Throttle hanging up

[rickshaw]

Driving around recently and I noticed the idle was hanging at around 1500-1800rpm until I blipped the throttle. I inspected the throttle linkages, cable, ISC valve etc. and here's what I found. With the linkage disconnected, the throttle shaft opens and returns normally. But with the engine running, there is friction in the shaft, due to the vacuum force on the throttle plate. I can then bring the idle speed manually to 1800, let go and the throttle return spring will not close it. Then the fun thing, shut off the engine and it closes.

So there is friction in the shaft. I seem to remember that the shafts were made with some kind of PTFE surface coating applied. Wonder if this has worn off, even though this car has only 19k miles? Also, the shaft runs on pressed in bushings, according to the exploded view illustration in the Ford service manual. Maybe these need lubrication? I'm sort of reluctant to pull the TB apart without trying something simple first, like spraying some WD40 from inside the TB to get it into the shaft holes, since there is a dust seal on the outside of the shaft, to help dissolve any carbon or other deposits that might be binding the shaft?

So just wondering if someone has had this issue and how did they fix it? Also, for someone that has disassembled a TB, I'm assuming if I remove the throttle plate, then I can pull the shaft out completely to inspect this? Not sure if I pull it apart whether I can do much as I assume there are no replacement parts available, other then maybe clean and lube the bushings and polish any roughness on the shaft. Exploded view of TB below for reference



TB exploded view.jpg

[svono50]

Pretty common issue, IMHO. I haven't really ever dug into the issue to see just what the specific cause is, because a quick blip of the throttle gets it to return to the fully closed position and brings the idle back down. I can remember doing this since I got my car back in 1991, so blipping the throttle is more muscle memory for me than anything.

I can remember early on in my ownership that I did pull the entire TB apart to inspect and shave down the throttle plate screws for more airflow (ha,ha). I remember looking at the bearings and queried a friend back in the mid-90's who worked in the parts dept of a local Ford dealer about replacements and back then the only repair method was replacement of the entire TB. So I cleaned everything up and simply put back together, where it has remained for the past 25+ years. The throttle plate is what holds the shaft in place, so just (2) screws and the shaft will slide right out, from what I remember. I never did research to see if those shaft bearings/seals were an industrial catalog item or not.

I think the issue isn't just in the shaft bind in the TB/bushings, but part of the throttle linkage on the side of the TB. I do take that side link (#13) off and put some grease in the pockets to make sure the pivots move w/o any binding, which seems to help as well. My 124K mile car shows some wear on the pivot balls, but your 19K mile example likely doesn't have any.

[Corrugated]

Have seen and heard of guys replacing the SVO throttle body with a different (newer and larger) one from a newer model Ford, 5.0 Mustang perhaps..maybe time to try that out as an option?

[rickshaw]

Thanks both for those comments. I did early on grease up the ball studs as well. Besides trying to lube the shaft, which if it helps probably won't last long, is see if I can add a throttle return spring. As far as newer TB, like 5.0, something to investigate. What I have seen is this might require an adaptor plate. Since I'm maintaining the stock IC, TB can't be spaced much closer before interfering. Those that convert to a FMIC have more freedom to convert the TB to larger diameter. Anyway, good thoughts for what I might research/change over the winter. Yes, winter is coming.

[svono50]

There have been a few different TB 'upgrades' folks have used over the years on our engines. Other than the adapter plate, as you noted, is opening up the inlet to the upper intake w/o breaching to the outside of the intake or you have to weld up the wall to get the proper through hole. There is a 60mm Ford TB, V6 application I think, that is the closest size w/o having to do too much intake modification. Like you, I am still running a stock-like intercooler, so my stock-ish TB...all have been touched by my Dremel at some point removing as much casting roughness, sharp edges, etc.

Now you got me thinking a bit, since I have (2) spare partial TB's sitting in my rafters...may need to pull them down and experiment.

[rickshaw]

Lol, that what the spares are for. OK, so I just went ahead and shot some WD40 at the throttle shaft after removing the IC. Drove it all over Sunday, no sticking. I'm just assuming this is an interim fix and the symptoms will return. So investigating the linkage some more, that link from the bell crank, for lack of what to call it, and the throttle shaft, there is maybe 1/16" of slop in the ball studs to take up before it moves the actual throttle shaft. This means, the return spring for the pedal cable and the bell crank do not put pressure to close the throttle for that last 1/16". But it does keep the throttle plate from contacting the TB bore, based on where the adjustment screw is set.

TB.jpg

So I was thinking to find some rods ends to make a new link that I can adjust to take up any clearance and make sure the throttle closes. Found some with 3/16" bore on PegasusAutoRacing, but that stock link has a center distance of only about 1 3/16". Even those small rod ends will need to be shortened. Probably worth the effort or I can just continue to shoot some WD40. Alternate is to find a threaded ball stud with tighter fit.

[svono50]

That 'slop' is why a quick 'snap' of the throttle pedal gets the idle down to its proper setting.

Little rod ends would be nice and remove said clearance (slop), but certainly a challenge for such a short link...although you could possibly go with one male and one female thread and put them together with a jam nut to get the length?? As you noted, get an oversized ball stud and machine down to fit could be another option. I am sure someone here can fully over engineer this one... :-)