pedal feel like. Does it move smoothly. Maybe test it after a drive when everything is warmed up. I don't know if there are any helper springs on the pedal itself. Experts?

Try some simple lubrication on the parts you can access.

 

The first thing to check is whether the throttle cable (cable from the accelerator pedal to the throttle body linkage) is maybe partially seizing. When your engine idles at 2500 - 3000 rpm, push towards the engine on the point marked with the red line on the picture below (if the engine is hot, use a wooden stick or something). Let us know what happens.

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The 348 throttle bodies are not so sophisticated, they are very simple butterfly air valves that are only mechanically controlled (by the accelerator cable). What you have read about applies to the 20 years younger cars having mechanically and electrically/electronically controlled throttle bodies. Example:

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Thank you again for all the insight! Without having much mechanical knowledge, I’m worried if I start taking too much apart I won’t be able to put everything back together properly or risk further damage.

I checked the throttle cable while pressing the gas pedal and everything appears to be good there.

what I did do, was removed and cleaned the MAF sensor and I also cleaned the throttle body and the TPS sensor. What I found was a ton of nasty gas smelling sludge inside the tube in between the MAF and throttle body. I have a feeling that’s not supposed to be there lol.

any thoughts on what that sludge is and what might be causing that?

 

Any photos of the tube?

I've been looking through the parts manual and can't see any tubes between the MAF and throttle body

There's the idle air control system:

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This allows air to bypass the throttle bodies and MAFs to keep the engine idling when the thottle butterflies are closed.

There is the blowby system which vents oil fumes into the intakes (anti-pollution stuff).

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Or do you mean the main intake tubing?

If so, it's probably oil sludge.

 

Do you have an ordinary air filter in your airbox or an expensive aftermarket one with oil in it to catch dust particles?

 

The Idle Air Control system bypasses only the Throttle Body (TB), not the MAF otherwise it would be like intake vacuum leak.

Andrew,

At idle, the TB butterflies are practically fully closed (having only 0.02 to 0.05 mm gaps) and the engine idle speed is controlled by two "devices":

1. Bypass Screw - this is a fixed (but adjustable) opening bypassing the butterfly; it is equivalent to the butterfly being slightly opened at its idle position.
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2. Idle Control Valve (ICV) - the device #13 shown on the first picture of the above Ian's post; this is a variable opening air valve bypassing the butterfly; it is controlled by the engine ECU to maintain the idle speed at a fixed value (~1050 rpm on my Euro spec 348); the Idle Control Valve is the part that ultimately determines the idle speed based on the stored value in the engine ECU.

If you are certain that your TB butterflies are always returning to their idle position stops (fully closed), then the reason for your high idle speed is something else. With regard to setting of the TB butterflies, see the thread 348 - after engine out issue | Page 2 | FerrariChat from about post #31. Both, the butterfly stop screw and the bypass screw are set at the factory and sealed with yellow paint. If the seals look untouched on your TBs, I would not try to re-adjust them at this point.

There is a number of possibilities as to what causes your high idle speed: faulty ICV(s), intake vacuum leaks, faulty TPS(s), faults in the engine ECUs, poor contacts in the MAF, TPS and ICV connectors etc.

Your next step is to read the fault codes. See the attached document describing the procedure.

 

Oops... I mistook the throttle body for the MAF in the diagram above. It didn't sound right at the time I said it as the 355 doesn't bypass the MAF either.