348 Revs for no reason

Hi All
I had my 348TS serviced about 18 months ago and as i was driving home, i pulled away hard and the revs seemed to stick around 7k and not go down. I switched the engine off and back on and it was fine. I hardly use the car, so when i complained the Company who serviced it said it was too late.
The car drives absolutely perfect, but if i pull away fast, the revs stick again - unfortunately now, if i switch the engine off and back on, it still is at high revs - then it seems to fix itself.
The accelerator is not stuck and the odd thing is that i checked whilst it was revving in the stuck position and the carbs were closed.
Any ideas what this could be?

 

How were you able to check that the "carbs" were closed?

 

Whilst it was stuck revving I opened the boot and the accelerator cable was loose and they weren’t open

 

If the butterflies were shut, how did it get air to rev?

 

Is it possible for the butterflies to stick with the cable loose?

https://www.ricambiamerica.com/car-diagrams/ferrari/v6-v8/348-group/348-1989-1992/throttle-housing-and-linkage.html

Do those return springs on the throttle shafts break?

 

just a guess but TPS issue. ecu thinks throttle is open? same part is used on Porsche 964, they cost me $60 when I replaced mine from Porsche parts place on ebay.

 

The transverse throttle shaft (15 in diagram) rides on bushings that can get sticky when the car sits dormant. The throttle will stick, and the cable will have free play because the pedal returns but the throttles don’t. If it is sticky , use a little bit sewing machine oil or other light penetrating oil on the shaft/ bushing interface and wipe off excess.
If the shaft isn’t sticking in the bushings, check the cable routing. If still unsure if throttle plates are closed, pull off the rubber boots in front of the throttle plates and rotate the shaft (15) by hand by pulling the throttle cable. Visually verify that all linkages and throttle plates are moving in unison and returning to the stop when released.

 

Butterflies were definately closed, that's why i couldn't understand why it contuinued to rev, however it does eventually correct itself and go back to idle. I was think the TPS, but is there a way to check before i buy one (can i bypass it). I'm not a mechanic, but can do a few things on an engine. I will put some sewing oil on all the parts as well, that's a great idea. I know it's only something small, but it's atking any pleasure i have from the car

 

I had sticky throttle which stayed up around 2k sometimes during the drive and stop, found out this was probably the culprit


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Duh! Post #4!

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"Boot"? You mean the trunk-lid in U.S. terms?

I think you're hosin' us.

 

How is it you determined they were "definitely" closed? Post #7 is where it's at.

You saying the accelerator cable was loose is an indication the throttle bodies were partially open. If they are closed and the cable is adjusted correctly there should not be a lot of slack. (or they would not open all the way with your foot to the floor).

TPS could not do it. Electronically indicating a higher throttle opening than actual doesn't let more air into the engine.

 

If the idle control valves/motors are stuck fully open, they would provide quite a bit of air around the closed butterflies. However, this should not bring the engine revs up to 7k (but it might).

Justin, it is worth trying with removing the idle control motors and spraying some WD40 into them. Then, holding the motor upright, rotate it rapidly with your hand left-right. You should hear clicking from inside if the air control crank is free. If not, spray more WD40 and repeat the left-right rotation. You can also try with brake parts cleaner. Sometimes, these valves accumulate sticky gunk inside which affects their operation.

 

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Either the butterfly are actually open or the ecu thinks they are and its not reving at 7000 but it got stuck reving somewhere in the range but not idle revs after your hit 7K, Its not clear. I read it as you hit 7000 rpm then the motor was stuck revving but not likely at 7000. That where my TPS guess comes from.
If it is ACTULLY getting stuck at 7K there is no way without it ingesting air butterfly are open, unless you have some air being sucked in somewhere and at high creates a vacuum that eventually resolves as the sucking draws down. Not sure where that would happen exactly thought just thinking out loud.

First step is verify butterfly's are not stuck, remove the TB's and inspect movement and sighs of sticking, check the cables etc, lube reinstall verify then go from there.

 

A car does not rev to 7k without air. And lots of ìt..

 

Stuck choke or worn float-stop.

 

.....and it's metered air with the correct amount of fuel as well. And it's effecting both banks. Duh. I'm still of the opinion that this is a troll.

 

yes... makes sense as this makes no sense. 4 posts.. its boring in moms basement.

 

"Metered air" precisely.

So if he was talking about the throttle plate (butterflies?), viewing their position while the engine is running allows huge amounts of air to bypass the mass airflow sensor. Doesn't run very well at that point.

However, maybe his 348 has Jenvey SF throttle bodies. But I doubt it.

http://omextechnology.co.uk/page31.html

 

Perhaps a bored forum member. Careful to not bend a valve removing the air box or otherwise doing a "service".