TPS reading at idle

nuclearpenguin · Sep 25, 2006

When logging, I've always noticed at idle, my tps sensor reads 17.5%~. Is this normal at idle, or is my TPS set wrong? I'm only asking because ive had a high idle (and some idle surge) lately and I'm trying to pinpoint it.

Thanks :thumb:

grnchevyz · Sep 25, 2006

hmm that seems high. I'll check what mine is but if I recall correctly it sits at 7% and that makes it 950rpm.

tstkl · Sep 25, 2006

its high, your throttle cable is probably off, your probably getting crappy gas milage due to your car not turing off your injectors while crusing, your high idle problems are probably caused by this, but your idle surge problems are most likely not if its simply a throttle cable adjustment problem. You might have a bad throttle cable which cannot close completely due to rust or other things. This would cause idle surge problems under certain situations.

disconnect your throttle cable from your throttle body while the key is in the accessory position and the logger is logging. Look at the tps. Adjust the tps until the logger reads 10%. Some logger programs are stupid and compinsate for this already. Dsmlink shows 0% at idle, not 10%. I think the afc does too. If your using mmcd, go for 10%. Most likely you should aim for 10%. Once the tps is set to 10% with the throttle cable off, put the throttle cable back on and adjust it until its at 10% with the gas pedel out all the way. any extra slack you give it will be gas pedal "play" in which you give the car gas and it does nothing. This might also cause your car to not open completely at wot. To check your throttle body at wot, simply (with the car off) have someone floor it, and check to make sure you can't turn the throttle plate anymore. There is a bump stop the plate hits once its fully open, so you don't have to worry about the plate turning more than 90 degrees.

and don't tell me you've searched and couldn't find it, because I've posted this more than once before....

nuclearpenguin · Sep 25, 2006

I searched for "tps idle *%" hoping to get a percentage value and couldn't find anything.

This explains why my AFC reads 0% while mmcd reads 17.5% (that REALLY threw me off). Thanks for the help

pneumo · Sep 25, 2006

On the SAFC there is a sensor check section where you can see the actual voltage the TPS is putting out. It'll be the 3rd, lowest reading on the screen. Set the TPS so you get .48 to .52 volts on the screen. Then press the throttle all the way down, it should go up to 4.9 to 5 volts.

The throttle cable should be adjusted so there is a slight ammount of slack. If it's taught it might not let the throttle close completely after the engine bay heats up and things expand.

Kevin Jewer · Sep 25, 2006

I'll post again the most efficient and effective way of adjusting the throttle cable, in case I haven't posted it here yet. The idea is to get maximum slack when the throttle is closed while still allowing full opening. The reason for this is that the cable's jacket heats up when the motor warms up and expands, effectively shortening the cable. If there is not enough slack, the throttle will open slightly. You'll be chasing your tail forever on idle problems if this is happening.

Loosen the two bolts holding the cable bracket to the manifold. Have a friend (or brick) hold the throttle pedal to the floor. Pull back on the cable jacket until the throttle is open against the throttle stop. Tighten the bolts. You now get maximum travel (slightly more even when warm, if you do this cold), and the maximum amount of slack you will be able to get given the total travel allowed by your specific car/setup.

Once the throttle cable is adjusted properly, you can then adjust the TPS properly. I've only done this with DSMlink and pocketlogger, both of which show throttle percentage as the ECU sees it. The target is 0, but barely so! I adjust it to 1, then go slowly until it just changes to 0, then stop. This will give you the maximum full throttle percentage you can get. Anything over 90% is fine, the ECU will consider it WOT. If you are too far below 0 at throttle closed, you may get short changed at WOT.

The 2g ECU needs this 0% reading, 1 at the most. Anything over that and it does not recognize the throttle plate as being closed. The 1g uses that seperate switch on the backside of the TB to accomplish this same thing, so the actual TPS reading is much less critical on those cars. The ECU doesn't make any real fueling decisions based on absolute TPS position, only relative movements (accel and decel pumps, decel fuel cut, etc).

If the ECU does not see the throttle closed signal (from the TPS in the case of the 2g), it will not go into closed loop control of idle speed. In other words, it will not use the ISC or update the long and short term ISC trims (LearnedIdleAdj and ISCposition in DSMlink, respectively). Who knows what your idle will end up at. It will be a function of FIAV, ISC, BISS, and throttle plate postions only with no feedback control.

If your logger software supports it log the idle or closed throttle switch to make sure it is "on" at throttle closed and "off" as soon as you crack the throttle plate (~2% TPS). In DSMlink, the parameter is IdleSW if I recall correctly.

With the cable and TPS set properly you can now troubleshoot idle speed control issues with some confidence that the ECU is at least now able to use feedback control, and then you have the usual culprits to address.

fulanititoo8198 · Sep 25, 2006

95GSXracer said:
I'll post again the most efficient and effective way of adjusting the throttle cable, in case I haven't posted it here yet. The idea is to get maximum slack when the throttle is closed while still allowing full opening. The reason for this is that the cable's jacket heats up when the motor warms up and expands, effectively shortening the cable. If there is not enough slack, the throttle will open slightly. You'll be chasing your tail forever on idle problems if this is happening.

Loosen the two bolts holding the cable bracket to the manifold. Have a friend (or brick) hold the throttle pedal to the floor. Pull back on the cable jacket until the throttle is open against the throttle stop. Tighten the bolts. You now get maximum travel (slightly more even when warm, if you do this cold), and the maximum amount of slack you will be able to get given the total travel allowed by your specific car/setup.

Once the throttle cable is adjusted properly, you can then adjust the TPS properly. I've only done this with DSMlink and pocketlogger, both of which show throttle percentage as the ECU sees it. The target is 0, but barely so! I adjust it to 1, then go slowly until it just changes to 0, then stop. This will give you the maximum full throttle percentage you can get. Anything over 90% is fine, the ECU will consider it WOT. If you are too far below 0 at throttle closed, you may get short changed at WOT.

The 2g ECU needs this 0% reading, 1 at the most. Anything over that and it does not recognize the throttle plate as being closed. The 1g uses that seperate switch on the backside of the TB to accomplish this same thing, so the actual TPS reading is much less critical on those cars. The ECU doesn't make any real fueling decisions based on absolute TPS position, only relative movements (accel and decel pumps, decel fuel cut, etc).

If the ECU does not see the throttle closed signal (from the TPS in the case of the 2g), it will not go into closed loop control of idle speed. In other words, it will not use the ISC or update the long and short term ISC trims (LearnedIdleAdj and ISCposition in DSMlink, respectively). Who knows what your idle will end up at. It will be a function of FIAV, ISC, BISS, and throttle plate postions only with no feedback control.

If your logger software supports it log the idle or closed throttle switch to make sure it is "on" at throttle closed and "off" as soon as you crack the throttle plate (~2% TPS). In DSMlink, the parameter is IdleSW if I recall correctly.

With the cable and TPS set properly you can now troubleshoot idle speed control issues with some confidence that the ECU is at least now able to use feedback control, and then you have the usual culprits to address.

So your saying on a 2g at idle it should be about 0,1%? Because when I had this question 10-11% was what I was suggested. Thanks just want to reassure what your saying.

Kevin Jewer · Sep 25, 2006

As I said above, this applies to DSMlink, pocketlogger, AEM, etc. I can't speak for MMCD or whatever people are using these days, TSKL covered that. If what you are using is supposed to read anything other than 0% at idle, I would make every effort to check if the ECU is getting the IdleSW made with the throttle closed, since this is the most important part. If it's a 1g you can just put a meter on that switch. I'm not so sure it's that simple on the 2g (yellow wire from TPS IIRC), never tried it.

steve · Sep 25, 2006

95GSXracer said:
I would make every effort to check if the ECU is getting the IdleSW made with the throttle closed, since this is the most important part. If it's a 1g you can just put a meter on that switch. I'm not so sure it's that simple on the 2g (yellow wire from TPS IIRC), never tried it.

On a 2G this (IPS switching) is the critical adjustment for the TPS. The specification for TPS output at idle is quite wide where the spec for IPS switch point is very specific.

In a 1G the two adjusrments are independant, so the spec for the TPS is much tighter than on a 2G. It calls for 0.48v to 0.52v.

Steve

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TPS reading at idle

nuclearpenguin

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nuclearpenguin

pneumo

Kevin Jewer

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