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Old 01-12-2014, 10:36 PM   #1
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Rough idle/dies after starting

Okay, I've been trying to follow other people that have this same problem, but I am at the point I need my own thread. Trying to off-road on Saturday, has to be fixed by then. Here's the long-version:

So for a couple weeks now I have had idle/start problems. It's inconsistent. The main issue is that my jeep will die right after starting, or, if it does start, the idle will be rough/low. Around 500 rpm. But it is off and on, not consistent. No problems when driving normal speeds.

The first thing I did was remove/clean the throttle body. This seemed to fix it for 2 days, then back to crap.

After unplugging the IAC and the TPS it threw a code for a bad TPS. I replaced the TPS with no major improvement.

My battery happened to be bad, so I replaced the battery. This "fixed" it for another few days.

Tonight I checked my fuel pressure and my fuel pressure was good at key-on and idle. Both when the engine started up fine, and when it idled rough. It also didn't drop too much after waiting 30 minutes.

When I unplugged my IAC tonight, for it to run in limp mode, it started fine (but then ran in limp mode).

The only other weird thing is that sometimes I can put it in drive and the car won't die until I'm backed out of my parking spot or pulled forward a few feet. Once it died after I went down my whole street.

I tried listening for air leaks with a stethoscope, and I think I heard air escaping from under the spring that controls my throttle butterfly valve.

Thoughts? Suggestions? Pointers? Maybe just an elimination check to narrow it down? Thanks for your help forum-mates!

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Old 01-12-2014, 10:45 PM   #2
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I would try the camshaft position sensor. Just what I would do if it was mine. It monitors engine speed. My first thought would be the TPS you already changed. I have never had this issue just thoughts hoping someone that had the issue sounds off. Good luck.

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Old 01-12-2014, 10:45 PM   #3
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I am having very similar issues currently with my '01 Sahara. I only experience this problem when the engine is cold and its only the first few minutes after start up and it is sporadic, not happening all the time. I Have an O2 sensor code coming up saying my upstream O2 sensor is bad. I plan on replacing both of them and seeing if that eliminates the problem. Other suggestions I've heard are cleaning the throttle body and the IAC or maybe checking spark plugs. Let me know what you find out and I'll do the same. Hope the suggestions help!
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Old 01-12-2014, 10:47 PM   #4
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Quote:
Originally Posted by Higher Pursuit View Post
I am having very similar issues currently with my '01 Sahara. I only experience this problem when the engine is cold and its only the first few minutes after start up and it is sporadic, not happening all the time. I Have an O2 sensor code coming up saying my upstream O2 sensor is bad. I plan on replacing both of them and seeing if that eliminates the problem. Other suggestions I've heard are cleaning the throttle body and the IAC or maybe checking spark plugs. Let me know what you find out and I'll do the same. Hope the suggestions help!
Not a fix but an idea. The engine runs off preset settings while cold. Then switches to the sensors when warm.
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Old 01-13-2014, 10:27 PM   #5
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Update: I found a split in the crank case vent tube where it connects to the intake. Since autozone and company don't carry a spare and the dealership won't have one in until Wednesday, I am currently running on electrical tape and humming along. Further updates as things develop.
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Old 01-14-2014, 01:26 AM   #6
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Try spraying around the throttle body and manifold with carb clean to check for leaks it should idle up due to it having more fuel to burn if there is a leak. But I dont think a vaccum leak is the problem cause the system does not monitor incoming I.e. no maf sensor. If there was a vaccumm leak it would have a high idle, I would be looking more at the iac. You said when you replaced the battery it ran ok? When you disconnected the battery the system reset (ran ok) then after it learned some of its parrameters it ran bad? Try cleaning the iac and/or tapping on it while it is running to see if idle changes
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Old 01-14-2014, 02:41 AM   #7
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I've cleaned the IAC twice. Once initially, when I first cleaned the throttle body, and again to make sure it was really good and clean. Both times it was "fixed" for a little after then went back to bad. I'm leaning toward replacing the IAC next. I just don't want to pay $80 to not fix the problem. I'll try tapping on it tomorrow and see if that makes any change occur. Thanks again for the suggestions!
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Old 01-14-2014, 11:31 PM   #8
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Should get in the new crank case vent tube tomorrow. Tonight I sprayed it with cleaner. No vacuum leaks popped up. Still searching for a solution . . .
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Old 01-14-2014, 11:32 PM   #9
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If you dont notice a change by tapping on it you might be best off getting a shop to diag it so they can see if the iac is working properly. It does sound like it could be the iac but if not theres $80 for a part not needed where as shop diag $100? + the part that is actually needed, could be under $200. But if you thow several $100 parts at it it could get well over that cost of shop diag. I do understand wanting to do the work yourself but without knowing what is actually going on with a scan tool your just throwing parts at it. Do you have a good digital multi meter?
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Old 01-14-2014, 11:36 PM   #10
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Also do you have factory a/c when swithed on the iac will open slightly more to compensate for the added load of the a/c it should idle up a couple hundred rpm. Not sure if you can get it to run long enough to test that so you might try disconnecting the battery to reset the system first.
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Old 01-15-2014, 08:41 AM   #11
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Sounds like a fuel pump issue to me ... but you said your fuel pressure was fine...
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Old 01-15-2014, 02:18 PM   #12
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I have a/c. I'll try turning it on tonight to see if it changes anything. Since I taped up my crank case vent tube, the jeep hasn't stalled anymore, but is still idling heavy. I hear you on throwing parts at it. I do have a multimeter.
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Old 01-17-2014, 12:05 AM   #13
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Replaced my crank case vent tube. So far so good, haven't been able to tap on the IAC with a hammer yet, since every time I have a hammer, the idle isn't dropping (figures). I'll hopefully try the hammer-tap tomorrow.

Fingers still crossed that replacing the vent tube tonight fixed everything!
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Old 01-17-2014, 01:03 AM   #14
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Wouldnt go at it with a hammer to much leverage, use the handle of a screwdriver. But it sounds like it might be fixed.
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Old 01-17-2014, 10:26 AM   #15
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Haha, yeah. Only light tapping, whatever the tool. Engine sounds like it's running better, and doesn't die after starting anymore, but still low idles. I have a tool with me today, so after work if it low idles I'll give it a few gentle taps. Thanks again for the support, I'll let you know. Fingers crossed for IAC!
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Old 01-21-2014, 08:51 PM   #16
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Okay guys, here's the update. Problem seemed to be all but fixed. I went wheelin this weekend in TX, and had no issues. But then last night and today, it was back in full force with the car stalling out right after starting. It is cold now and it wasn't this weekend. The other thing I'm noticing is that my heater will run cold mid-drive, then heat back up again, but generally doesn't seem as hot as it used to be. Also, I tapped on the IAC and saw no change.
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Old 02-08-2014, 02:21 PM   #17
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Final Update. Replaced the IAC (idle air control) after a trip to the mechanic and everything is running smooth again. Thanks for all the support!

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