Felix

How do I adjust the throttle cable on a 993tt? I've read that there's a turnbuckle behind the pedal; are there any other adjusters? I haven't found anything in the archives and the PET CD isn't much help.

I've been playing around with some OBD-2 software which indicates a TPS value of a maximum of 70%; this seems a little low!

Felix

Hmm. When I have a second person fully depress the throttle pedal (engine off) and then reach in and actuate the throttle butterfly lever by hand I can still only get to 76%.

So I think I'll pull the intercooler and see if the a fully hand-opened throttle lever corresponds to a throttle plate that perpendicular to the airflow.

If yes then either the TPS is faulty or not installed/adjusted properly or the OBD-2 software is telling lies.

If no then I presume there's some sort of adjustment? But why would it be out?

Any which way I still need to take the play out of the linkage. I did see an earlier post by MOD500 here about a frayed and eventually broken throttle cable; I'll check that it looks OK.

expressmechanic

I'm having the same problem.

The TPS voltage was checked and it read 4.5 volts at WOT, which roughly translates into the 76% reading we both got.
I just ordered a new one, so when it is installed an update will follow.

Felix

I tried a different TPS and it made no difference. That seems to be normal. ACEparts_com reported the same finding, see https://rennlist.com/forums/993-turbo-forum/254544-eobd-scan-full-throttle-76-a.html

jmayzurk

Just another data point, I have the same result with my OBD2 reader when the throttle body is at its max open position.

Geoffrey

The TPS channel is a 0-5v input channel into the ECU. The TPS sensor will be limited by the mechanical stops of the throttle body for closed and open values and will change slightly depending on the idle stop, the sensor, heat, etc. It will produce a voltage somewhere around .5v at close and 4.5v at open. This is translated to some percentage that the ecu recognizes and uses in its calculations. I am not sure how the Motronics works in detail, but I believe the MAF is used to meter fuel exclusively, and the TPS sensor is used only for rate of change compensation, also called acceleration enrichment. With the Bosch systems, it is not uncommon for the TPS % value to be much less than 100% at WOT and the voltage to be near 4.5v.

To adjust the cable, there is an adjuster under the car, under the transmission plastic cover, almost to the center tunnel cover. The cable also has rod ends that can be adjusted, but the adjustment is limited and should not need to be changed. Moving the throttle pedal linkage adjuster will raise or lower the pedal only, not adjust the movement, unless the pedal is hitting the pedal stop on the pedal board before WOT.

Jussi

Geoffrey: speaking about MAF values..
what is maximum flow rating (lb/min or CFM or horsepower) which stock 993TT MAF can measure without exceeding max. voltage level (5v) ?

Geoffrey

I don't know since I have always removed them and used a pressure sensing system when I've dont MoTeC on the 993tt engines.