Low idle to stalling when stopped - JeepForum.com
 
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post #1 of 14 Old 02-01-2010, 09:17 AM Thread Starter
gotmudd1
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Low idle to stalling when stopped

guys, I need your help with an idle issue when stopped or coming to a stop

After start up for about 3 days now the RPM's do not get above the first hash mark on the gauge even once the engine temp is at normal. And when coming to a stop the engine wants to stall and does if I do not give it gas. I am guessing this is some kind of sensor but need your advice.

What could cause this and how do I fix it?

Some info if needed.
New plugs, wires, cap and rotor installed last summer
Throttle body was cleaned also during that time- just the butterfly though

Thanks,
Bryan


97 Wrangler: 4.0L, 5 speed, BB, 31's KM2's, CAI, Cat-Back Exhaust
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post #2 of 14 Old 02-01-2010, 09:26 AM
Jerry Bransford
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Clean your IAC (idle air controller) which is mounted onto your throttle body. It's held to the TB by two torx screws (T-25 IIRC) & comes off easily. Gently clean its solenoid actuated control rod with either carb cleaner or TB cleaner & a rag/toothbrush. Clean the hole in the TB its control rod fits into too. The engine gets ALL of its air via the IAC at idle so when it sticks, and they do get dirty & stick, a bad idle is the result.

After you're done cleaning the IAC, use the rest of the can of TB (or carb) cleaner to clean your TB's interior. The instructions on the can will tell you how.
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TB & TPS Sensor Locations.jpg  

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post #3 of 14 Old 02-01-2010, 09:29 AM Thread Starter
gotmudd1
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Great, I will try this. thanks for the quick reply

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post #4 of 14 Old 02-01-2010, 09:37 AM
Jerry Bransford
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If that doesn't do it, but it should, the other possibility is the TPS (throttle position sensor) which is also mounted on the throttle body. However, the TPS needs to be replaced when it goes bad, it can't be cleaned like the IAC can. Good luck.

P.S. The two small torx-head machine screws that hold the IAC to the throttle body are tight & held in place by locktite. So make sure to keep the torx head bit straight in the screw head and hold it in firmly so it can't slip out & strip out the screw head. I use a 1/4" ratchet wrench for these two screws for more torque instead of a screwdriver handle. Use a good sharp unworn torx bit too, a worn torx bit is likely to strip out the screw head.

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post #5 of 14 Old 02-01-2010, 01:25 PM
garbon2535
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Thoroughly cleaning your IAC motor and TB is definitely the cheapest and easiest thing you can do first.

I had this problem last fall. As Jerry said I would very thoroughly clean your TB and IAC motor. I would first remove the TB. After you remove the TB it's a lot easier to remove the IAC motor (I could not reach the lower screw on the IAC motor without removing the entire TB assembly). Clean the IAC motor and the hole on the TB that it mounts to. I used q-tip's to get into the small opening. Mine was extremely dirty. FYI... I went through 1-1/2 cans of TB cleaner cleaning my TB and IAC motor.

When you are sitting at an idle, if you turn on your heater or A/C (if you have a/c) do the RPM's increase at all? Your engine RPM's should increase to compensate for the increased load. If your engine RPM's do not increase it could be that your IAC motor is not working properly. It is about $60 to replace your IAC motor if needed.
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post #6 of 14 Old 02-03-2010, 07:45 AM Thread Starter
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Alright, i spent last night thoroughly cleaning my IAC, TB and TPS. Last night it started and seemed fine when I took it around the block. However, on my way to work the problem happened again. What do I look for now?

If it was one of the sensors which one is more likely to go? I want to avoid replacing everything to find the cause.

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post #7 of 14 Old 02-03-2010, 08:10 AM
garbon2535
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The IAC motor is what controls the airflow to the motor during idle. I would trying replacing the IAC motor. If that doesn't do it, the IAC motor is easy to take back out and return to the store.

I had the same problem last fall. I cleaned my IAC motor and TB very good. It helped a lot but it did not solve the problem 100%. I had low RPM's at idle. After running around a few weeks after cleaning everything it started to get worse so i replaced the IAC motor. That solved my problem.
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post #8 of 14 Old 02-03-2010, 09:17 AM Thread Starter
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So it can only be the IAC or the TPS sensor that would cause this issue?

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post #9 of 14 Old 02-03-2010, 09:46 AM
Jerry Bransford
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"Only" is a tough word to accept. The IAC or TPS are the most likely sources of this kind of problem.

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post #10 of 14 Old 02-03-2010, 10:26 AM Thread Starter
gotmudd1
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thanks, i figured "only" was wishful thinking to

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post #11 of 14 Old 02-03-2010, 01:27 PM
garbon2535
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Here is what the FSM has to say regarding the condition: ENGINE STALLS OR ROUGH IDLE

1. Carbon build-up on throttle plate
-Remove TB & de-carbon

2. Engine idle speed too low
-Check IAC motor

3. Worn or incorrectly gapped spark plugs
-Replace or clean and re-gap spark plugs

4. Worn or burned distributor rotor
-Install new distributor rotor

5.Spark plug cables defective or crossed
-Check for correct firing order or replace spark plug cables

6. Faulty coil
-Test and replace, if necessary

7. Intake manifold vacuum leak
-Inspect intake manifold gasket and vacuum hoses, replace if necessary

8. EGR valve leaking or stuck open
-Test and replace, if necessary
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post #12 of 14 Old 02-03-2010, 02:45 PM
Jerry Bransford
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I'm surprised the FSM doesn't include a bad TPS as one of the potential causes of a rough idle. My TJ had a very bad idle & erratic acceleration years ago & it was a bad TPS.

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post #13 of 14 Old 02-03-2010, 06:26 PM
garbon2535
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Quote:
Originally Posted by Jerry Bransford View Post
I'm surprised the FSM doesn't include a bad TPS as one of the potential causes of a rough idle. My TJ had a very bad idle & erratic acceleration years ago & it was a bad TPS.
Did you have an error code for the TPS when this happened?
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post #14 of 14 Old 02-03-2010, 06:32 PM
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Quote:
Originally Posted by garbon2535 View Post
Did you have an error code for the TPS when this happened?
No.

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