High Idle. Lanos 1.6 DOHC

[tirbuson]

Hello,

I would like to thank in advance whoever spends his/her time reading and maybe responding to my post.

Let me first give you a brief historical background to my problem. I initially got a crankshaft position sensor (CPS) error which I resolved with a new sensor. However, just after the replacement I started to have the problem of high idling (>2000 rpm.). Thinking it cannot be coincidence that the high idling started just after the replacement of CPS, I suspected that I bought a peculiarly malfunctioning CPS. I bought another one but the high rpm situation did not differ.

Then, I thought, while replacing the CPS, perhaps I accidentally disconnected or damaged the cable controlling the idle air control valve (IACV.) In order to test that I unscrewed the IACV, turn the ignition on and off without starting the engine to see whether IACV's pintle moved. It did. (However, it turned out this was not a smart way of doing it. Later when I was illustrating the method to a friend with an old IACV, the pintle at the tip of the spring became a projectile. Luckily it did not hit any of us in the eye.) Anyway, since the IACV looked little dirty, I cleaned it together with its socket using throttle body spray. Idling was okay (~850 rpm) for 2 days, but then it started to rev above 2000 rpm. This gave me the false hope that the IACV was at the end of its life, cleaning it helped for 2 days and replacing it would be the solution. I replaced it, did the idle learning cycle etc., but the problem persisted.

Later, I thought may be the Throttle Position Sensor (TPS) is the problem. Found it cheap at the local store. Replaced it, but it did not help.

Next step was to detect not so obvious vacuum leaks. Visually everything looks okay and I am not keen on performing the dangerous propane or carburetor spray test. Instead, I wanted to drive around with my laptop logging obdII data to see whether there is any indication of a vacuum leak in the first place. Here is what I have found:
With the ignition ON
Intake Air Pressure 29.8 (which is close to the barometer reading of 30.02)
------------------------------------------------------------------------------------------------
Just after the idle learning and driving a mile things are looking good.
Speed: 0
RPM: 847
Throttle Pos %: 0.0
Engine Load %: 4.7
Coolant Temp: 176
Timing Advance Deg: 11.5
Intake Pressure: 11.8
Intake Air Temp: 95
Short Term Trim %: 0.0
Long Term Trim %: -6.3
-------------------------------------------------------------------------------------------------
After 5 minutes of driving on the highway, high rpm comes back at idling
Speed: 0
RPM: 1751
Throttle Pos %: 2.4
Engine Load %: 5.9
Coolant Temp: 190
Timing Advance Deg: 27.5
Intake Pressure: 7.4
Intake Air Temp: 64
Short Term Trim %: 5.5
Long Term Trim %: -18.0

There are two things I noticed. First, while idling, throttle position is not zero anymore. Second, the long term trim is very high and negative. If there was a vacuum leak, shouldn't it be the case that long term trim is set to be positive to make the mix richer?

During cruising, intake pressure drops as the car decelerates and increases as it accelerates. So metered or unmetered the pressure seems to be okay. There is no leak. Am I right? If so, why is LT Trim is this high and negative. And why is the throttle not fully close at idling.
-------------------------------------------------------------------------------------------------------------
Later, while cold idling I got even more throttle opening
Speed: 0
RPM: 2035
Throttle Pos %: 7.1
Engine Load %: 9.0
Coolant Temp: 100
Timing Advance Deg: 32.5
Intake Pressure: 8.3
Intake Air Temp: 72
Short Term Trim %: -14.1
Long Term Trim %: -6.3

Now the throttle position is idling at 7.1%. I do not understand why? TPS is new.
By the way, is it normal that the engine got into the closed loop at 100F?

Does anybody have any idea why I am having a high idle? Also, is idle speed somehow connected to crankshaft position sensor?

Thank you very much.

[jidasas]

How are the wires to your tps sensor? I had a similar problem and my solution involved finding a break in the wires for the tps...the wire looked intact but was broken inside.

[tirbuson]

Thank you for your interest in replying.

The way I test for that is through OBDII. While the ignition is on but the car is not running, if I control the throttle position manually, this is reflected by the OBDII reading proportionally. Therefore, I conclude that the ECU is aware of the throttle behavior.

I recently realized that when I try to fill up the car at a gas station, the fuel pump at the station automatically disengages even though the tank is almost empty. I think there is a pressure issue in the EVAP system. I am suspecting and wishfully thinking that the Canister Purge Solenoid has a hand in the whole thing. Strangely, Daewoo, (if I am not mistaken) names the unit as PCV (I guess it stands for Purge Canister Valve or Pressure Canister Valve. If not, I would like to know.) I think its part number is 1997210. This unit is connected to the intake manifold and, if I am not mistaken again, releases fuel vapor into the manifold. I am currently reading more about the basics before I form a theory to act upon:

* First, I am trying to understand whether it is possible for the Canister Purge Solenoid to cause a high idle and a very negative fuel trim by erratically introducing fuel vapor.

* Second, I am wondering whether the problem I experienced filling up the tank is related to the Canister Purge Solenoid or something else in the EVAP system. (By the way, I experienced the same problem at different gas stations.)

* Third, I am reading to learn a method to safely test the Canister Purge Solenoid and, later, more broadly the EVAP system.

I might have raised an illogical and impossible theory. If so, it is because I am in the process of learning. I welcome other suggestions to solve the high idle problem, centered, or not, on the EVAP system.

Thank you very much for your attention.

[tirbuson]

Well, it turned out that the reason why I could not pump any gas is that the vent-valve-side of the Canister was clogged. I replaced the Canister. Now I can pump gas again. How on earth the car was passing the asynchronous self EVAP test with a clogged canister is beyond me.

High idle saga continues. I also got suspicious of the ECU, found a replacement under 50$ but that did not solve the problem. Checked every wiring from the related sensors to the ECU with a multimeter, they were all okay.

I am almost sure that there is no structural problem. My friend has this scan tool from obd-2.com with which we can control the idle air valve. While the car is idling when we extend the valve it kills the engine. Therefore, it guarantees that there is no leak. Also if there was a structural leak the rpm would not be temporarily normal after the ecu reset and the idle training. The idle RPM sometimes shoots up to 3000.

Now, I also have a p0172 with a healthy oxygen sensor. Ecu decided to inform me that it is running rich. I have been aware of it for a long time (notice the previous posts). High idle while running rich with a healthy oxygen sensor is like being cold in a desert. Very puzzling behavior. I think the ECU does not like one parameter and starts chasing it for corrections with its limited sophistication, hopelessly defaults to this weird behavior.

Then, I read on the internet that after replacing the crankshaft position sensor, one should perform the crankshaft variation training. (To remind you, everything started just after I replaced the Crankshaft sensor. Being a genius I lost the old sensor so I am not able to test this idea by putting it back and checking the idle) I do not have the necessary tools to do the variation training. i.e. Scan-100 or Tech2. The mechanics who I called are treating me as if I am from the planet Mars. If there is any other Martian around here, I like to listen your two celestial cents.

Thanks.

[tirbuson]

Finally, the ECU threw the long awaited P1336 (Crankshaft Variation Relearn).

Although my ECU is an obtuse one, it is still functioning. The funny but understandable thing is that after the code, the high idle and the rich mixture conditions are gone. The car is running smoothly.

Now I have to find a mechanic with a Tech2 or a Scan-100 tool.

[Daniel]

Finally, the ECU threw the long awaited P1336 (Crankshaft Variation Relearn).

Although my ECU is an obtuse one, it is still functioning. The funny but understandable thing is that after the code, the high idle and the rich mixture conditions are gone. The car is running smoothly.

Now I have to find a mechanic with a Tech2 or a Scan-100 tool.

Thanks for sharing. I didn't knew that crankshaft sensor replacement can lead to high idling and should be followed by such procedure.

BTW did you tried a ECU update?

[tirbuson]

Hi Daniel,

No, I did not try an ECU update because I do not know how. I think writing anything to a Daewoo ECU requires a Scan-100 or a Tech2 tool. If you know any other method I may also use it to get my ECU to relearn crank variation.

I tried a different ECU with no effect though. However, later I learned that it would not make a difference in my case because replacing ECUs also requires crank relearn.

[Doely]

I myself am new to daewoos and "sensor technology", but if your car has given the code but now responds well, would it be worth doing a ECU reset then the IACV relearn procedure? Sounds like you're not far from fixing this though. I'm having similar (not as severe) issues with my wifes Tacuma, I suspect an 02 sensor or TPS now, but like you i'll keep chipping away...

[tirbuson]

The GM dealer does not want to fix the car. Independent mechanics don't have the necessary scan tools. Three of them gave me hope initially but at the end their tools does not perform the relearn.

Now I am coming up with my own make-shift relearn procedure. My friend have this software that is supposed to perform the CASE relearn on N-type 4 injection GM cars. I tried the procedure with it unsuccessfully. I guess it is not completing the relearn. The high idle symptoms came back.

I will keep trying next couple weeks and let you know about the results.

[tirbuson]

I myself am new to daewoos and "sensor technology", but if your car has given the code but now responds well, would it be worth doing a ECU reset then the IACV relearn procedure? Sounds like you're not far from fixing this though. I'm having similar (not as severe) issues with my wifes Tacuma, I suspect an 02 sensor or TPS now, but like you i'll keep chipping away...

P1336 is a hard code, I cannot clear it with a scan tool for example. But I would not clear it anyway. Without the code, mechanics were not convinced that the car needs a crank relearn.

[Topher39]

So how did it end?