Danno

"now the odd part;
while cruising on the freeway, sometimes if i let off on the gas and coast and let the engine brake, the a/f ratio first goes beyond lean as normal, but then i notice the a/f ratio 'blipping' to rich about twice per second. it almost seems like one (or more) of the injectors are not shutting off when they should, or they're sporadically turning on. has anyone heard/seen anything like this? does anyone have any idea what might be going on here?

oh also, each time the a/f blips to rich, you can hear sort of a backfiring sound in the exhaust. the whole time i'm not giving any gas and the car is engine braking."

I've noticed this A/F behavior too, on my car and on Laust's. It happens regularly as RPM drop between 3000rpm to 2000rpm regardless of gear or speed. So I don't think it's somthing mechanical like an adjustment. Might be something electronic or in the DME's algorithm. We're gonna hook up some datalogging and diagnostic equipment to figure it out...

nize

okay let me clarify. on the 951 (not on the 944 n/a, which uses a different tps);

-i've completely removed the worn tps and tried manually turning the dial lock-to-lock, it never clicked.

-i've purchased a brand-new stock bosch tps right out of the box and the first thing i did was try manually turning the dial, still no click (this is a brand-new unit, not used).

considering this part is a rheostat, how would it click?

and danno; replacing the tps fixed the problem. i suspect that when the old/worn tps heated up enough, it gave inaccurate values to the DME, which could explain why sometimes it would happen and sometimes it won't. if you pull the faulty tps and check it with a multimeter, it would have cooled down enough to give accurate readings again, which would make troubleshooting this problem a real pain.

again, i've replaced the tps with a brand-new unit and all of the problems have been solved.

nize

in my problem, it would occur at any rpm above 1500, regardless of gear or speed.

with the new tps installed, it doesn't do this at all, and the a/f ratio drops to below lean every time i let off on the gas regardless of speed/rpm/gear until the idle control takes over at below 1300rpm or so.

Peckster

Maybe they don't make a click sound when they're brand new. Whatever, it works.

Bri Bro

considering this part is a rheostat, how would it click?

Just look at the diagram in the post, it clearly shows a rheostat(pot) and a switch below it. Maybe you have a quite switch, just put a DVM across the contacts and see if it shows a short when the throttle is closed. My new TPS did click, just like the other older one did.

NZ951

We are very lucky to have your electrical experience here Brian... generally speaking.

nize

well, i think it's kinda important to confirm if this clicks or not, because a lot of troubleshooting guides mention this click, which made troubleshooting this much more difficult.

edit: i'll plan to stop by the dealer sometime this week and see if i can find out if the tps parts they have click or not.

Tom M'Guinn

As another point of reference, the alldata.com trouble shooting guide says that you should adjust the TPS with the throttle closed "until the inner stop is felt." The TPS has two circuits, as I mentioned above: (a) the "rheostat" -- i.e. pot that measures the angle of the throttle opening, and (b) a microswitch that closes when the throttle is at idle. It is the microswitch that normally "clicks" when it closes -- or perhaps is just felt as an "inner stop" on some sensors. The click seems to be more of an observed thing -- I cannot find reference to it in any Porsche publication. However, it seems to be a universal experience.... It's possible Bosch changed the type of microswitch they are using these days, since the click was not an official feature so far as I can tell... What is the part number of the TPS you have?

nize

the new one is the same as the stock bosch part number:
0-280-120-400

Asarus

I confirm the 951 tps clicks ! (old AND new)
It will click when you go from idle mode to cruising mode. As other rennlisters stated, you have to adjust it to click just when you leave the idle mode...

and my TPS is brand new from Porsche (bought 2 months ago)

nize

also, clark's garage mentions this 'click' as well;
Check the adjustment by turning the throttle toward the open position. An audible click should be hear as soon as the throttle starts to open. Slowly close the throttle until it is fully closed. Do not force the throttle closed. Allow it to close under spring pressure only. Just prior to going fully closed, an audible click should again be heard. If the click is not heard, readjust the switch.

and from what i've seen, neither the original tps nor the brand-new replacement tps makes any sort of 'click' sound, nor can you feel any click.

nize

okay how loud is this click? and does it click when you've completely removed the TPS and turn the dial by hand? can you feel this click as well as hear it? am i living in a parallel universe?

nize

asarus; would you be willing to swap your old clicking tps for my old non-clicking one? i just want to experience this click for myself.

hosrom_951

A faulty TPS would still click no matter what, when they fail they send wrong signals, but still click. You obviously have it mis-aligned: http://www.clarks-garage.com/shop-manual/fuel-06.htm

Tom M'Guinn

Now I think we are getting somewhere... The click is not loud at all -- much quieter than, say, a keyboard click. How is your hearing? Seriously. I once had a toyota with bad wheel bearings. By all accounts, the bearings would scream as a drove, but it was apparently too high pitched for me to hear. So I would drive along happily while passengers and bystanders would point and stare... Hold the TPS up to your ear in a quiet room and listen for a quiet little click when you turn it.