Can you help me diagnose problem via FORScan w/ Laptop?

[SyberTiger]

Okay....the high idle problem came back today and instead of resetting the PCM (battery disconnect) I went ahead and hooked up FORScan to see if I could find the problem. I only went on a 3 mile trip to the post office and halfway there at a stop light I noted the idle was now around 1,700 RPM. Click HERE to see the FORScan graph from 9 days ago after I had reset the PCM and everything seemed to run/idle fine. Now click HERE to see the FORScan graph taken today with the high idle problem active. You'll see in there that I punched up the RPM at one point to around 3,000 RPM.

The differences I see today are several: The TP MODE is always at PT (part throttle) whereas in the first graph the mode is CT (closed throttle) when idling then PT when I push the accelerator. So the question is, what causes PT when I'm not pushing the accelerator. Is the cause the throttle position sensor or a vacuum leak? Also I note that long term fuel trim bank 1 is always sitting around +3.9 regardless of the RPM. Lastly, the IAC is commanded to be 68% the entire time regardless of idling or punching up the RPM.

 

[2000StreetRod]

In the earlier graph the TPS voltage minimum was 0.90 volts. Since that was immediately after clearing keep alive memory (KAM) the PCM assumed that value to be closed throttle. In the later graph the TPS minimum voltage is 0.91 volts which is greater than the KAM closed throttle voltage so it is declared part throttle. The difference in voltage (1%) is not enough to significantly affect the idle speed. Since the throttle plate is not open (based on the TPS voltage) then air is bypassing the throttle allowing higher engine speed. The air flow could be due to the IAC valve or a vacuum leak. If the source is the IAC valve then the MAF sensor will detect the increased air flow and the PCM adjusts the fuel accordingly. If the source is a vacuum leak then the MAF sensor won't detect the increased air flow and the fuel mixture will be lean. I suspect there is a vacuum leak in bank 1 (passenger side) because LTFT is +3.91 now and was about +1 in the earlier graph. You could confirm the source by recording the MAF counts at normal idle and high idle. Make sure the engine load is the same: drive or park and A/C on or off. In my opinion, the only reliable method of detecting a vacuum leak is with a smoke machine.

 

[lincolnshibuya]

doesn't look like a vacuum leak IMO.. could be an issue with the IAC and/or MAF. Vacuum leaks tends to make the STFT very high on idle and go down to 0 when at high rpm (you only need vacuum on idle)

have you tried disconnecting the MAF when it's high idling?

also try check if you can do an active test on IAC, if whatever percent you commanded doesn't reflect on how it idles then your IAC is defective..

 

[SyberTiger]

Until I get the idle back to "normal" I can't go back and compare and contrasts the MAF counts so I'll hold off on that and not reset the PCM/KAM, etc.

However, to see the impact of disconnecting the MAF and the IAC click HERE. I denoted the period the MAF was unplugged then the IAC unplugged. Unplugging the MAF had not make a discernable impact on the idle speed. Unplugging the IAC did by dropping the idle from around 1,800 down to 740 RPM. I note the PCM really didn't care about the unplugged IAC with regard to commanded percentage. I seem to recall that with the IAC unplugged the engine should stall or struggle maintaining a minimum idle RPM but that didn't happen. So, what's keeping the engine idling at 740 when the IAC is unplugged? Could it be the IAC is stuck open?

I'm fairly new with FORScan so I haven't delved into how to change the IAC commanded value. Can you provide some data on that?

 

[2000StreetRod]

When the MAF sensor is disconnected the PCM relies on the TPS voltage to estimate air flow.

On my Sport I adjusted the throttle stop so the engine speed is less than normal but not low enough for the engine to stall. That way I can detect when the IAC valve has failed but still drive the vehicle. You may be recording the wrong PID for commanded idle speed. In my tune there are multiple commanded idle speeds: vehicle not moving in park/neutral vs drive; A/C on or off, vehicle moving with closed throttle. Have you seen any change in commanded for any of the previous configurations?

If your IAC valve were stuck open the engine speed would be well above 740. If it were stuck closed your engine speed would not reach 1,800 rpm at closed throttle. I suspect your IAC valve is defective and not responding correctly to PCM commands. I had to replace the one on my 2003 V8 recently because the engine was stalling. I tested it with a battery charger and it sounded like a buzzer.

 

[SyberTiger]

I don't know that there's another PID for idle speed so I'll have to take another look next time I have FORScan setup. All my graph are with the vehicle sitting in the garage at "no throttle". It makes sense to me that there would be other commanded "idle" targets for various scenarios. I always wondered why, when I let go of the accelerator the engine RPM doesn't drop down to 672 or something close. I thought that maybe forced air from the vehicle coasting may be the reason why the engine doesn't drop down. I'm sure a little air still gets past the throttle plate when coasting....it isn't "air tight".

It would seem to me that the very first graph I shared (THIS one where the idle was correct after a PCM/KAM reset). From the graph we can see the PCM wants the idle to be high-ish when cold but as the engine warms up the commanded idle speed goes down until it settles at 672 RPM. I would think the commanded idle speed should stay the same (at 672) regardless of the engine load at idle (in Park or Drive at a full stop) and it would be up to the PCM to control the engine such that it tries to stay at the targeted warm-engine idle speed of 672. No?

In the latest graph, during the time the IAC was unplugged, the commanded idle RPM was about 740 and the actual RPM was around 740. Strange coincidence? It kind of sounds like the IAC may be stuck open a bit more than it should. I seem to recall that fully closed the IAC percentage is supposed to be around 20%. I note that with the "good scenario" graph with normal idle speed the commanded IAC is eventually set to around 38% which seems reasonable given that the engine has reached normal operating temperature and the target RPM is sitting at 672. In that scenario, as I recall, if the IAC is unplugged the engine should stall out since this would emulate a 20% or "full-closed" on the IAC valve.

 

[SyberTiger]

I happen to have a few old Motorcraft IACs laying about....long story. I changed out the IAC with a Motorcraft IAC I had bought a few years ago. It "should" be a good one but I don't know for sure as at the time I was chasing another idle issue and bought an extra because I thought it might be defective from the factory.

Anyhow, HERE are my latest results. I don't note anything significant to report as the engine seems to be operating in the same fashion as with the prior IAC. For grins I including the DASHBOARD SNAPSHOT at the end of the graphing and the FORScan LOG that shows the PCM DTC codes set because of unplugging the MAF and the IAC.

From the very first graph I shared when the engine was idling properly I note the IAC percentage is around 40%. But in all the subsequent graphs when the engine is idling very high the IAC is aways 65 - 70%. Three questions:

1. Why is the PCM commanding the PCM to be 66 - 70% when it appears closer to 30% is correct?
2. Why is it when I disconnect the IAC the engine RPM drops from 1600+ RPM down to 740 but does not drop down even further which is typical for Explorers to stall when you do that?
3. Should I have reset the PCM/KAM after changing out the IAC?

 

[lincolnshibuya]

Until I get the idle back to "normal" I can't go back and compare and contrasts the MAF counts so I'll hold off on that and not reset the PCM/KAM, etc.

However, to see the impact of disconnecting the MAF and the IAC click HERE. I denoted the period the MAF was unplugged then the IAC unplugged. Unplugging the MAF had not make a discernable impact on the idle speed. Unplugging the IAC did by dropping the idle from around 1,800 down to 740 RPM. I note the PCM really didn't care about the unplugged IAC with regard to commanded percentage. I seem to recall that with the IAC unplugged the engine should stall or struggle maintaining a minimum idle RPM but that didn't happen. So, what's keeping the engine idling at 740 when the IAC is unplugged? Could it be the IAC is stuck open?

I'm fairly new with FORScan so I haven't delved into how to change the IAC commanded value. Can you provide some data on that?

FORScan forum • View topic - EATC climate control active test - problem

if you click on the IAC Quick Test it will show you options for testing.

I think the OTM (output test mode) has lots of useful goodies too to play with..

 

[SyberTiger]

I think my problem is that I can't seem to find or figure out how to do an IAC test.

Click THIS.

I'm not so sure it's an IAC issue...seems more like a problem with the PCM telling the IAC to open up the valve to 65 - 70% whereas it should be more like 30% from what I can tell. Why is the PCM commanding 65%?

 

[SyberTiger]

There is no IAC test available on my FORScan as I previously showed. Anyway, I've come to the conclusion that the problem is not the IAC. The fast idle is causes by the PCM commanding the IAC to open up. I don't have a clue as to why the PCM wants to open up the IAC but I can see that the throttle position mode is set to PT (part throttle) when it should be CT (closed throttle) even though the throttle position sensor voltage is 0.90 - 0.91.

Because I can't seem to get anywhere with this I went ahead and reset the PCM/KAM. Basically, just unhook the positive battery terminal then run a jumper from unconnected positive battery cable to the negative battery terminal, flip on the headlights and turn the key to the start engine position. Then, with the PCM/KAM reset the engine idles just fine. Click HERE to see how then engine should be operating after PCM reset. Note that the IAC is commanded to be 28.8% and the TPS is set to CT. Contrast this with THIS pre-reset-PCM graph when I have the high idle problem and note that the IAC is commanded to be 65+% and the TPS is set to PT. The only other difference I see with the fast-idle graph is the LTFT, particularly bank 1, seems to be riding a bit higher for the duration of the graph (3.25% vs 0.39% for good-idle graph).

When the fast-idle problem shows up again, is there anything in FORScan that can help tell me why the PCM is command to be 65% open or why the TPS is mode is PT even though the TPS voltage is only 0.91? 65% IAC is a pretty hefty number and at the same time the PCM is commanding a 672 RPM.

Read my next post and specifically the last paragraph from the Ford manual excerpt posted. Perhaps the problem I'm seeing can be explained by corrupt "ratch" stored in the KAM. How do I read out the ratch number stored in the KAM?

 

[SyberTiger]

For the benefit of anyone reading this thread and because I use this forum so that I can refer back to issues I dealt with I'm including the following excerpts from the Ford Service Manual on IAC and fuel trim:

------------------------------------------
Fuel Trim

Short Term Fuel Trim
If the oxygen sensors are warmed up and the PCM determines that the engine can operate near stoichiometric air/fuel ratio (14.7:1 for gasoline), the PCM enters closed loop fuel control mode. Since an oxygen sensor can only indicate rich or lean, the fuel control strategy continuously adjusts the desired air/fuel ratio between rich and lean causing the oxygen sensor to switch around the stoichiometric point. If the time between rich and lean switches are the same, then the system is actually operating at stoichiometric. The desired air/fuel control parameter is called short term fuel trim (SHRTFT1 and 2) where stoichiometric is represented by 0%. Richer (more fuel) is represented by a positive number and leaner (less
fuel) is represented by a negative number. Normal operating range for short term fuel trim is +/- 25%. Some calibrations have time between switches and short term fuel trim excursions that are not equal. These unequal excursions are used to run the system slightly lean or rich of stoichiometric. This practice is referred to as using bias. For example, the fuel system can be biased slightly rich during closed loop fuel to help
reduce oxides of nitrogen (NO x ).

Values for SHRTFT1 and 2 may change significantly on a scan tool as the engine is operated at different RPM and load points. This is because SHRTFT1 and 2 react to fuel delivery variability that changes as a function of engine RPM and load. Short term fuel trim values are not retained after the engine is turned off.

Long Term Fuel Trim
While the engine is operating in closed loop fuel control, the short term fuel trim corrections are learned by the PCM as long term fuel trim (LONGFT1 and 2) corrections. These corrections are stored in the keep alive memory (KAM) fuel trim tables. Fuel trim tables are based on engine speed and load and by bank for engines with 2 heated oxygen sensor (HO2S) forward of the catalyst. Learning the corrections in KAM improves both open loop and closed loop air/fuel ratio control. Advantages include:

• Short term fuel trim does not have to generate new corrections each time the engine goes into closed loop.
• Long term fuel trim corrections can be used both while in open loop and closed loop modes.

Long term fuel trim is represented as a percentage, similar to the short term fuel trim, however it is not a single parameter. A separate long term fuel trim value is used for each RPM/load point of engine operation. Long term fuel trim corrections may change depending on the operating conditions of the engine (RPM and load), ambient air temperature, and fuel quality (% alcohol, oxygenates). When viewing the LONGFT1/2 PID(s), the values may change a great deal as the engine is operated at different RPM and load points. The LONGFT1/2 PID(s) display the long term fuel trim correction that is currently being used at that RPM/load point.

Idle Air Trim

Idle air trim is designed to adjust the idle air control (IAC) calibration to correct for wear and aging of components. When the engine conditions meet the learning requirement, the strategy monitors the engine and determines the values required for ideal idle calibration. The idle air trim values are stored in a table for reference. This table is used by the PCM as a correction factor when controlling the idle speed. The table is stored in the KAM and retains the learned values even after the engine is shut off. A DTC is set if the idle air trim has reached its learning limits.

Whenever an IAC component is replaced, or a repair affecting idle is carried out, it is recommended that the KAM be reset. This is necessary so the idle strategy does not use the previously learned idle air trim values.

To reset the KAM, refer to Section 2, Resetting The Keep Alive Memory (KAM) . It is important to note that erasing DTCs with a scan tool does not reset the idle air trim table.

Once the KAM has been reset, the engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim values. Idle quality improves as the strategy adapts. Adaptation occurs in 4 separate modes as shown in the following table.

IDLE AIR TRIM LEARNING MODES

1. NEUTRAL A/C ON
2. NEUTRAL A/C OFF
3. DRIVE A/C ON
4. DRIVE A/C OFF

Idle Speed Control Closed Throttle Determination — Applications Without Electronic Throttle Control

One of the fundamental criteria for entering RPM control is an indication of closed throttle. Throttle mode is always calculated to the lowest learned throttle position (TP) voltage seen since engine start. This lowest learned value is called ratch, since the software acts like a one-way ratch. The ratch value (voltage) is displayed as the TPREL PID. The ratch value is relearned after every engine start. Ratch learns the lowest, steady TP voltage seen after the engine starts. In some cases, ratch can learn higher values of TP. The time to learn the higher values is significantly longer than the time to learn the lower values. The brakes must also be applied to learn the higher values.

All PCM functions are done using this ratch voltage, including idle speed control. The PCM goes into closed throttle mode when the TP voltage is at the ratch (TPREL PID) value. An increase in TP voltage, normally less than 0.05 volts, puts the PCM in part throttle mode. Throttle mode can be viewed by looking at the TP MODE PID. With the throttle closed, the PID must read C/T (closed throttle). Slightly corrupt values of ratch can prevent the PCM from entering closed throttle mode. An incorrect part throttle indication at idle prevents entry into closed throttle RPM control, and could result in a high idle. Ratch can be corrupted by a throttle position sensor or a circuit that drops out or is noisy, or by loose/worn throttle plates that close tight during a deceleration and spring back at a normal engine vacuum.
------------------------------------------

 

[lincolnshibuya]

There is no IAC test available on my FORScan as I previously showed. Anyway, I've come to the conclusion that the problem is not the IAC. The fast idle is causes by the PCM commanding the IAC to open up. I don't have a clue as to why the PCM wants to open up the IAC but I can see that the throttle position mode is set to PT (part throttle) when it should be CT (closed throttle) even though the throttle position sensor voltage is 0.90 - 0.91.

Because I can't seem to get anywhere with this I went ahead and reset the PCM/KAM. Basically, just unhook the positive battery terminal then run a jumper from unconnected positive battery cable to the negative battery terminal, flip on the headlights and turn the key to the start engine position. Then, with the PCM/KAM reset the engine idles just fine. Click HERE to see how then engine should be operating after PCM reset. Note that the IAC is commanded to be 28.8% and the TPS is set to CT. Contrast this with THIS pre-reset-PCM graph when I have the high idle problem and note that the IAC is commanded to be 65+% and the TPS is set to PT. The only other difference I see with the fast-idle graph is the LTFT, particularly bank 1, seems to be riding a bit higher for the duration of the graph (3.25% vs 0.39% for good-idle graph).

When the fast-idle problem shows up again, is there anything in FORScan that can help tell me why the PCM is command to be 65% open or why the TPS is mode is PT even though the TPS voltage is only 0.91? 65% IAC is a pretty hefty number and at the same time the PCM is commanding a 672 RPM.

Read my next post and specifically the last paragraph from the Ford manual excerpt posted. Perhaps the problem I'm seeing can be explained by corrupt "ratch" stored in the KAM. How do I read out the ratch number stored in the KAM?

I'll try running my Forscan this weekend to check out where that test is, it should be warm enough to do the test outside the garage. It's been a long time since I have used it for my mountaineer, it's been the navigator everytime I used it.

 

[SyberTiger]

I'll try running my Forscan this weekend to check out where that test is, it should be warm enough to do the test outside the garage. It's been a long time since I have used it for my mountaineer, it's been the navigator everytime I used it.

Thanks, and let me know if you can figure out how to get a readout of the ratch value out of the KAM.

 

[SyberTiger]

Other reference links for those looking into IAC and Fuel Trim issues:

Fuel trim can be a valuable diagnostic tool​

How to trouble shoot IAC idle problems​

 

[lincolnshibuya]

Thanks, and let me know if you can figure out how to get a readout of the ratch value out of the KAM.

on the Oscilloscope section when you hit the PIDs (gear icon) select the Control PIDs instead of Read, it will show you the options to control.. It started to rain so I have to wrap it up.. didn't find the ratch value yet on Forscan.

 

[SyberTiger]

Ah, CONTROL....I didn't notice that before. A big THANK YOU for taking the time to post the video. Please let me know if you come across the ratch value some time later. The more and more I think about it, corrupted a ratch value would explain a lot as to why I get into that occasional high idle problem. I'll have to check my records but I thought I had replaced the TPS a long time ago back when I just started switching out parts because I could not figure this problem out.

 

[SyberTiger]

I went back out and took another look. I believe TPCT (throttle position closed throttle) is the ratch value as seen HERE. I'll have to wait for the fast idle problem to show up again and then look at this value. My theory would be that instead of having a 0.90 value it'll be something less like 0.80 for example.

Using 0.80 as an example, the PCM would see the difference of 0.80 and the 0.90 /0.91 value of the TP_V voltage and conclude that the throttle has been opened up, ergo PT (part throttle). Then, the PCM would increase the IAC % to a corresponding value and the result would be a fast idle.

 

[SyberTiger]

Well, 7 weeks later and the fast idle hasn't come back. Just kind of weird it showed up and went away without be doing anything other than to clear the computer and force it to re-train.

 

[edcantu9]

Before I changed out the intake manifold the high idle problem would usually show up after a week, or two, or four and generally the high idle problem might start out at 800 RPM, then eventually creep up to 1,500 or more over a period of several local drives...and, the high idle problem was usually evident after the vehicle was warmed up and I would be sitting at a stop light.

However, after I replaced the intake manifold about 14 month ago I held my breath and waited several weeks and declared the problem was resolved...and every month that went by I was convinced the problem was solved. But, after 14 months it showed up again and then instead of by usual ritual of cleaning the IAC and throttle body plus disconnect the battery I decided to only disconnect the battery. The graph you see if after the battery disconnect and the apparent KAM being cleared. Now it's running just fine. I suppose I'll have to wait until the problem shows up again then run FORScan with all the PIDs to see if I can figure out what's wrong. For now though I was hoping you all could give me a clue as to what the likely problem could be so I can fix it without waiting for the problem to show up again. But, it sounds like, so far, everything looks good.

You don't have to disconnect the battery. There is an option is Forscan to clear KAM.

 

[SyberTiger]

Old thread but 4 years later I still occasionally see the high idle issue. Resetting the KAM always makes the problem go away until it randomly shows up again. I'm coming to the conclusion that the "circuit drops out" on occasion and causes the ratch to become corrupted. Was just reading up on ratch determination from ALLDATA which reads as:

Idle Speed Control Closed Throttle Determination
One of the fundamental criteria for entering rpm control is an indication of closed throttle. Throttle mode is always calculated to the lowest learned throttle position (TP) voltage seen since engine start. This lowest learned value is called "ratch," since the software acts like a one-way ratch. The ratch value (voltage) is displayed as the TPREL PID. The ratch value is relearned after every engine start. Ratch will learn the lowest, steady TP voltage seen after the engine starts. In some cases, ratch can learn higher values of TP. The time to learn the higher values is significantly longer than the time to learn the lower values. The brakes must also be applied to learn the longer values. All PCM functions are done using this ratch voltage, including idle speed control. The PCM goes into closed throttle mode when the TP voltage is at the ratch (TPREL PID) value. Increase in TP voltage, normally less than 0.05 volts, will put the PCM in part throttle mode. Throttle mode can be viewed by looking at the TP MODE PID. With the throttle closed, the PID must read C/T (closed throttle). Slightly corrupt values of ratch can prevent the PCM from entering closed throttle mode. An incorrect part throttle indication at idle will prevent entry into closed throttle rpm control, and could result in a high idle. Ratch can be corrupted by a throttle position sensor or circuit that "drops out" or is noisy, or by loose/worn throttle plates that close tight during a decel and spring back at a normal engine vacuum.