I went down to the field to do some pattern work. Just wanted to do 5 or 6 touch and go's for no reason other than it was really nice outside. Plane (172) I was flying just came out of annual. I do my preflight, everything is good. I start taxiing. I notice that it seems like I'm having to use more brake pressure than usual to keep the plane at the speed I want. Don't really think much of it, been a while since I flew that plane. Just not used to it I guess.
Get down to the end and do my runup. When I get to the 'idle' part of the checklist, I notice that it's idling around 950rpm. Well, checklist says "ensure engine idles smoothly above 575rpm". It was, so, I moved on.
Call and get cleared into the pattern. First T&G, I feel like my pitch attitude isn't right. But my speed was right on the numbers. I'm thinking maybe the wind shifted. I was landing 21 and wind was reported 200@8. I was floating and floating and floating. Check, yes, throttle is all the way to idle. Stall warning horn isn't coming on. I touch down, but I know I'm still pretty fast. 45kts or so. I bring up the flaps and off I go again.
I'm thinking "Wow, I have 200+ landings in this plane. I don't remember ever floating that much. Can't believe I'm so rusty. I must have just carried too much speed into the flare. Glad I came out to practice landings today!"
2nd time around, I make my short final about 62kts, just a little slower. STILL floating. I touched down, but the plane just felt really light. What the hell is wrong with me?? Raised the flaps and off I went again.
3rd time I decided that I just wasn't 'right' to be flying today, so I called for a full stop. I'm following a Hawker. He lands beyond the fixed distance markers, so I come in high and position to land beyond his point. I'm STILL floating really long. I'm in ground effect, but the damn plane just won't quit flying. I glance at the RPM and it's at about 1000rpm. Suddenly everything clicked. Something's wrong here. I don't know what's causing it, but I realized I was floating so much because "idle" was 500rpm too high.
I was now halfway down the runway and still floating. I don't know if it was the right thing to do. But I was just a foot off the runway, and I didn't want to keep flying this thing. I don't know if what's wrong is going to get worse or what. So, I pulled the mixture and let the prop windmill for just a bit until I slowed enough to touch down. Once I was under control and firmly on the ground (we're talking seconds here) I put the mixture back in.
Engine still running at near 1000rpm. Took a lot of brake pressure to keep the plane slow all the way back in. For reference, if you look at the taxi diagram for KSDL, I was landing 21. My aim point on the last landing was just beyond A13. After getting it on the ground and slowing it up, the first runway exit I was able to make was A5. Just shy of the fixed distance markers for runway 3. 8000'+ runway and I used more than half of it landing a 172.
I should have realized something wasn't right when I was having to use so much brake pressure to keep the plane slow at idle when taxiing. I should have realize that close to 1000rpm at idle was way too high. I should have realized after my first T&G that I had too much RPM at idle.
Just sort of a kick in the nuts that I ignored so many little warning signs. I know this isn't a big deal in the scheme of things, it's just a good reminder to myself that if I'm asking myself "is this normal???" I need to really put some more thought into it rather than just brushing it off.

"Fresh out of mx" can be either really good or really bad

I believe statistically it's when most incidents/accidents happen.

Sounds like you've got a maintenance tech that either can't read or is too lazy to follow the prescribed maintenance procedure. That should've been easily caught in the post maintenance run-up.

At least you didn't force it on the runway and risk losing it on roll-out.

When a plane comes out of maintenance, I'm extra-vigilant for shit to happen.

That was why I pulled the mixture.  I knew I had plenty of runway remaining.  I knew I could have forced it down (I already basically did twice - the first 2 landings were much closer to go-arounds than they were T&G, even though the wheels did sorta touch the ground) but I didn't feel safe doing so.  

I didn't want to go around again.  I didn't really understand the WHY of what was going on.  Is this a symptom of something worse about to happen to the engine?  I didn't know for sure, but I knew for sure I could land it with no power in the distance remaining.

Was that the best choice?  I still don't know.  I know it was the right choice for me at the time.  If I had to do it again, I might have tried landing without flaps first, but I think that would just have made me even faster.

I was just talking about the 172 with my brother. He is a pilot in a king air, and a DC12 but still teaches in a 172 to a rich dentist. They were out flying and the dentist wanted to have some fun and see what my brother could do. He said even he was surprised when he landed. Came to a full stop and took off again and had only reached the 1000' mark. The fact that you floated half a 8000' runway was a big indication something was amiss. Granted not a life threatening one. But reminds you to take a second look at everything when flying. And remember. No matter what is happening. Fly the plane.

Not sure what the POH says for your airplane, but for most planes I've flown, pulling the mixture is what you do for a stuck throttle.  

As an aside, if you ever do multiengine training, you'll see that one way to simulate a failed engine is to pull the mixture back halfway.  It allows your instructor to cover the mixture handles so you can't see which engine he or she pulled.

You can also bleed the flaps away in the flare. Don't take away all of them, just from 40 (or 30 if that's your norm) to 20. A lot of people are uncomfortable with this and the FAA would never condone it but it's easy to do in a 172 and makes for a very smooth, nose high landing. I wouldn't make it your normal routine to land like that but knowing you can do it can help you out in a pinch. Would've worked great in your scenario.

So what do you do in a soft field landing? Similar power setting.

Not really.  Soft field is maybe 100 or so extra RPM that you can take out as needed.  This was enough extra RPM that I probably could have flown in ground effect forever.  

I talked to the FBO today to find out if I was crazy or what. They had a CFI check it out (mechanics are out until Monday). He started it up and started messing with the throttle. He couldn't get it under 1000rpm on the ground. They looked under the cowling and found throttle assembly at the engine was loose and about to fall off. Makes me feel a little more confident that I made the right decision. I could have given it full power, had the linkage completely fail, and then I would have HAD to make power off landing with no way to go around.

Or, I could have ended up trying to go around and having the assembly fail at 1500rpm and not be able to climb. An off airport landing near my field is a very dicey proposition.

Overall, I feel pretty solid about my decision.

The mech that signed it off needs a little wall-to-wall counseling.

In any event, what you did worked, you didn't panic or lose your cool and that's what counts.

Good job and thank you for bringing that to our attention. If I had to rent for whatever reason, I don't think I would have noticed this either without this topic. Most checklists have run-up defined as:

Fuel Pump - ON
Mixture - RICH
Prop ...
Mags ...
Engine to IDLE. Check smooth running.

I always thought that "check idle" was to make sure the engine didn't quit at idle and not to verify that it was sufficiently low. I've heard of worse things happening when an engine gets pulled to idle, like a reversible propeller going full reverse.

I was taught that "engine to idle" was to make sure the engine RPMs would actually drop like they were supposed to. A failure to drop RPMs was an immediately cancelled flight.

The problem with that is, unless you're a mechanic. what IS idle?

OP's a smart fella, mechanically inclined, and didn't recognize an 'odd' idle until late in the flight.

To combat this, I submit your PERSONAL checklist (excluding 121/135 guys, you DO have one for each plane you fly, yes?) should have the "normal" idle setting.
Let's face reality in that each plane will have a different number, but it should NOT be a gross variance from the POH.

I should have noticed it.  I did notice it, but I didn't put any weight on it.  If it had been 1500rpm I would have known something was off, but 900-1000?  It just never even crossed my mind that it would be an issue on landing.  The CFI I trained with is adding that to his curriculum.  It's just never really come up before I guess, lol.  

I'm glad it was me flying the plane and not the me from 5 months ago when I was just starting to solo.  

To make myself feel better, I flew my wife to KSEZ for dinner.

Short final, Runway 3 KSEZ.  

Nonsense, you've got all that real estate that the 101 gives you!

Great job catching what could have been a much worse situation. I've called a few flights before, one of which was on my commercial check ride, and it's not easy sometimes. At the end of the day though, you got to go home, and that's what matters!

I was taking off on 21.  It's a little more sporty.  

You should have gone around.     You almost painted yourself into that corner you hear about.

Learn to never trust mechanics.   Every time you fly an airplane just out of MX, your face should wear a permanent

How so?  5000' of runway remaining.  Plane is in ground effect less than 2 feet off the ground.  What benefit would there have been to going around?

And knowing what I know now, going around could have been disastrous.

I guess 5000' is still enough.  Didn't see that part. You indicated you were already landing long.

The main thing to take away from this, is if something seems off; Park it.

As you've seen, the High Idle RPM might not be too serious on it's own, but it is indicating a much more serious, potentially life threatening problem.    

This is a common thing.   Always listen to your inner voice, when it's telling you something is just a little "off".

Yes, I was long, but it's an 8300' runway.  On a shorter field, I would have gone around and hoped for the best.  I had more runway left than most of the airports I land at have runway.  

The second part was really what I learned from this.  If something's not normal, I need to stop and take some time to figure out what it is, and what the consequences could be.

  glad it worked out for you

Got my license and scheduled a nice 700nm flight. Detoured due to snow and landed a 182 in 45G50 winds...was like a helicopter on base-final. Checked all airports around and this was the least wind around for 80nm

I instruct for one of the larger flight schools, our checklists say max 700 rpm and min 500 during the idle check in the Cessna (172M,R, and S)

Thunderbird is pretty wide

The comment to not trust the mechanic is partially true. When I perform maintenance or inspection, i either get another mechanic to QA using the discrepancy list prior to closing up the airplane or if there is no one else, i take a break and without distraction go over it again myself. I have out of necessity grabbed a trusted pilot occasionally. I tell all pilots the most thorough preflight should be the first one out of maintenance. Like Ronald Reagan said: Trust but verify. 
I'm glad you recognized the severity of the situation, I know pilots that would have ignored it and kept going.