I've officially found the most unsolvable idle issue...

[Ecomike]

Alright, so I replaced a few couplers on my "custom" air intake, and replaced the throttle body gasket. The jet engine sound is gone and my idle is steady, but it's idling sorta high now. About 1000. However, it still struggles to return to idle after getting on the gas. I think I've narrowed it down to bad circuitry in the IAC. Or just a bad IAC (yes, I cleaned it and the throttle body) Does anyone have reference ohm and voltages to the IAC?

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That may be normal, mine idles at about 1200 rpm until I am nearly totally stopped (maybe 5 mph?) when slowing down from say 60 mph on a freeway off ramp to a stop light. I have almost never had a high idle problem caused by the IAC. It has always been vacuum leaks including the MAP sensor vacuum line at the throttle body, leaking fuel pressure regulators dumping fuel into the intake manifold, bad grounds to the TPS and bad IAT temp sensors in the intake manifold.

The IAC is digital, never seen any test voltages published, and the complete Noid light test kits on Ebay have a noid light tester for the Jeep IAC!!!!

 

[Ecomike]

Alright, so I replaced a few couplers on my "custom" air intake, and replaced the throttle body gasket. The jet engine sound is gone and my idle is steady, but it's idling sorta high now. About 1000. However, it still struggles to return to idle after getting on the gas. I think I've narrowed it down to bad circuitry in the IAC. Or just a bad IAC (yes, I cleaned it and the throttle body) Does anyone have reference ohm and voltages to the IAC?

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The IAC is basically a TPS style sensor guts wise Is my best guess, and the ohms varies with the position of the motor, and the motor is a step motor that operates in two directions in pulse step signals from the ECU, pulse steps like the fuel injectors. No an EE, so that is best I can explain it.

A noid light will signal if the wiring/ECU is sending signals to open or close the port size.

 

[W1zardofozz]

That may be normal, mine idles at about 1200 rpm until I am nearly totally stopped (maybe 5 mph?) when slowing down from say 60 mph on a freeway off ramp to a stop light. I have almost never had a high idle problem caused by the IAC. It has always been vacuum leaks including the MAP sensor vacuum line at the throttle body, leaking fuel pressure regulators dumping fuel into the intake manifold, bad grounds to the TPS and bad IAT temp sensors in the intake manifold.

The IAC is digital, never seen any test voltages published, and the complete Noid light test kits on Ebay have a noid light tester for the Jeep IAC!!!!

I totally overlooked the MAP sensor... I'll do physical inspections of fuel pressure regulators and I'll finish looking at the wiring before doing anything else.

It does still struggle to return to idle after being on the gas, especially in first gear and reverse. When I'm on the gas and let go, the idle dips down to about 250. Sometimes it'll return to normal idle, sometimes it'll idle at 250 and want to stall. I'm pretty sure my brother has one of those IAC test lights though.

I've got it pretty well narrowed down!! Thanks again

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[Ecomike]

I totally overlooked the MAP sensor... I'll do physical inspections of fuel pressure regulators and I'll finish looking at the wiring before doing anything else.

It does still struggle to return to idle after being on the gas, especially in first gear and reverse. When I'm on the gas and let go, the idle dips down to about 250. Sometimes it'll return to normal idle, sometimes it'll idle at 250 and want to stall. I'm pretty sure my brother has one of those IAC test lights though.

I've got it pretty well narrowed down!! Thanks again

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I thought you were saying it was idling high after stepping on the gas, idling low is another thing!!!!

 

[W1zardofozz]

I thought you were saying it was idling high after stepping on the gas, idling low is another thing!!!!

Okay, for clarity, when I press the gas, the rpm goes up nice and smooth. Normal, very normal. However, even I take my foot off the gas, the idle dips down to about 250 rpm but returns to normal idle after a second or two. However, often it'll remain at a 250 rpm idle. And very rarely it'll stall

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[Ecomike]

I'll test o2 sensors while I wait

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I just re-read this entire thread, my money is on damaged wires on the O2 sensor, shorted, on the power to the heater in the O2 sensor. Have you tested the O2 sensor yet? See my old thread on how to test O2 sensors, It can cause idle speed wander, hunting etc. Also clean and ohm test the Air intake temp sensor, it can affect idle speed big time!!!

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=sensor+test

 

[W1zardofozz]

I just re-read this entire thread, my money is on damaged wires on the O2 sensor, shorted, on the power to the heater in the O2 sensor. Have you tested the O2 sensor yet? See my old thread on how to test O2 sensors, It can cause idle speed wander, hunting etc. Also clean and ohm test the Air intake temp sensor, it can affect idle speed big time!!!

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=sensor+test

I'll give the wires a look. If I find nothing I'll read your thread. Also I'm going to use my brothers noid set to test the OAC just in case. You're a big help man, thank you so much

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[Ecomike]

While the IAC controls Idle speed, and can stick, it is controlled by the PCM computer, which makes control decisions based on all sensor data which depends on good wiring for good signals and good sensors!!!!

The engine also uses O2 sensor, MAP and IAT and CTS temperature control to control fuel rates which affect idle speed as well!!!!! These two can conflict at times causing wandering idles!!! IF the computer can not get proper Air/Fuel ratios from the O2 sensor it will operate the IAC and the fuel injectors at idle and hunt for the proper ratio and it uses all data form all those sensors make on the go estimates. Any air leaks past the IAC and throttle body throat thowe this process off. Also the O2 sensor is electrically heated at idle to make sure it gets accurate readings (it gets too cold at idle), no power to the O2 sensor heater, a poor ground, and or bad wiring on the sensor output to the PCM can cause the PCM to hunt for the proper idle speed and air/fuel ratio and never find it.

 

[Ecomike]

Lastly, the only place a voltage drop test is useful, is on the power wires to the starter that I know of. The only real way to properly test sensor grounds is using ohms, power off on the vehicle, testing from the sensor connector ground to the negative battery post. All sensor grounds should read less than 1 ohm.

The high ohm readings you got, if I understand your post correctly, were not accurate because the engine was powered up running and you had the injectors connected to the harness... etc. There must be no voltage or power on lines for resistance.

 

[Ecomike]

234k but the sensors are new. This is my third set, something keeps frying them. I'm thinking I have a short maybe. I've narrowed it down, because the same thing is frying my TPS since I'm on the 3rd one... It's something in that wiring harness, does anyone know where I can buy one?

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How do you know the sensors were fried? How did you test and verify they were fried?

 

[W1zardofozz]

Lastly, the only place a voltage drop test is useful, is on the power wires to the starter that I know of. The only real way to properly test sensor grounds is using ohms, power off on the vehicle, testing from the sensor connector ground to the negative battery post. All sensor grounds should read less than 1 ohm.

The high ohm readings you got, if I understand your post correctly, were not accurate because the engine was powered up running and you had the injectors connected to the harness... etc. There must be no voltage or power on lines for resistance.

The injectors tested fine all around just now work engine off. I've narrowed it down to the o2 sensors and possibly MAP. Fixing air leaks in my intake definitely helped. And replacing the ASD relay helped A LOT!! But it's still not perfect. We're getting there however! Doing testing as we speak

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[W1zardofozz]

How do you know the sensors were fried? How did you test and verify they were fried?

Oh I forgot to answer this one. I took the old parts to AutoZone and ohm tested them. When I saw the ohm readings were different, I'd replace it. I did this twice at AutoZone so I figured the sensors were just low quality. So I went to a dealership and got genuine sensors, and they went bad a well. This is my fourth set of sensors so I was thinking something in the harness was causing a short. I haven't had that happen for a while though

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[W1zardofozz]

I found some bent pins on my downstream oxygen sensor. Thus not allowing me to plug it in all the way. I'll pull a harness out of a junkyard tomorrow. Hope that helps also

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[Ecomike]

Oh I forgot to answer this one. I took the old parts to AutoZone and ohm tested them. When I saw the ohm readings were different, I'd replace it. I did this twice at AutoZone so I figured the sensors were just low quality. So I went to a dealership and got genuine sensors, and they went bad a well. This is my fourth set of sensors so I was thinking something in the harness was causing a short. I haven't had that happen for a while though

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You will never find a direct match reading on any two sensors. If one read 1000 ohms and the other 100 ohms then yes, but you check the readings when you buy the sensors, keep a log and see if the value changed later under the same exact conditions, such as temperature for temp sensors, I usually test mine in boiling water and ice water, or use a precise calibrated temp sensor and hot and cold water. Map sensor must be tested with a vacuum gauge reading the applied vacuum while the volt meter reads the voltage. Even then these values will vary from sensor to sensor and the computers learn the upper and lower range range limits of new sensors when installed and do their own calibration for the new sensors. No two sensors read the same for the same conditions. A bad sensor is one that reads way over or way under the OEM spec limits under the spec conditions (temp, vacuum, etc), or one that reads a limited range, not a wire enough range.

I had a TPS that had a spec range of .8 to 3.8 Volt from idle to WOT and it read .8 to 1.2

It would have tested OK using your method at .8 if I understand your process?

Edit: Down steam oxygen sensor has ZERO to do with engine idle or performance, it is only an EPA sniffer to verify that Cat converter and PCM fueling operations are working and that the cat has the right amount of O2 to confirm the engine is not dumping fuel into the exhaust. But it may have a common ground and O2 sensor heater power supply!!!! It may have caused issues with readings on the front upstream O2 sensor if it caused a short there?

 

[Ecomike]

I found some bent pins on my downstream oxygen sensor. Thus not allowing me to plug it in all the way. I'll pull a harness out of a junkyard tomorrow. Hope that helps also

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That should have thrown an OBD-II code, are you sure there are no codes? Is the check engine light working?

 

[W1zardofozz]

That should have thrown an OBD-II code, are you sure there are no codes? Is the check engine light working?

CEL is certainly working because it threw a code for the TPS recently and a while ago for the Cam Position Sensor. That was with an actual OBDII scanner. When I did the jeeps odometer trick, it threw code 12 (bat. disconnect), 42 (ASD relay), and 45 (turbo??) Then it threw out 55. However, the heater circuit on both oxygen sensors read 0 v... Shouldn't it read 12 v? I did it with engine on and engine off just to make sure. I even used 2 different meters

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[W1zardofozz]

I just double checked and it threw code 35 just now, meaning open circuit or short in the cooling fan circuit. I'll check that as well. She's gradually running better though

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[W1zardofozz]

Here's the full code list it just threw:
12 battery disconnect

35 cooling fan circuit open or shorted

42 An open or shorted condition detected in the auto shutdown relay circuit. An open condition detected in the ASD relay output circuit. An open or shorted condition detected in the fuel pump relay control circuit. An open circuit between PCM and fuel gauge sending unit. Circuit shorted to voltage between PCM and fuel gauge sending unit. No movement of fuel level sender detected

43 Peak primary circuit current not achieved with maximum dwell time. Misfire detected in one or more cylinders 1 thru 6. (4 and 6 cyls).

45 no idea honestly

21 Oxygen sensor detection neither rich or lean

-OR-

Oxygen sensor input voltage stayed above normal operating range.

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[W1zardofozz]

Out didn't throw these last night, so maybe it just picked them up??

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[W1zardofozz]

Anyways, it's definitely running a hell of a lot better now

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