Throttle Position different on datalogger and AFC

[weith1111]

Looked around and only saw one thread, and the conclusion was "it doesn't matter."

Problem:

At "idle" AFC shows 0% throttle position, but datalogger shows 16%, and the IDLE switch in diagnostics never goes on.

My idle is a bit jumpy, sometimes hunting around 1500 and then setting at 7-something. I replaced the TPS a couple years ago.

When the pedal is on the floor the AFC and logger both show 100%. I'm less concerned about WOT, as it seems to be working fine, it's the never idling that bothers me.

Ideas?

Thanks in advance!

 

[q92awd]

Check your throttle cable to make sure it isn't too tight. That happened to me when I was trying to fix my 96% wot issue - I tightened the cable too much and it would no longer trip the idle switch.
At idle, the logger and afc are always going to be different because the logger will never show zero. I think it's supposed to be 7% on the logger and 0% on the afc.

 

[weith1111]

I'll check the cable, it is most likely at fault.

Is there an explanation anywhere as to why the logger always shows some TP, even if it's at 0% on the AFC and in reality?

 

[steve]

Because the SAFC scales it's output based on the min and max voltages it's seen where the ECU logs the actual output it sees. If you've searched on the subject you would know that the correct 1G TPS reading with the throttle closed on the logger is 10% which is a voltage output of about 0.5v.

Some versions of MMCd have problems displaying the IPS, what logger software are you using? The quick way to test the IPS is to measure it. You can disconnect the green wire and check that the connector is grounded when the throttle is closed and opens with a little throttle movement or with the wire from the ECU attached and the ignition on you should see about 0v with the throttle closed and 12v with it open.

Steve

 

[weith1111]

I did just find that thread about 10%.

I'm using a Pocketlogger.

Instead of putzing around with this I'm just going to check the throttle cable, ISC, TPS and BISS. One or more of them has to be out of line. I'll also make sure the idle switch is working.

Thanks for the help guys.

 

[weith1111]

Good news! Got my throttle position to show 10% on the logger. The throttle cable was fine, and was hitting the IPS when the throttle plate was shut. I had to back out the IPS a little bit as it was keeping the throttle open more than necessary. In conjunction, the TPS had to be turned a bit to bring the throttle position the rest of the way down to 10%.

The bad news:

My TPS is goners, got it to show .9k ohms at closed, but would only go to 4.4k (supposed to be at 5k) at 100% throttle, and to get the throttle position to 10%, I had to set it around .5k at closed (still went to 4.4k when open I believe).

My ICS is goners, was showing 45 or so ohms of resistance between the pins (supposed to be 28-33).

According to the logger, the car still isn't going into "idle." I wasn't sure how to check the IPS, so while the car was idling, I just unplugged it. The revs went up high, so I plugged it back in. Appears to work, and it's really a does or doesn't in this case.

Is there any problem operating the car like this, I mean I have been for who knows how long? My idle is pretty steady at 750 and it doesn't die or hunt when in neutral.

 

[steve]

Good news! Got my throttle position to show 10% on the logger. The throttle cable was fine, and was hitting the IPS when the throttle plate was shut. I had to back out the IPS a little bit as it was keeping the throttle open more than necessary. In conjunction, the TPS had to be turned a bit to bring the throttle position the rest of the way down to 10%.

The bad news:

My TPS is goners, got it to show .9k ohms at closed, but would only go to 4.4k (supposed to be at 5k) at 100% throttle, and to get the throttle position to 10%, I had to set it around .5k at closed (still went to 4.4k when open I believe).

The factory spec for total resistance is 3.5k to 6.5k. That one is still within specs.
Contrary to the misinformation on the VFAQ TPS page, your TPS doesn't need to measure 0.9k ohms with the throttle closed it just needs to read 10% on the logger. If you look up the math for a voltage divider you'll see why given the large resistance range for the TPS there isn't one TPS closed resistance setting that gives the right output voltage for all TPS.

My ICS is goners, was showing 45 or so ohms of resistance between the pins (supposed to be 28-33).

These measurements are at 68F. Your ISC coils are higher than normal but not to the point where it doesn't work.

According to the logger, the car still isn't going into "idle." I wasn't sure how to check the IPS, so while the car was idling, I just unplugged it. The revs went up high, so I plugged it back in. Appears to work, and it's really a does or doesn't in this case.

Is there any problem operating the car like this, I mean I have been for who knows how long? My idle is pretty steady at 750 and it doesn't die or hunt when in neutral.

It's not going to hard your car but it sounds like you have some issues that should be taken care of. Unplugging the IPS shouldn't cause the RPMs to soar.

Steve

 

[weith1111]

Good input (and reassurance) Steve, but what do you suggest checking at this point? I mean what other sensors could be involved. I'll replace the thermostat since it's fairly old, I have no idea what temp it is for, and it's only a couple bucks.

I'll pull the IPS again and see what happens, as well.

It was a cold morning, low 40's and on the drive to work, pulling up to a light the idle would be at about a grand for a few seconds before setting down to 750ish.

Another thing, which my car has done since I've owned it, is idle high (1000 or 1200) in neutral, while moving. As is you take it out of gear going 30mph and the revs drop, but don't go down to 750 until the car has stopped moving. I attributed this to the increase in vacuum while decelerating.

 

[steve]

It was a cold morning, low 40's and on the drive to work, pulling up to a light the idle would be at about a grand for a few seconds before setting down to 750ish.

Another thing, which my car has done since I've owned it, is idle high (1000 or 1200) in neutral, while moving. As is you take it out of gear going 30mph and the revs drop, but don't go down to 750 until the car has stopped moving. I attributed this to the increase in vacuum while decelerating.

That sounds like how it's intended to work, so what was the original question.

Steve

 

[weith1111]

That sounds like how it's intended to work, so what was the original question.

Steve

. It's just been so long that I've been dealing with weird issues that once things are "normal," it seems weird. It does make perfect sense the way it is functioning now. I would like to point out driving in reverse or in parking lots at low speeds is much smoother now; I used to have the "bucking" issue when rolling along at 5 mph. This is mentioned in the write-ups for setting the TPS correctly and idle properly, and is the truth.

It seems that every time I look under the hood I find something else that was rigged or done wrong. I've been battling a squeeky belt for a couple weeks, and just now noticed the pulley(s) that the PS and ALT share has to be on wrong. The PS belt is rubbing the timing belt cover ever so slightly, and the ALT belt looks like this: / instead of this l. It's like the inner pulley (PS) is on backwards, too close to the motor, and the outer pulley (ALT) is on backwards, too far from the motor.

So strange.

Oh well, it's getting to the time of year where it's nice to be working over a motor that's still putting off some heat. No complaints from me.