Idle and TPS question.

[1LE]

First off, I'm *very* familiar with the BISS backing out issue, and mine is actually RTVd into place due to that.

So, no, it's not backing out, but my idle is creeping high anyways. Since it's been doing so, I've also noticed that my TPS no longer reads 0% at idle. it's bouncing around between 0.5 and 1.5% on my AFC during normal driving, and the amount that the idle is high seems to correlate with how high the TPS % is... So, that's my leading candidate...

I've verified that there are no cable issues, the throttle snaps solidly to the fully closed position. There have been no changes to the throttle area, nor the BISS.

Questions are:

- What TPS % do you all see at "idle", and on what device? My thought is that when the idle position is achieved, the ECU should go to 0% (even if it thinks otherwise for some reason). Side note, one ECU/tuning guide I found claims that I should see 10% at idle and 100% at the ECU and 0% idle and 100% WOT on the AFC. I did a quick comparison of ECU vs. AFC in the driveway and found that "idle" currently is 0.5-1.5% on both the ECU and AFC (exactly mirroring each other) and that WOT is 90% on the ECU and 100% on the AFC...

- Would a vacuum leak (or post MAF air leak) somewhere confuse the ECU into not seeing true idle?

- I'm thinking I'd like to pull the TPS connector to do the resistance checks, but I can't figure out how the clip-on connector works. How do I remove that connector without breaking it?

 

[Ludachris]

Can a 1g Tps be used in a 2g if the idle switch is simulated in dsmlink?

I wouldn't be the one to listen to on this, but I think DSMlink still needs the signal to simulate, which it wouldn't have with a 1g TPS. I could easily be wrong though.

 

[RocCitySlayer]

Oh ok. Im asking because I just got ahold of a better 1g TB it came with the TPS and IAC. I was hoping I could use the TPS

 

[steve]

Just went for a drive on my lunch, drove to the store on city streets. When I got to the store the water temp was at 219. The RPM was at 1900, STFT was something like -18, the TPSVolts was .73, the front O2 stopped cycling and was stuck at .96. Not sure what else I should have looked at. I got out and tightened the BISS screw in all the way and it didn't change the idle at all. Turning it the other way didn't do anything either. By the time I got back to work the RPM was 2300.

Chris, I'm sorry to say I don't think the BISS is the problem. It doesn't sound like the FIAV or ISC were either.

The question seems to be were is the vacuum leak that gets worse as the engine gets hot?


On the subject of simulating the IPS, DSMLink can do so solely on TPS voltage. I prefer a working switch, either a 1G IPS or a 2G TPS.

 

[Ludachris]

Chris, I'm sorry to say I don't think the BISS is the problem. It doesn't sound like the FIAV or ISC were either.

The question seems to be were is the vacuum leak that gets worse as the engine gets hot?


On the subject of simulating the IPS, DSMLink can do so solely on TPS voltage. I prefer a working switch, either a 1G IPS or a 2G TPS.

Wouldn't a boost leak test bring that to light? Maybe BOV diaphragm? It's a newer BOV and these symptoms have existed long before I swapped in this BOV. I don't know what else would cause it to do that once it gets hot.

 

[Tyeler18]

Just went for a drive on my lunch, drove to the store on city streets. When I got to the store the water temp was at 219. The RPM was at 1900, STFT was something like -18, the TPSVolts was .73, the front O2 stopped cycling and was stuck at .96. Not sure what else I should have looked at. I got out and tightened the BISS screw in all the way and it didn't change the idle at all. Turning it the other way didn't do anything either. By the time I got back to work the RPM was 2300.

To start, your temps are starting to get mildly warm. Warmer than I'd like to see on any dsm.

2nd- TPSvolts is off slightly. It should be turned down to .63V. Does it stay at .63v when cold?

3rd- That STFT is WAY off. It's running super rich (negative means it's trying to remove fuel). A torn diaphragm in your FPR, bad o2 sensor, stuck open injector all could be causing this. Do you have a fuel pressure gauge? Or a noid light?

4th- The fact that your o2 went dead leads me to believe you very well could have a dead o2, however, it could just be so rich (judging by the -18 STFT) that it isn't even cycling back to lean anymore. Your rich condition may have also started to take out the o2 sensor with it.

It's hard to say what it could be, but you definitely need to find out what your rich condition is caused by. Definitely not a vacuum leak as you'd have positive numbers.

 

[phr0st]

I have link set to 850 RPM, and that's what it idles at for a little while before I do much driving. So should I adjust it when the RPM is stuck at one of the higher levels? Before I removed the FIAV and fixed the boost leaks I remember closing the BISS completely one time when the idle was stuck up at around 2k and it didn't do anything. I'll try it again though today when I get home, as the idle is usually pretty high by that time.

It seems there are about 3 levels depending on how hot it is outside and how much driving I've been doing. After a short drive in warmer weather it moves up to around 1100 and sits there for a little while. Then, after more driving it will jump up to around 1600 all the sudden and stay there. If it's really hot it will jump up to 2k and hover there while driving. At that point I turn on the A/C, which seems to drop it back down to about 1k with some erratic jumps every so often. There is no surging, just sticking at a certain RPM. The stock water temp gauge stays the same but I think the car runs a little hot, up around 215-220 when it's really warm out.

I had exactly the same issue for the past 4 months with my car. I replaced everything I could think of, rebuilt the tb, and still the car was having a high idle at any coolant temp over 200 degrees. I BLT'ed the car multiple times and fixed every leak i could find. I finally found my issue and it turned out to be the gap between the throttle plate and its bore. Other things to check would be intake manifold gasket. Hard to see if it's leaking from the bottom and EGR gasket. Do you have a wideband? If so what are your AFR's at idle and what are your AFR's when your car switches to open loop(no 02 feedback)?

 

[Ludachris]

To start, your temps are starting to get mildly warm. Warmer than I'd like to see on any dsm.

2nd- TPSvolts is off slightly. It should be turned down to .63V. Does it stay at .63v when cold?

3rd- That STFT is WAY off. It's running super rich (negative means it's trying to remove fuel). A torn diaphragm in your FPR, bad o2 sensor, stuck open injector all could be causing this. Do you have a fuel pressure gauge? Or a noid light?

4th- The fact that your o2 went dead leads me to believe you very well could have a dead o2, however, it could just be so rich (judging by the -18 STFT) that it isn't even cycling back to lean anymore. Your rich condition may have also started to take out the o2 sensor with it.

It's hard to say what it could be, but you definitely need to find out what your rich condition is caused by. Definitely not a vacuum leak as you'd have positive numbers.

I'll look into the cooling temps when the idle is fixed. The TPSvolts is at .63 when cold and up to operating temp. The injectors are fairly new and this problem was around before they were changed. The FPR and O2 sensor could be the issue. No FPR gauge or wideband. I'll likely change the O2.

 

[Tyeler18]

I'll look into the cooling temps when the idle is fixed. The TPSvolts is at .63 when cold and up to operating temp. The injectors are fairly new and this problem was around before they were changed. The FPR and O2 sensor could be the issue. No FPR gauge or wideband. I'll likely change the O2.

I thought you said that TPS volts was at .73V? Mis-type?

The injectors themselves may not be the problem, but there could be a short to ground or one injector driver that is not ungrounding the injector causing it to constantly spray. Both *should* cause a poor start condition though, so unlikely.

Pull the vacuum line off the FPR, is there fuel in it? Good indicator of a bad FPR.

O2 is a starting point. I didn't see, does it idle normal on cold starts? If so, it's more than likely something occurring doing closed loop operation. O2 is ignored until closed loop, so it could definitely be your problem.

One more is a possible bad MAF. Not nearly as easy to test without a proper scan tool though.

 

[Ludachris]

I thought you said that TPS volts was at .73V? Mis-type?

The injectors themselves may not be the problem, but there could be a short to ground or one injector driver that is not ungrounding the injector causing it to constantly spray. Both *should* cause a poor start condition though, so unlikely.

Pull the vacuum line off the FPR, is there fuel in it? Good indicator of a bad FPR.

O2 is a starting point. I didn't see, does it idle normal on cold starts? If so, it's more than likely something occurring doing closed loop operation. O2 is ignored until closed loop, so it could definitely be your problem.

One more is a possible bad MAF. Not nearly as easy to test without a proper scan tool though.

TPSvolts start out at .63 at startup and up to normal operating temp. When the idle starts acting up and temps get a little higher it jumped to .73. It starts and idles fine. This is speed density so no MAF. I'll check the FPR.

 

[Tyeler18]

TPSvolts start out at .63 at startup and up to normal operating temp. When the idle starts acting up and temps get a little higher it jumped to .73. It starts and idles fine. This is speed density so no MAF. I'll check the FPR.

The TPS voltage shouldn't change ever. It's a potentiometer so the only time the voltage changes is when the throttle plate moves. It'd be an odd coincidence that a known good TB would start locking up when it gets hot.

When it's warm and idling poorly check the tension in the throttle cable. Also try closing the throttle plate by hand. That should always sit at .63V at idle no matter the conditions. Something is messed up there. The TPS itself could be malfunctioning when it gets warmed up (I assume you swapped your 4 pin TPS onto your 1g TB?).

The only other *possible* cause would be a voltage spike across the reference wire only when it gets warmed up. Which would be rather unlikely. Your idle problem, I'd put money on, lies within whatever is causing the TPSvolts to increase, however, your fuel trims need to be fixed as well.

 

[Ludachris]

The TPS voltage shouldn't change ever. It's a potentiometer so the only time the voltage changes is when the throttle plate moves. It'd be an odd coincidence that a known good TB would start locking up when it gets hot.

When it's warm and idling poorly check the tension in the throttle cable. Also try closing the throttle plate by hand. That should always sit at .63V at idle no matter the conditions. Something is messed up there. The TPS itself could be malfunctioning when it gets warmed up (I assume you swapped your 4 pin TPS onto your 1g TB?).

The only other *possible* cause would be a voltage spike across the reference wire only when it gets warmed up. Which would be rather unlikely. Your idle problem, I'd put money on, lies within whatever is causing the TPSvolts to increase, however, your fuel trims need to be fixed as well.

Gotcha - I'll start focusing on that. If you look back at one of my replies you'll notice that I found the O2 voltage sticking when the revs are stuck at the higher levels when the car was running hot. Could the TPS voltage being higher simply be a result of a bad O2 sensor getting stuck and telling the system it needs more air? The reason I'm not thinking it's the throttle body is because I just put this rebuilt on in (and yes, I swapped in the 2g TPS) and it's still having issues. I'm really thinking it's the TPS, the O2, or maybe something odd like a failed FPR diaphragm. I've checked the slack on the throttle cable a couple times now. It is directly related to engine temps - once they go above normal operating temps (over 200) the idle climbs and sticks. That's why the first thing I changed was the coolant temp sensor.

 

[1LE]

It is directly related to engine temps - once they go above normal operating temps (over 200) the idle climbs and sticks. That's why the first thing I changed was the coolant temp sensor.

That's the really weird part to me. By default (unless you overrode it), the ECU will start pulling idle timing slightly when over optimal temperature. That causes a *decrease* in idle speed if the ISC isn't there to compensate...

 

[Ludachris]

That's the really weird part to me. By default (unless you overrode it), the ECU will start pulling idle timing slightly when over optimal temperature. That causes a *decrease* in idle speed if the ISC isn't there to compensate...

I've tried not to change much in Link since I had English Racing tune it back in November, but that was on a different turbo so I know the tuning needs adjusting. I just don't think it should be so far off at idle though. Something's wrong, just wish I could track it down... ugh.

 

[Tyeler18]

Gotcha - I'll start focusing on that. If you look back at one of my replies you'll notice that I found the O2 voltage sticking when the revs are stuck at the higher levels when the car was running hot. Could the TPS voltage being higher simply be a result of a bad O2 sensor getting stuck and telling the system it needs more air? The reason I'm not thinking it's the throttle body is because I just put this rebuilt on in (and yes, I swapped in the 2g TPS) and it's still having issues. I'm really thinking it's the TPS, the O2, or maybe something odd like a failed FPR diaphragm. I've checked the slack on the throttle cable a couple times now. It is directly related to engine temps - once they go above normal operating temps (over 200) the idle climbs and sticks. That's why the first thing I changed was the coolant temp sensor.

The o2 sticking could be due to the car just constantly running rich. It's not cycling back to lean because it physically can't, it could infact be reading correctly and you're just running that rich.

Now as far as the TPS- The computer has zero control over TPS volts. TPS signal is an input. All the computer does is send it 5v as a reference, that is the only thing the ECU "controls" over it. From there the built in potentiometer controls how much voltage is sent back to the computer. As the throttle plate turns there's a blade inside the TPS that moves across that potentiometer and changes the resistance. That change in resistance is what changes the voltage traveling to the computer to let it know how far open the throttle plate is. Understand?

There's only really 2 possibilities to your TPSvolts increasing and that's a defective sensor (I'd assume this is your problem) or the throttle plate sticking once warmed up (harder to believe is occurring to both TB's you've tried). Heat does terrible things to electronics, and it's not that uncommon for something like this to happen. The only way to truly determine if the sensor is at fault though is to log TPSvolts and then when you see it jump back up to .73V at idle, try and turn the throttle plate closed by hand. If it goes all the way back down to .63V you're plate is sticking, if it doesn't then the sensor is defective.

Just remember that the computer has no control over what the TPS does. It sends 5V to it no matter what, from there you're foot controls how much voltage is sent back to the computer, that's all there really is to it.

 

[1LE]

Say, how does/did y'alls DSMs act when stock(ish) in regards to idling at high temps/with accessories on?

Now that it's in the 90's and dark enough to use headlights again, I'm getting some more test points...

- With headlights on, it tends to drop to 700rpms at lights, then creep up to 750.
- With high underhood temps (enough to activate fans and start retarding the timing) it will sometimes idle as low as 680rpms.
- Under test conditions, but with this warmer air when revved it drops to about 725rpms (seemed like it was doing 740ish on the cooler days we had), then creeps up to 750.

I still don't have any way to measure the ISC position, but wonder if perhaps the BISS is a smidge too tight, giving me a natural idle of something less than 750? Either way, it'd be within the 750 +/-50 test condition spec in the manual.

My reason to NOT touch it is that when it gets down to -15 degrees here I don't want my idle to be too high with the much denser air. It has to stay controllable by the ISC to avoid a MIL. I don't have a way to disable that MIL condition and I don't like it when it's on as I then won't notice if I have another issue crop up.

My reason TO touch it is concerns over how low the idle can safely go and still supply sufficient oil pressure. Way back in the day when I first got it, I adjusted the BISS to idle per the tach to 750 (not realizing the stock tach was off by over 100 rpms at the bottom end and actually idling at less than 650 rpms normally). I was getting an occasional flicker from the oil pressure light under the hot underhood temperature/fans running condition (best guess is that it was probably idling at around 525-550, never measured it though as I didn't have accurate data at that time). Now I have accurate RPMs (so I can verify I'm not down that low) and I also have an upgraded high volume oil pump, but want to make sure I'm safely above minimum oil pressure... Side note, the manual states that 650 rpms is normal for "new engines" when adjusting the BISS, whatever that means, so I'd hope that even as low as 600rpms would have enough oil pressure?

 

[Ludachris]

I think I have mine finally figured out... but don't want to say anything just yet. Parts are on order. Fingers are crossed.

 

[Ludachris]

It was the cruise control cable, figures. Swapped in a non-cruise cable and the idle is now fine. Now everyone knows - if there's a direct correlation with high temps when the idle gets stuck running higher, ask if they have cruise control.

 

[1LE]

It was the cruise control cable, figures. Swapped in a non-cruise cable and the idle is now fine. Now everyone knows - if warm temps are involved with the idle issues, ask if they have cruise control.

Good to know. I have a friend that has an increasing idle as the car warms up. I took a look at it one time and noted that the throttle would not snap closed as the car got warm. It's definitely being held open somewhere, kind of "mushes" as it closes and won't hit the stop. I'll tell him to check the cruise cable.

 

[Ludachris]

Good to know. I have a friend that has an increasing idle as the car warms up. I took a look at it one time and noted that the throttle would not snap closed as the car got warm. It's definitely being held open somewhere, kind of "mushes" as it closes and won't hit the stop. I'll tell him to check the cruise cable.

Bet that's the issue. I noticed that when the idle was high, I'd park, pop the hood and was able to close the throttle plate by hand and the idle dropped. This was after adjusting the slack in the cable a couple times before that. F'ing cruise control. Oh well, at least it's finally fixed. If there's an actuator in there then I guess that could make sense it moving with high temps and not low temps.

Now I have to reinstall the FIAV and TPS so that I don't have to manually keep the car running in the mornings for the first few seconds after starting it.

 

[911gdsmboostin]

are the cruse control cables and non cruse control throttle cables different?? I am (out of nowhere ) having this excat issue.. all though I have had the issue when I start a cold start is idle surges up to 1500-2000 back down to normal idle for about a min or 2 until some heat gets into motor then it calms down and always idleds around 1000 or just a little under and now for some reason when it gets warm it wants to idle at 2000-2300 I pulled clost the throttle butterfly and it helped it down to about 1300-1500 and I couldn't see if it was closed 100% or what but it was tight pulling back.. could the cable be not letting it back al the way??