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Old 06-02-2010, 07:10 PM   #1
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Stuck Choke?

Hi All,
I have '98 TJ that is a great vehicle but it has an annoying problem. From a cold start, it fires right up no...no problem. You can head off down the down the road or let it idle in the driveway and then, after about 3 to 4 minutes, it starts to choke itself out and wants to die. If I shut it off and then immediately start it back up then it runs great! That is, until the engine gets cold and then you start the process all over again.
I took off the air cleaner and then watched the "butterfly" (what I am calling the choke). From a cold start, while the Jeep warms up, the choke never opens and then if I shut it off and start it again (while hot) the choke "stands to attention" and opens right up!
On the side of the throttle-body, connected to the choke is a little black box (what's it called?) that looks like a solenoid or a coil. Could that be the problem?
As a side-note, I took it to a Jeep Dealer. They said it was an oxygen sensor. A new sensor and $170 bucks later...same problem.
Any help is appreciated. Thanks.
Mark

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Old 06-02-2010, 07:21 PM   #2
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Fuel injected vehicles don't have chokes, a choke is something only older carbureted engines have. The valve plate you have found is not a choke at all. That valve plate only opens when you step on the accelerator pedal and is what lets all the engine air in at other than idle rpms. At idle, the engine instead gets all its air through the IAC (Idle Air Control module) when you are not stepping on the accelerator pedal. A sticky/dirty IAC can cause that kind of problem.

Cleaning the throttle body's interior with an aerosol throttle body cleaner while the engine running is the best way to likely fix the issue. Just make sure to direct some of the spray into the IAC's air passage inlet just above the butterfly valve plate which is where the IAC gets its air when the engine is at idle.
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Old 06-02-2010, 07:26 PM   #3
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x2 -- My IAC acts up from time to time. It can make your throttle "stick" open, cause rough/sporadic idling, and a few other things. Very annoying but easy to fix with a little cleaning, and if all fails, it's a replaceable module.
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Old 06-02-2010, 07:30 PM   #4
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If cleaning it through the throttle body doesn't work like suggested above, it is easily cleaned more thoroughly by simply removing it from the throttle body. Only two small torx-head screws hold it to the throttle body. It normally only gets dirty and is cleanable to restore it to good operation. I haven't heard of one that actually went bad yet.
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Old 06-02-2010, 07:42 PM   #5
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Stuck Choke Reply

Man. You guys are awesome. Even a picture! Dang.
I did a little more research and a TPS and CPS were mentioned. But, you don't think that either of these replacements are necessary?
Thanks for the help.
Mark
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Old 06-02-2010, 07:50 PM   #6
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TPS could be the problem but it sounds more like the IAC to me. Besides, you only need to clean the IAC first to see if that cures the problem. But the TPS (throttle position sensor) cannot be cleaned, it can only be replaced when it goes bad. I would not give a second thought to the CPS.
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Old 06-07-2010, 08:45 PM   #7
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Stuck Choke Continued

Well, I swapped the IAC this weekend and cleaned the throttle body. It was easy to do and thank you all for all of your help but it did not fix the problem.
It is still doing the same thing. As soon as it reaches operating temperature it coughs, chokes and looses power. Then I can either feather the pedal (rev it up) until the power comes back in about ten seconds or I can turn it off and turn it on again. Then the engine is fine until it cools down again and it starts all over again. Its a pain when you temporarily lose power in traffic.
I did a little more research and, basically, it comes down to one of these items: the IAC, TPS, CPS or the MAP.
I just swapped the IAC. Which one should I try next? My guess is either the CPS or the TPS.
Any help is appreciated.
~Mark
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Old 06-07-2010, 08:56 PM   #8
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Coolant temperature sender? Starts fine because it thinks it is cold. (and it is right) Starts to warm up but the computer doesn't know that and thinks it is still cold. So the mixture stays rich and when it gets warmed up is too rich and it runs poorly. It would run just like a carbureted car when you leave the choke on too long.

If you are saying that just shutting it off and then turning it back on cures the problem for the rest of the drive, then this is not a great suggestion. The performance of the sensor can be checked with an ohm meter in place, so it doesn't take long to check it and you don't need to buy the part unless it is bad.
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Old 06-07-2010, 09:07 PM   #9
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I don't think its the sender. Turning it off, then on, does solve the problem temporarily and it runs great as soon as the throttle-opening figures out where it needs to be.
It is a good suggestion though and I think that the temp sensor is an inexpensive part if I want to swap it later.
Thanks.
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Old 06-07-2010, 09:15 PM   #10
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Hmmm. No codes? Replacing parts and hoping to get lucky gets expensive.
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Old 06-07-2010, 09:31 PM   #11
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The first thing that I did was to take it to a Chrysler dealer. The only code that they got was an O2 sensor. They replaced it for $170 bucks but the problem remains. The way I see it, I can replace 3 parts and take my best shot for the same $170 if I do it myself and get the advice of folks like you.
But your suggestion is valid and I have a friend who owns a mech shop. I can take it to him an he will check the codes again for me for $10.
Thanks. Don't give up and I won't !!
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Old 11-28-2010, 06:14 PM   #12
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i am having the same problem as Mark is. i did some tune up stuff like the spark plugs,cleaned the throttle plate,cleaned the injectors and i even took out the IAC and cleaned that. is the IAC supposed to come apart? mine was in four sections. the IAC body,a spring,a shield for the spring and the pointy part(that's a technical term) which has some threads on it. was that supposed to come apart? lol
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Old 11-28-2010, 06:23 PM   #13
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Quote:
Originally Posted by Leeroy Jeepkins View Post
is the IAC supposed to come apart? mine was in four sections. the IAC body,a spring,a shield for the spring and the pointy part(that's a technical term) which has some threads on it. was that supposed to come apart? lol
Uh, I don't think so. But maybe you can put it back together since it is threaded. If the Jeep idles ok afterwards, the IAC is probably ok.
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Old 11-28-2010, 06:26 PM   #14
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How many miles are on your Jeep? I'm wondering 2 things.

1-Is your catalytic converter plugged up. Though the fact that restarting it solves the problem points away from that.

2-Have you checked out your coil? I have had vehicles in the past that had periodic issues, it was the coil heating up - it had an internal crack.

The fact that restarting it solves the problem is odd though.
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Old 11-28-2010, 06:29 PM   #15
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Quote:
i am having the same problem as Mark is. i did some tune up stuff like the spark plugs,cleaned the throttle plate,cleaned the injectors and i even took out the IAC and cleaned that. is the IAC supposed to come apart? mine was in four sections. the IAC body,a spring,a shield for the spring and the pointy part(that's a technical term) which has some threads on it. was that supposed to come apart? lol
Definitely not normal...i've been told if you take out the IAC...you should be very gentle with it and don't push, pull, or twist the plunger or you'll destroy it.
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Old 11-28-2010, 06:36 PM   #16
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ahhh.i pushed,pulled and twisted the plunger.it won't thread back in all that tight now. looks like i'm going to get another one tomorrow.

Subtlez. what coil are you talking about?(sorry,i'm not the best when it comes to this stuff)

when i put it back in it idled very low around 250 rpm's so i shut it off and when i started it back up it idled around 700.
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Old 11-28-2010, 07:24 PM   #17
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my jeep has 123,000 miles on it. i have never tried to shut it down when it bogs on me.it usually goes away after about 20 seconds. it may be the catalytic converter?
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Old 11-29-2010, 10:25 AM   #18
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replaced the (now broken) IAC this morning and it's still doing it. i'm assuming the last two options are the o2 sensor or the cat converter.
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Old 11-29-2010, 06:27 PM   #19
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ok. i was trying to loosen the o2 sensor but i didn't have any luck.on my way to pick up a diagnostic scanner my check engine light comes on.i buy the scanner and go out to my jeep and plug it in. it says i have an issue with my o2 sensor. i go out, buy a bigger wrench and i get the o2 sensor off. i installed a new sensor and reset my check engine light. guess what? no more sputter and no more crazy idle. fixed!!!! thank you soooo much guys!!! sure i broke some stuff and did some maintenance that may or may not have been needed but i have never worked on a car before aside from the oil and wiper blades and i fixed it. i am so proud of myself.lol. i do commercial HVAC work for a living and i am somewhat mechanically inclined but i never bothered to look under the hood. i feel really really good right now.

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