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Old 10-10-2012, 07:22 AM
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Unhappy rough tick over and running

Hi, I've suddenly got a problem with my 4.7 v8 Grand Cherokee (year 2000) where the engine will start up fine, hold a good tick over from cold for about a minute or so until the temperature gauge starts to rise.

Then the revs drop to about 500 and it feels like it's missing, if you give it gas it still runs rough even when driving.

The problem has only just started, this week I've changed the air filter to a K&N one and the engine ran fine.

Then yesterday I changed the rear section of the exhaust (cat back) with a more free flowing one. Sounds great and ran well all day, then after stopping at a store for while when I came back it started up and then went rough on me.

Any ideas?

So far I've taken the throttle body off and given it a good clean, taken the Idle air motor off and cleaned it out. should you be able to take it apart and should the piston thing move freely or not?

Next I'm going to pull the plugs and check them, guess I should have checked them first but cant find my plug socket.

So if you guys have any ideas, please let me know. I live in the UK, parts are hard to find over here other than a main dealer or eBay... hope this isn't going to cost mega bucks.

Gary.
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Old 10-10-2012, 12:21 PM
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Re: rough tick over and running

Ok, done the plugs.... Still rough when warm. It runs sweet when cold until it gets to just under 40 on the gauge then something happens and the revs drop off to 500 and it's a bag of crap to drive.

Any ideas guys?

Gary @confused.com
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Old 10-10-2012, 05:22 PM
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Re: rough tick over and running

Just checked out the error codes (although I've had no check engine light on the dash). Had a whole bunch of codes...
P0201 through to p0208 (injectors 1 to 8)
P0123 (throttle position sensor)
P0152 (O2 Sensor Circuit High Voltage)
P0505 (Idle air control).

I take it (hope) one problem is causing the error codes of the others?

Come to think of it, not sure if these are all new error codes ore some old ones? Not had the jeep too long, how do i clear down the codes?

Gary.
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Old 10-11-2012, 11:21 AM
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Re: rough tick over and running

P0505 was probably from you having it unplugged inspecting it. The TPS code is likely the same although the p0201 injector fault is an indication your TPS is bad. Feedback from a failing TPS in the PCM causes the injector fault codes. The TPS will cause a wondering idle, you may notice the torque converter unlock driving down the freeway (holding steady rpms with steady throttle then the rpms just rise for no reason). Also harsh shifts can be noted sometimes.

Your running rough when warm is likely from the p0152, If your o2 is open or shorted to power it cannot adjust fuel strategy thus running like anus and it doesnt know any better... The problem is *likely* your o2 sensor but inspect the wiring near by if you can.
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Old 10-11-2012, 03:24 PM
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Re: rough tick over and running

Ok thanks, I'll give the 02 a seeing to when next of shift on Sunday.
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Old 10-12-2012, 09:52 PM
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Sweet smell tail pipe? Coolant missing? My 02 ran with 3 o2 sensors tainted with coolant for about 3 weeks.

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Old 10-13-2012, 10:12 AM
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Re: rough tick over and running

Regarding the idle air stepper motor, you should NOT be able to turn the plunjer by hand. If you can do so, the stepper motor will not be able to adjust the plunjer, since it can rotate together with the motor. There are 2 small plastic tabs, which should hold the plunjer from rotating, but they are very weak and break of easily when you try to turn the plunjer by hand (during cleaning for example).
But your idle problem is most probably caused by the O2 sensor. In the warmup mode, the PCM controls the fuel in open loop and thus doesn´t look at the O2 sensors. Then when it is warmed up, it goes into closed loop mode, also in idle, using the O2 sensor inputs to fine tune the fuel/air ratio.
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Old 10-14-2012, 01:43 AM
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Re: rough tick over and running

Quote:
Originally Posted by 2005JGC View Post
If your o2 is open or shorted to power it cannot adjust fuel strategy thus running like anus and it doesnt know any better...
Wow, I'm sure it's because I'm ridiculously tired but that comment had me cracking up. People walking by my office window probably think I'm loosing my mind. Thanks for that.
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Old 10-14-2012, 05:45 AM
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Re: rough tick over and running

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Originally Posted by hoffmanestates View Post
Sweet smell tail pipe? Coolant missing? My 02 ran with 3 o2 sensors tainted with coolant for about 3 weeks.

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Hi,

Nope, the pipe smells normal and coolant is still where it should be.
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Old 10-14-2012, 05:48 AM
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Re: rough tick over and running

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Originally Posted by Dustinmk4 View Post
Wow, I'm sure it's because I'm ridiculously tired but that comment had me cracking up. People walking by my office window probably think I'm loosing my mind. Thanks for that.
Yeah I've had running anus before, not nice.
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Old 10-14-2012, 05:58 AM
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Re: rough tick over and running

Quote:
Originally Posted by Frango100 View Post
Regarding the idle air stepper motor, you should NOT be able to turn the plunjer by hand. If you can do so, the stepper motor will not be able to adjust the plunjer, since it can rotate together with the motor. There are 2 small plastic tabs, which should hold the plunjer from rotating, but they are very weak and break of easily when you try to turn the plunjer by hand (during cleaning for example).
But your idle problem is most probably caused by the O2 sensor. In the warmup mode, the PCM controls the fuel in open loop and thus doesn´t look at the O2 sensors. Then when it is warmed up, it goes into closed loop mode, also in idle, using the O2 sensor inputs to fine tune the fuel/air ratio.
Hi, Ok looks like the IA motor is toast then as i had it in bit cleaning it. A new one of them to buy tomorrow then.
As for the O2 sensor, maybe it got damaged or a wire loose when I attacked the rear box of the exhausts with a hammer trying to get it off when I replaced it earlier in the day. Time to go crawl under the truck.

Thanks for the help so far guys, much appreciated... So much nicer to get some real life experienced help than from service garages over here that know nothing about Jeeps and rape your wallet finding out what's wrong.

Thanks guys, I'll keep you posted.
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Old 10-14-2012, 12:15 PM
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Re: rough tick over and running

Mmmmm... Been out and poked and prodded around on things under the truck and hood to see if anything is loose, no joy still had the rough running and idle. Even died a couple of times. disconnected the battery to clear all the codes that i made by disconnecting and reconnecting stuff, when i reconnected the battery i thought id git it one more go. Well it started smooth, revs calmed down then dropped right down low. I thought it was going to stall again but it suddenly picked back up and smoothed out, it stayed like that so i gave it some beans and the revs were sweet. Took it for a spin and everything looks fine, whatever was wrong looks to have cleared up.

Happy for now.
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