Anyone know what it is? I want to replace my stock screws with steel ones that won't break.

Seems like M4.5 x 0.75mm to me... which is a real bastard size.
This is on my 1985 Fiero.
The screws have Philips heads.

Here, M5 x 0.8mm (much more standard) is mentioned:
https://www.fiero.nl/forum/A...314-2-117171.html#p3
I assume that this information may only be valid for later model Fieros.

I also have the option of Heli-coiling the existing holes to M5, but Canadian Tire didn't have said Heli-Coil kit stock.

Yeah, the 85-87 V6 TPS screws were made out of aluminum, verses the 88 were made from steel.

Steel screws are the best option.

------------------
fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. Beechwood interior, All original.

I got M5 x 0.8 x 25 steel socket head cap screws as per the post (no mention of model year), but was surprised when they didn't fit my throttle body.

The aluminium (or other cheap metal) screws didn't break on me, but they twisted perhaps 10° before unscrewing... so there's no chance that I re-use them.

On my previous Fiero, I drilled and tapped to #12-24, but it sucks to introduce a new US size on an otherwise completely Metric car. Furthermore, #12 screws won't fit in the TPS's mounting holes, so they need to be drilled out, which complicates future servicing.

quote Originally posted by pmbrunelle: but it sucks to introduce a new US size on an otherwise completely Metric car.

No need to worry there. It's not a completely Metric car by a long shot...

I don't know the answer for the thread size, but this can't be too hard.

Just two days ago, I replaced my TPS on my 86. The original TPS had the original, philips head screws. The replacement (BWD) had the torx screws . . . and they were threaded identically.

M5 screws do not fit in the TPS found on my 1985 Fiero; I just tried this (I only have access to my project car on weekends).

The holes in my TPS measure just 0.180" (4.57 mm) across. Since my car has only 53k miles, I suspect it may be the original TPS, but there's no way to be certain.

Since the same replacement TPS is listed for 1985 through 1988 Fieros, I suspect that the aftermarket units are made with holes large enough to accommodate all sizes of TPS screws found in V6 Fieros.

I will probably drill out the holes in my TPS to fit M5 screws, install M5 Helicoils in the throttle body, and pretend that I've upgraded my 1985 Fiero to the holy grail 1988 spec.

25 mm screw length appears to be correct; this gives 9 mm of thread penetration into my TB.

quote Originally posted by USMUCL: Just two days ago, I replaced my TPS on my 86. The original TPS had the original, philips head screws. The replacement (BWD) had the torx screws . . . and they were threaded identically.

Unfortunately, I don't have new TPS screws since I'm not replacing the TPS. I just have the throttle body out since I'm doing a throttle body mod, which I might as well share here...

For my engine rebuild, I decided that I didn't want to use the idle air manifold (and cold start injector) in the LIM for idle air purposes. Therefore, idle air would have to be directed straight into the plenum instead. So, I drilled an air passage from the inside of the TB towards the IAC passage. Then, I cut threads (3/8" NPT) in the old IAC tube receptable. I will install a pipe plug to block off this hole.

[This message has been edited by pmbrunelle (edited 03-23-2018).]