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  #1  
Old 03-23-2017, 09:36 AM
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Another 4.7 rough idle /warm start problem

Okay, so here it goes. My 04, 4.7 has a rough idle on warm start issue. Here's what I've done to address it thus far. New IAC, New TPS, complete cleaning of throttle body and bg44k intake combustion cleaner, with complete tune-up and oil change. The engine starts fine during cold weather and being in NY it's really a non-issue during the winter month's so long as the temperature is below 32 degrees or so. The problem is seen after warm-up during restarts if engine hasn't cooled down. Ex: warm weather cold start with vehicle sitting overnight starts and idles fine. Drive Jeep to local store, shop for 30 minutes come back out start vehicle and "viola" rough idle! Drive Jeep home, sits in driveway for an hr. "Viola" starts fine! Jeep has thrown several codes for rough idle or a cylinder misfire which have cleared themselves after several miles of driving?
I've also read maybe sticky valves? And or possibly MAP sensor, any help or input is appreciated.

MacDaddy

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  #2  
Old 03-23-2017, 12:08 PM
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Re: Another 4.7 rough idle /warm start problem

I would start with a seafoam threatment through the brake booster vacum line, to clean the valve stems and prevent them from sticking. When really dirty, you will have to do it more then once.
Some other problem can be with the inlet air temp sensor. Do you have a scanner with live data to see what the sensors read?
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Old 03-23-2017, 07:45 PM
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Re: Another 4.7 rough idle /warm start problem

No scanner at home but can obtain from local shop, I do have slight valve tap on start which diminishes with warm-up. Had to replace exhaust manifold studs due to leak (typical) and I'm wondering if it could be burnt exhaust valve? 140,000+ on odometer and thinking valve job?
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Old 03-23-2017, 08:28 PM
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Re: Another 4.7 rough idle /warm start problem

Is the slight valve tap not caused by the hydraulic lash adjuster(s)? Did you do a compression check already?
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Old 03-24-2017, 06:56 AM
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Re: Another 4.7 rough idle /warm start problem

Yes to compression check and no to valve lash adjuster. I'm going to check IAT voltage and MAP sensor they're the least expensive fix and if that doesn't correct it then move onto the heads. Thanks for your input because I completely overlooked the IAT as a possible culprit. I'll post and let you know what I find out. Thanks again, MacDaddy.
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Old 03-25-2017, 04:51 AM
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Re: Another 4.7 rough idle /warm start problem

I have similar issue. Sometimes I have to crank excessively to get it to sputter. I wonder if my injector o-ring are shit as I rebuilt my engine but reused the O rings
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Old 03-29-2017, 08:37 AM
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Re: Another 4.7 rough idle /warm start problem

Well, figured it out, and thanks to Frank, (Frango100) it was a simple case of the IAT sensor 26 bucks and 5 mins and it seems to be cured, thanks again as I completely overlooked the IAT...
MacDaddy
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Old 03-29-2017, 08:44 AM
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Re: Another 4.7 rough idle /warm start problem

I think the 0-rings should have definitely been replaced and does seem to be starving for fuel or spark. Remember three things it needs to run, suck, bang and blow. (Fuel, ignition, exhaust)
MacDaddy
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Old 03-29-2017, 09:16 AM
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Re: Another 4.7 rough idle /warm start problem

Quote:
Originally Posted by MacDaddy View Post
Well, figured it out, and thanks to Frank, (Frango100) it was a simple case of the IAT sensor 26 bucks and 5 mins and it seems to be cured, thanks again as I completely overlooked the IAT...
MacDaddy
Get oem sensor?


Somewhere i read on this forum that oem parts are the best thing this truck can benefit from
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Old 03-29-2017, 12:57 PM
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Re: Another 4.7 rough idle /warm start problem

Good to hear its fixed MacDaddy. Did you see the output from the old IAT sensor, or you just changed it?

---------- Post added at 02:57 PM ---------- Previous post was at 02:53 PM ----------

Quote:
Originally Posted by hoffmanestates View Post
I have similar issue. Sometimes I have to crank excessively to get it to sputter. I wonder if my injector o-ring are shit as I rebuilt my engine but reused the O rings
The O-rings on the pressure side must be ok, or you will have a fuel leak. A bad O-ring on the other side could give some false air to enter the inlet, but it should be completely missing or broken in half before I would expect any influence.
Does your jeep always start hard, cold and hot? Priming the fuel system does anything?
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Old 03-29-2017, 01:19 PM
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Re: Another 4.7 rough idle /warm start problem

It happens when ever how ever.

It might not happen all week and then out of nowhere Saturday it struggles to start. And be fine for a few days.

There are times it will struggle each time you need to restart. Within a day
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Old 03-30-2017, 12:44 PM
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Re: Another 4.7 rough idle /warm start problem

Struggles during re-start, so does it start fine when cold? When it starts, does it run smooth? Did you check the live data of the engine air inlet sensor and the MAP? It could be a problem of moisture in a connector.
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