aseem

Hi. I'm currently doing an intake job due to a faulty idle valve (which turned out to work when I got it on the bench. Replacing anyway)

I have done a lot of testing before hand, such as testing Temp II, TPS etc. On the TPS i found that the idle position works, but not the WOT position, so I planned to replace. The TPS is rather expensive, $350-450 depending on if its Genuine Porsche and so forth. But I also found a lot of retailers selling the Bosch 0.280.120.322 TPS for $80-90. However, every seller of these cheap ones in the US and Europe are sold out, and only the expensive ones are available, Porsche packaged or Bosch.

So why the big difference in price, and why the unavailability of the cheap ones now. Are they fake from China, and now unavailable due to the corona situation? I just get suspicious when the price difference is that great. I'm used to prices going up a few hundred percent once wrapped in Porsche cardboard, but here I'm looking at Bosch branded parts in all instances.

Can the TPS be repaired? Is there alternative parts available?

EDIT: I forgot. Just want to give a shout out to Dwayne for his excellent thread on the intake job: Dawynes intake thread:

Appreciate any feedback.

Arnljot
1980 930
1890 928 GT

Billu

Please post pics of you 1890 928GT.
I’ll sell what I don’t have even cheaper.....
Just buy from a sponsor

worf928

This is my understanding of the situation:

In the past, 928 parts that were available through the OEM (e.g. Bosch, etc.) could be purchased by a distributor and then resold to "us" and thus we used to be able to get 'reasonably'-priced parts as long as they were not totally unique to the 928.

As of a year or two ago as stock of these parts goes to zero, Porsche has been ceding control of 928 parts to their Classics division which then does two things: 1) commissions a run of new parts from the OEM and 2) requires that the OEM sell only to Porsche A.G.

Thus, parts prices will do nothing but go up over the next few years.

FredR

The problem with the WOT switch is that the soldering on the strips fails. The idle contact switch is a microswitch and rarely if ever fails- it is invariably the ancient technology of the WOT switch that fails -the soldering on the base of the contact strips fails

It is possible to cut open the switch and repair the joint but whether they can be adequately resealed to stop ingress of moisture I am not so sure.. If I get chance later I will post a picture of the one I cut open.

aseem

Ha ha, I t takes a day to fire up the boiler so i can run it out of the barn. Good catch

StratfordShark

I also replaced TPS with failed WOT as part of recent intake job on MY91 S4.

Out of curiosity opened up the switch afterwards. Very hard to do without damage to switch casing (lots of dremel cutting involved!) so I wouldn’t have wanted to use again even if I could repair it.

Replaced with new Bosch part 0280120322 which I picked up several years ago on eBay for about $85, so similar price for non-Porsche sourced part you're seeing now.

Situation has obviously changed since (I've seen same thing on Bosch fuel dampers and FPR which are now hideously expensive), but I found the eBay TPS by looking at the Bosch cross-reference guide first (on their website) and seeing which other cars used same switch. I think BMW 5 Series was one of the ones listed, the point being that if you look for the part by searching for spares for non-Porsche vehicles, you're not paying the 'Porsche premium' some parts sellers impose.

Worth a try. I'm pretty sure the TPS was not exclusive to the 928.

EDIT I was mistaken — may have been thinking of the ISV. Found this Bosch catalogue for TPS listing parts number by vehicle, and it is exclusive to various 928s

http://www.bosch-classic.com/media/b...F026T0307x.pdf

ROG100

Absolutely correct!

I have the TPS for $295 if that helps.

ddire333

I found a Lucas made version last year - Lucas SEB 182, it has worked well so far, couldn't find a Bosch one at the time and felt ok as lucas are a reasonable brand, it not a part you want to replace very often

kawi825

Good timing for this, my 84 seems to idle perfect when cold, after warm-up it goes to 1,800rpm. Need to look into it before driving season here for sure. In the fall before storage I had to turn idle screw all the way down just to get it to sit just under 1,000rpm

StratfordShark

Jenniskens' page has a write-up of an equivalent part from Hella and Huco (though I've been warned to steer clear of Huco)

https://jenniskens.livedsl.nl/Techni...7/MyTip711.htm

Banacek

Bought a Intermotor TPS 19901 some time back said it was for the 928 when opening up Bosch 0 280 120 301.on Stratfordshark other post with Bosch cross ref 0 280 120 301 BMW M5 Porsche 924 plus many more. seeing that there are only two micro switches in them what's so special. the M5 has the same air mas

aseem

Is two micro switches all there is to it? Judging from the pic at Jenniskens' page, thats all I can see. That's outrageous. Priced like a face mask in the middle of a Corona crisis. Even $85 is expensive for such a simple device, but acceptable.
I wonder why one is a closed standard micro switch and the WOT switch is an open type.

According to the WSM, resistance is less than 10ohm in closed position and open circuit after 1 degree. The WOT switch is open below approx. two third travel and 10 ohm above. Should be simple enough to make in aluminum with two micro switches.

RDON

I opened my failed TPS as a matter of curiosity. Using a bit of patience with a razor knife and a thin putty knife, I was able to open the case without damage. The glue or sealant evident on the mating surfaces was very brittle and easily flaked away.

Upon investigation I found, as others have mentioned, failed solder joints. The switches operated normally and are in as new condition, so I chose to clean and re-solder the failed joints. All functions now normal and TPS reinstalled.

Access to the TPS is obviously tedious so keep this in mind if you choose to repair versus replace. As Roger mentions, he has new units in stock.

aseem

Did you say the Intermotor unit worked for you, or did you just buy it?

FredR

Roger,

Nice pics- could not find mine that I intimated earlier.

.As I vaguely recall the input terminal for each switch is on the same side as the final elements for that function- trust I have that correct.but would not bet my life savings on it. There was something that seemed a bit strange about the layout but for the life in me I cannot remember what it was.

The antique thing with copper stalks is the WOT throttle switch commonly seen in the Smithsonian.The brassy looking box is the idle micro switch.