What am i doing wrong?
 

How do you deal with "clogging up" your car from hypermiling?
I have noticed that regardless of the car i do some mediocre hypermiling with, it always becomes sluggish after a while.
Then i have to "floor it" for a while and everything is back to normal again. Does not make sense to hypermile just to lose all my results by flooring it once a week :D

I do a lot of coasting in neutral and DFCO.
Quick accelerations and steady speed after that when on the faster roads.
I do all my "hypermiling" after engine is warmed up.

Maybe you would benefit from hotter spark plugs. Are they all carboned up?

Maybe the ECU is learning your driving style? Also possible that your car becomes less responsive when fully warm, sometimes emissions programming comes into play more the longer you drive.

I'm with Ecky on this one. I'll bet it is the Ecu learning your driving style and dumbing down throttle inputs. My dad's 2008 G35 would do this, it would also hold gears longer when I drove it.

I'm with Ecky and Daschicken. Lots of ECU and transmission control systems learn their drivers' behavior anymore, and tailor their own behavior to match. Without digging into whether your car is so equipped, I'm still willing to make the assumption that either or both are behaving they way their programming assumes you want them to behave.

Flooring it once in a while just gives the computer a Gibbs slap, in this case not entirely deserved.

I would wager you're losing some of your gains by doing so, but not all. And then there's this: if you know that gains have been made, why are you cancelling them out? You're aware of the car's behavior but let's face it, neither of your vehicles are especially quick so your default reaction in an emergency would never be to floor it, but stomp and steer out of trouble. Why floor it at all?

Thanks for the tips, everyone.
Elhigh, with our current cars at the moment, the avensis gets in a "mood" that every little uphill requires downshifting to 4th gear, and generally the whole driving feel of the car becomes bad. (press the gas pedal, car thinks for a second or two, then something finally happens)
When driven normally, with a firm acceleration now and then the car performs good. (not meaning fast :D)

And just for clearance, i am not one those guys who blast their way out of trouble. And i do not overtake easily. Only tractors and other slower things.
But i want my car to operate properly when i need some power out of it.

Gasoline engines have always had a tendency to "carbon up" when not driven hard. This is a natural result of the engine not getting "hot" enough to "burn off" the fuel deposits left after combustion. Kind of like clogged arteries to us couch potatoes. In my case, I used to notice it more when I drove overpowered V8s that loafed a lot more than the four-cylinders I've been driving in the last couple of decades.

Some folks like to use what is sometimes called the "Italian Tuneup" to mitigate this mechanical artery clogging, which consists simply of accelerating hard and raising the RPMs enough to clear some of the residual carbon from the engine. I "floor" my Mazda3 once in a while when entering a 70 or 75 mph Interstate. I sometimes can see a bit of grey or darker smoke come from the exhaust when I do this, proving that something different is happening.

I can't prove the Italians know what they are doing, but I "think" the technique helps keep the spark plugs and valves a little cleaner than they otherwise would be. The use of good quality gasoline which contain the proper cleaning additives also helps, I "think."

I don't notice any decrease in MPGs when I do this occasionally, and it does assure me that the car will respond appropriately in emergencies when the dozens of little ponies under the hood are called upon to get me out of trouble even if it is at the expense of a few more oats at dinnertime.

Engineering Explained has a video which explores some of the evidence behind the Italian tune-up. I believe his conclusion was (if I remember correctly) that the numbers don't really support it working, but I'd have to watch it again.

https://youtu.be/5C9Ie4BcYew

This is exactly what i meant, thank you.
I have heard somewhere that driving with ethanol would clean off them build-ups even better? :confused:

If there is buildup, it would be over a period of tens or hundreds of thousands of miles. This is not something you'd notice likely even year to year.

I hope that's true, because a 10% ethanol mix is all I can conveniently get around here. And even though straight gasoline is available in a couple of places, its extra expense doesn't seem to justify its extra MPG potential nor the efforts it takes to find and go get it.

Thanks go to our influenced politicians for this contrived state of affairs.

Not sure about the effectiveness of the "Italian tune-up", but in light aircraft still fitted with piston engines it's not unusual to lean the mixture for a while in order to increase the temperature in order to eliminate lead fouling around the spark plugs' electrodes. But anyway, at least in a port-injection engine, I wouldn't expect too much carbon buildup around the valve seats, even though in newer cars with direct injection the fine particulate matter emissions have increased to Diesel-like levels.

I have a similar problem, my car runs like dogsh*t sometimes after hypermiling, needs a good thrash.

Normal driving (keeping it loaded at low rpm) it clogs up something (i'm not sure what.. EGR?) and thrashing the car helps.

Normal thrashing can help sure, but also in a low gear (2nd gear 40-50mph on my Jazz) high RPMs i find transitioning from lowest throttle state (that's not DFCO) to max throttle state, over and over to help. I think this makes the ECU move the EGR a lot and can solve the sticky valve somewhat.

My throttle pedal is definitely adapted to the driver, it becomes more relaxed when i drive it (changing mapping mid drive sometimes which is annoying, my rev matched downshifts can be messed up by this a little). But when the car is running bad, it feels like it's always in both too high and too low a gear. (hard to explain really).

I cleaned my EGR and it was very carboned up, car runs nice, all the time.
Recommend resetting your ECU afterwards though (disconnect battery for a few mins or so)
And it'll take a little bit of time for all the values to be learnt back, but it's amazing how much better my car is now.

Throttle pedal is instant! No more running on exhaust gases when it shouldn't be, also mpg has improved too..!

EGRs and throttle bodies seem to require cleaning i think, i need to do my throttle body next, but the EGR has helped a lot.

Did you also take a look at the crankcase venting (PCV)?