Manfred

I was afraid someone might say that. Doesn't the fact that I can still get proper idle and WOT (albeit at the wrong pedal travel position) mean that it's working though? Is it possible for the TPS to break such that WOT is still attainable?

the flyin' scotsman

Its hanging on by a thin thread and as Bill mentions it can be rebuilt but it has to be removed hence my advice to leave it until next winter when you could do a full intake refresh.

Dwayne

I'm with you, Dan. I believe if you are getting a signal from the WOT, albeit at 99% pedal travel, it is still functioning. I don't have a lot of experience with failure modes or partial failure of the TPS but it might be worth some additional adjustments to see what you get. In order to get more out of the pedal travel (down to about 75% travel) without disabling the idle switch, you will need to add slack to the cable that runs from the linkage at the side of the plenum (in your picture above) to the throttle plate. Also, I notice from your picture that the gap in the crimp ring and the plastic cable nut seems too large. It looks like the cable housing is not fully seated in the plastic adjustment nut. Sometimes when the cable is disconnected, the cable sleeve comes out of the plastic adjustment nut and doesn't seat all the way back in when connected up again. This happened on mine as well. I simply pulled on the cable housing maneuvered it so it fully seated. It should look like the cable at the bottom in your picture. Making that fix alone will introduce slack into your cable.

I'm not familiar with the 5-Speed cable set up but you need to find which of those cables is the one that feeds the throttle plate and add slack to it. Then go back to the accelerator cable and take out some more slack until you get to the 2/3 or 3/4 pedal travel desired. JMHO.

Manfred

Yeah, that's procedure I've followed by for some reason it's not getting me the results. Part of the problem may be that I've fully adjusted the cable from the accelerator pedal (until adjusting bolt comes out of firewall--then I thread back in just one or two turns). With maximum adjustment on that cable (still seems a little slack) I've then tightened up the cable to the throttle mechanism as much as I can while still retaining reliable idle switch function. With those adjustments I am getting WOT but basically only with the pedal all the way to the floor.

Does that suggest that maybe I need to somehow take more slack out of the throttle cable (maybe where the actual cable gets crimped and then threaded onto the ball)?

I pulled the ball out of the socket and played with this but it won't seat in any further. I tried to pull the plastic adjustment screw from the quadrant to more fully investigate but I haven't figured out a way to press in all four retaining clips at the same time (I think in your intake R&R post there were only two retaining clips on this part? My '91GT has four so I guess I need to get two small pliers at right angles in there or something--not easy). In any case, it doesn't look like getting more slack in this cable would help as I'm maximally tightening the cable to the accelerator and still have slack available at the cable to the throttle body...

I haven't examined this closely but how does the quadrant function. Does the throttle cable travel more, less or the same for a given distance of accelerator cable travel? If they travel the same distance then I'm not sure adjusting the accelerator cable any more would make any difference to my situation since I've adjusted all the slack out to the point where any more slack taken out makes the idle switch not work.

If on the other hand there the throttle cable travel in greater than the accelerator cable travel by some factor then I could see how further adjustments on my accelerator travel might give me the result I'm looking for. Does that make sense to anyone but me?

Bill Ball

It's better not to have breaks in the adjuster plastic housings where you have them, but as long as the adjustment still is possible, that's OK.

That the TPS WOT trips at all is good news. When the solder joints inside the TPS crack, the trigger point moves up and eventually fails completely. Even new ones don't always seem to trigger WOT at 2/3rds to 3/4ths throttle, so eliminating as much slack as possible without taking the throttle off the idle stop is important. And as Dwayne mentions, the pedal travel limits the maximum opening. So, it's best to take all the slack out with the firewall adjuster first.

Manfred

so it sounds like this is what's happening, or as Malcolm said:
I guess what I've accomplished is as good as it's going to get for now and a TPS replacement during a full Intake R&R ala Dwayne is the next step--as suggested, I think that'll be a next winter project although I didn't park my shark this winter--no snow or salt in Charlotte (or at least only a couple days out of the year).

IcemanG17

Dan
It appears your quadrent to throttle body cable is towards the tight side (using both my 928S4's as a guide)...so its possible the WOT is dying or near dying..... Both of my 928's get WOT around 3/4th throttle (pedal).... Since it is working, but with a heavy foot your still fine..

When I first got my 88 automatic it DID NOT have WOT (loose throttle cable that Bill fixed)....which just means it looses out on the WOT enrichment tables in the LH....so it stays with the standard "Cruise" maps in the LH which use the O2 sensor and is constantly in search of 14.7 AFR....so it costs you a little HP and causes the engine to run hotter and high load (Bill had this problem in an ORR and nearly overheated due to it)...

So my long winded advice is DRIVE ON....its working...then when you have some planned down time, maybe next winter...to a "Flap-O-Dectomy" and replace everything under there.....

Manfred

That's my plan at this point. Thanks for everyone who has helped me get this far. TPS is will be on the list if/when I decide I can handle an intake R&R.

Melo928

This was a very helpful thread, I had exactly the same situation than Brian in my -84 S automatic. WOT was working only when pedal was leaning on kick-down which made car very on/off-style to drive. I could feel that car was on lean&retard side in accelaration, and chased vacuum and fuel pressure problems..

Just took slack of and car is a totally different to drive, I can feel WOT coming on and gearbox is much more responsive while dropping gears more eager without jumping on kick-down.

Every 928 owner should check this