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Mr Chill 04-24-2012 01:09 AM

Going after poor idle on 4.7... Anything else?
This is an '05 4.7 with ~120k.

Just tonight the wife reported a bumbling idle while parked. She revved it and it died moments later. No problems on the highway or at stoplights in drive, just while parked.

My first thought was dirty iacv. So i'm putting together a little r&r list...

- Inspect throttle body, remove and clean if needed
- Remove and clean iacv
- Replace pcv valve
- Inspect/r&r coils and install new plugs
- Maybe Seafoam and an oil change just because...

Anything else you all suggest while I'm in there and getting dirty?

Does this sound at all egr-related?

We've had this Jeep for right at a week now, and I'm new to the 4.7. Any input is appreciated. Looking to do this as soon as Wednesday morning. Thanks!

FlyinRyan 04-24-2012 01:29 AM

Re: Going after poor idle on 4.7... Anything else?
IACV, and EGR should be at the top of the list, coils near the bottom. use the vacuum line going to the brake booster for the Seafoam, better distribution amongst the cylinders that way.

2005JGC 04-24-2012 02:19 AM

Re: Going after poor idle on 4.7... Anything else?
A failing throttle position sensor is VERY VERY VERY common on the 4.7l... not sure why its so common on just the 4.7l but I see quite a few, causes a wondering idle, sometimes dtc's (rarely) can cause trans shifting concerns, and occasionally die out. If your going to start somewhere, this is cheaper than an egr valve (also a good suggestion) so a good place to start.

One thing you can try is start the vehicle and grab the connector on the Throttle Position Sensor firmly and flex the sensor around (up and down) obviously your not going to actually make it actually flex around just when applying this pressure if your idle starts to fluctuate replace your tps no matter what, regardless of if it is the actual concern, this is an indication of failure, you can even do this test again with the new one and will see your idle will stay rock solid.

Mr Chill 04-24-2012 02:57 AM

Re: Going after poor idle on 4.7... Anything else?
Thanks for putting this in the appropriate category. I had a bad tps on my '97 ZJ 4.0 and it caused a much different problem (surging/bucking on accel), but i'll definitely check this one out!

Idk how I didn't notice this before, but it looks like someone has plasti-welded the pcv valve together. Like they broke it at the bend and didn't feel like installing another one. Wow. Can't wait to find what else this "1-owner, dealer-serviced" Jeep has in store for me. They tried hard to make it look good too, using black plasti-weld and smoothing it out all nice and neat...

05rockymountain 04-29-2012 11:36 AM

Re: Going after poor idle on 4.7... Anything else?
I have been chasing similiar problems on my 05,no codes were present ,I had replaced tps,did the sea foam mosquito fogger procedure,cleaned iac throttle body ,plugs ,filters,then i took a guess at egr valve and it solved my issues. the egr valve had a lot of carbon in it ,and gasket was burnt ,see my post,"egr failure with no codes"in wk troubleshooting for all the symptoms i got,got a "standard" brand egr,so far so good ,seems like egr issues are common on these.

hummer recovery team 07-21-2012 10:54 PM

Re: Going after poor idle on 4.7... Anything else?
Egr fixed trans surging too! id start there

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