Df250 Throttle jumps

[Bob Gariepy]

Throttle goes from 655rpm to1045rpm with just a touch on the throttle. Cable at motor is smooth while advancing but then the rpm jumps up. Cable lever at motor travels about 3/8" then rpm jumps up.
Any Ideas or just a touchy throttle that I have to live with.

[Harper]

So what you're experiencing is off idle, the RPMs jump right up to 1045. I think that it's not that unusual, if you have the cable controls. You can feel the notch where the cable starts to pull open the throttle, and it is pretty sensitive right there. I can open the throttle to 800-900 RPM now, but it takes a very light touch to do so. I have to kind of tap the throttle lever open. The same thing happens in reverse order coming off plane and throttling down to no-wake speed. The throttle will hit that little notch and usually close on me, causing me to have to nudge it back up to around 1200-1300 RPM. The drive-by-wire system probably eliminates all that.

[redlowrey]

Could be what Harper is saying, but check the throttle position sensor and see if the signal voltage jumps up quick when you just touch the throttle, that’s what it sounds like to me.
The computer will think that the throttle has been opened quick and it will change the duty cycle on the iac valve and increase pulse width on the injectors increasing rpm.

[Bob Gariepy]

My thought is the TPS, will check that first.

[Harper]

Could be what Harper is saying, but check the throttle position sensor and see if the signal voltage jumps up quick when you just touch the throttle, that’s what it sounds like to me.
The computer will think that the throttle has been opened quick and it will change the duty cycle on the iac valve and increase pulse width on the injectors increasing rpm.

Interesting...... I didn't consider that the engines (except maybe the drive-by-wire units) would have a throttle position sensor. Of course, they do, else the ECM wouldn't have any input as to throttle position. It's apparently built in to the throttle body. Is it adjustable in any way, or would the whole throttle body have to be replaced in the event of malfunction?

[Murray]

In my service manual (2009 DF90A) in bold letters “Do not try to adjust or remove any of the throttle body component parts” Goes on to say “If out of specification… replace the throttle body and recheck” So yes if TPS in NFG then throttle body must be replaced. On my engine at least.