RPM not super steady?

Here's a question I'll put to the forum. The XK has never really idled very steadily. Most of the time its not bad but sometimes hunts around a little bit. Anyone else ever have this issue? It doesn't cause any problems and it's not drastic by any means but the lights will dim a little cause it'll idle really low and waiver around. It almost seems like it's too low in general.
Ideas?

P.S. I feel almost guilty for the amount of time i've been looking at the Subaru forum for my forester. I'm not used to having so many options on everything!! I can read for hours.

I have the 4.7l as well and have always had a very steady idle. In fact, when I first bought it there were times sitting at a stop light that I could barely tell the engine was running.

I only notice the slight fluctuation in RPMs when the AC compressor kicks on and off. Have you tried cleaning the IAC valve to see if that has any affect?

Every once in a while it wandered a bit - but rarely happens after I installed the Jet Stage 1 Chip.

It does it with the air off or on. It's definitely not from the A/C. It's just a random fluctuation. Almost feels like it wants to shut off on very rare occasions. It's always done this (or at least since i've been in houston).

2007 4.7L uses an IAC right? Might want to try cleaning the valve to see if that smoothes it out (or just replace it depending how many miles you have)

Long shot but maybe it could be the oil pump? Do you have an oil pressure gauge on your dash? Reason I say oil pump is this past weekend, I was driving my brother in law's chevy truck and at the stop lights, the oil pressure would drop and it would almost stutter out. I put it in Nuetral and rev the motor a bit and it was fine. It didnt' do it constantly but it happened a few times.

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Originally Posted by Aggie07

I only notice the slight fluctuation in RPMs when the AC compressor kicks on and off. Have you tried cleaning the IAC valve to see if that has any affect?

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Sorry, I was not implying that your A/C could be the issue. I was simply stating that is about the only time my RPMs fluctuate, which is normal.

My suggestion was to clean your IAC valve, or like Matt said, get a new one if you have high mileage already.

Loss of oil pressure is due to a loss of RPM, not the other way around. Mechanical pumps depend on engine RPM to pick up the oil.... so if the engine starts to stall for some reason you will lose oil pressure.

Sorry bout that. I saw a bunch of A's and C's together and missed IAC. I've never cleaned one before. Any tips? I take it it's on the throttle body.

yup. easiest thing to do it look up your IAC on a parts website so you can see a picture of it (if you dont know what it looks like)... they're normally very easy to get to.

To clean it you can fill the ports up with carb cleaner/gum cutter/etc... let it sit for ~15 minutes.... dump it out... refill and let it sit for another 5-10 minutes.... then spray the hell out of it.... let it dry and reinstall. Sometimes this work and clears up the issues for a long time, other times it works for just a few days and the symptoms come back (in which case you'd just order a new one).

Roger! I'll get on it this weekend. Thanks guys!

Hey just to add my .02 pennies, had the same problem and it was the throttle position sensors. It's mounted right next to the IAC.

Hey patrick! Thanks. What did you have to do to it? Been a long time.

Yeah it's been awhile, savannah is still the same. There is a new atv park, big nasty atv, that just opened up and there allowing jeeps and trucks there now. It's about 1600 acres. Next time your in town we'll have to check it out.

It was kinda crazy for the longest time I was watching my RPMs flucuate after starting the jeep, but after driving it would be fine. Well as time went on it stated doing it all the time. First start up, stopped in traffic, when ever. I read on the other forum where another member had the same problem, everyone kept saying IAC, but he came back and said it was his throttle positon sensor. Since the throttle position sensor was the cheapest I went with that. I believe it's only held in with 2 torque bits or star bits and electrical connector. It was a pretty easy fix.

I've thought my idle tended to 'wander' a bit myself! I was actually turning a sharp corner today in a heavy rain, and it just about died on me - first time THAT'S ever happened (I mention the sharp turn, because it's a foot off the pedal manuever, and the rainfall, just in case something is getting "moist," that SHOULDN'T)!

I believe the cold idle is set at 800 rpm on the 285; because this is Pittsburgh, and because of my previous experience with other V-8 engines in cold climates, I bumped the cold idle to 950 rpm, which doesn't really do ANYTHING when you're in gear, but it does warm the truck a little faster when you idle it on cold days! ;)

I WILL try cleaning the IAC with a little Sea Foam tomorrow though - before the cold weather settles in again!

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Originally Posted by The_War_Wagon

I've thought my idle tended to 'wander' a bit myself! I was actually turning a sharp corner today in a heavy rain, and it just about died on me - first time THAT'S ever happened (I mention the sharp turn, because it's a foot off the pedal manuever, and the rainfall, just in case something is getting "moist," that SHOULDN'T)!

I believe the cold idle is set at 800 rpm on the 285; because this is Pittsburgh, and because of my previous experience with other V-8 engines in cold climates, I bumped the cold idle to 950 rpm, which doesn't really do ANYTHING when you're in gear, but it does warm the truck a little faster when you idle it on cold days! ;)

I WILL try cleaning the IAC with a little Sea Foam tomorrow though - before the cold weather settles in again!

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It's possible you might have felt the computer reduce the power from the engine I don't know how fast you were turning so just a guess.

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Originally Posted by Sal-XK

It's possible you might have felt the computer reduce the power from the engine I don't know how fast you were turning so just a guess.

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Right turn from a stop light (NO right on red). VERY hard 90 degree turn, so you gotta nudge her out there, and then roll through the turn. You run into quite a FEW of those actually in these ancient boros with narrow streets in Pittsburgh; it makes you see why they sent the CRD's to Europe. As bad as old, large, northeastern cities are, 900 year old ox carts paths in Rome, Athens, Paris, & London HAFTA be 10x worse! :eek:

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Originally Posted by Gulf550

Yeah it's been awhile, savannah is still the same. There is a new atv park, big nasty atv, that just opened up and there allowing jeeps and trucks there now. It's about 1600 acres. Next time your in town we'll have to check it out.

It was kinda crazy for the longest time I was watching my RPMs flucuate after starting the jeep, but after driving it would be fine. Well as time went on it stated doing it all the time. First start up, stopped in traffic, when ever. I read on the other forum where another member had the same problem, everyone kept saying IAC, but he came back and said it was his throttle positon sensor. Since the throttle position sensor was the cheapest I went with that. I believe it's only held in with 2 torque bits or star bits and electrical connector. It was a pretty easy fix.

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I'd love too. I'll also check out that sensor. I miss the old place.

I had a little trouble following war wagon's line there, but (did I say that) I got it now....rough idle, trying to pull through ....Take a look at the spark plug threads, they addressed rough idle. A wider gap or worn plug can add to the idle issue.
I have had problems in the past, but not since I replaced my plugs.

Got new plugs three weeks ago - .040 gap. :) First time I've ever had that issue, and the Jeep wasn't completely cold (I'd driven about a mile & half in heavy stop 'n' go traffic to that point), and it was VERY damp & rainy yesterday. I'm running 89 octane with a Superchips 87 tune, so theres most of the mitigating factors I can think of, for reference.