Paddcomp

Following an intake refresh last year I've found my throttle plate valve has been sticking when warm and getting progressively worse. Keeping the plate from closing and increasing the idle speed.

I've taken the plenum and TB off and using a heat gun I can replicate the problem on the bench. Within a minute of applying heat to the plate it sticks and when opened will not return to closed until cooled.
I've loosened the screws and tried to allow it to re-seat, but this has no effect. I've checked it's the correct way around, and tried another plate from another TB.
I replaced the TB bearings as per Dwayne's guide, there is 2-3mm of end float on the shaft without the plate fitted, is this normal. I have a used TB that I could replace it with, but that doesn't have new bearings, and if I fit new bearings then I could have 2 TBs with the same problem if I'm doing it wrong.

I'm open to ideas.

Brian'sIris

Not sure about the differences between your TB and mine ('85 32V), but IIRC there is a wave washer on the shaft -- between the big return spring and the throttle body -- which would tend to force the shaft in one direction (away from the throttle body), while on the other end of the shaft (where the TPS slides on) there is a circlip/retaining ring that counteracts this force. So, if there is a wave washer on one end and that circlip is missing on the other end, I imagine this could be causing your problem.

Cheers!
Brian

Petza914

Just had a similar issue on my '79 after refreshing the intake. Idle would hang up between shifts at like 2,000 or 2,200 RPM. Thouyght it was because I cleaned the throttle plate and the inside of the throttle body and the black junk I removed was actually creatinga better seal between the two, now letting some air and fiuel past the closed plate.

What I did was add a very light helper spring to give the throttle plate a little more closing force.

I also noticed that the large vacuum lines that attached to the cold-start valve were collapsing. I added springs inside those two hoses to give them some structure - springs are larger than the connectors the hose slides onto so no risk of the intake ingesting the spring.

The car has never run better.


Two hoses I'm pointing to are the ones that now have a large, open spring inside.



Shiny spring shown here is the light helper spring I installed to close the throttle plate with a bit more force. Not sure what, if anything, was supposed to be on that ball on the linkage where I connected it, but handy to find a ready-made spot.

Paddcomp

It's definitely the plate sticking and will not return even with manual help.

Glad you found a solution to your problem.

Paddcomp

I fitted a replacement throttle body, all working correctly now, returns to idle and stays there.

I'd rather have fixed my original TB, but not this time unfortunately.

Brian

M. Requin

Thanks for the followup!