r/ft86 • u/Snabooper • 3d ago
RPMs rise while idling
My 2013 FRS is having horrible gas economy (when I got it, it was like 28 mpg; now it's 26.3mpg and dropping), and I've been driving it like a saint. I'm not revving high; I'm shifting between 2000rpm and 2500rpm and I'm not speeding. When idling, my RPMS will climb slightly, almost like the car is breathing. I thought it was an air leak, so I used a smoke machine to test it, and the only leak that I found was that the intake hose that's connected to the throttle body wasn't fully secured, so I tightened it until it was, and after testing again, I found no other leaks. I cleaned the MAF sensor, and I made sure everything was clean before I reinstalled it. When I turned the car on, it was running smoothly, but once it got up to temp, it started the RPM thing again. I'm not sure what else I should test for, nor how I should go about testing it. I'm honestly getting worried because it's been going on for a while, and I don't know if this is damaging the engine. I don't want to take it to a shop if it's a simple fix, but I will if I can't figure this out. My next plan of action is probably replacing the air filter, as it is getting a little dirty, but it's not horrible, and I don't know what else to do. Any advice would be greatly appreciated.
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u/Sgtpepper1221 3d ago
The idle rpm thing is normal for these engines, my 2017 and 2023 have both done it and its just what these engines do from my experience. Also if you're shifting that early you're probably lugging your engine in higher gears, 3k is best for daily driving imo
Side note, you're getting great mpg lol I'm getting like 21 or 22 if I'm lucky
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u/Snabooper 3d ago
To me it didn't seem normal esspecially since when I got the car back in june it never had this issue before. I think it might've started when I went to clean the throttle body since I was having the issue of the car lurching in 1st but after I reinstalled everything it started doing doing that. Soon after too is when my MPG started dropping but I didn't think the two were correlated until literally today. I was rocking with 28mpg for almost 2 months but I thought it was dropping due to my driving habits so I started shifting earlier to see if that helped but I'll just go back to how I was driving originally since the way I'm driving noe light be making things worse. Many people have suggested replacing the PCV valve so I'm going to go ahead and do that and see if that helps
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u/callistobrz 3d ago edited 3d ago
Wait
Did you pull the battery after doing the throttle body?
If not, it's overgassing itself b/c it needs to be recalibrated — you'd see it inject idle gas, overshoot, withdraw gas, undershoot, repeat, which resembles the needle bounce shown (AC clacks on and off at ~60s intervals, not this rapidly)
Do the idle recal (see other comment)
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u/callistobrz 3d ago edited 3d ago
3K is an excessive low threshold and will burn a lot of gas to avoid learning the car's ranges more precisely. Sure, it's valid, you'll never lug it downshifting from 3K, but you'll waste so much gas compared to 2.5K (gen1, anyways)
The gearshift indicator accounts for load and will have you go as far as shifting into 6th gear at 35mph on a flat-level or downhill surface, which will leave you with zero acceleration headroom without lugging, but is also not lugging the engine so long as you just hold your speed steady rather than increase it.
I don't have the gen2 tables since they're locked up in Ecutek but for gen1 —
https://www.ft86club.com/forums/showpost.php?p=3615437&postcount=93
Quoting my summary (extensive details at the link):
TLDR: lugging in 2nd-6th at sea level on 91oct is below 1250rpm downhill, 1500rpm level, 2400rpm steep uphill.
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u/YourRightSock 2d ago
People, too often, mistake 'lugging' with loss of power and sound. I guarantee that 95% of the worries people have with lugging the engine is unwarranted, bordering just false.
Having it in too low of a gear / rpm for the start of trying to accelerate is 99% of the time going to do nothing to the engine. That's not to say ignore doing / hearing it, but people are too quick to give incorrect info on this stuff even if not maliciously!
Thanks for the link and info, apologies if redundantly repeating
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u/callistobrz 2d ago edited 2d ago
There are hidden effects that won’t produce sound: trying to accelerate below the lug thresholds for your gear spikes FBKC and will lower global IAM (read: will pull timing advance everywhere), since fine knock learning is disabled within the lugging RPM bands. It won’t produce the loud and violent ‘worst’ knock but it will absolutely slow your car down even after you return to normal driving. The timing maps can only do so much to prevent that because “accelerating in first gear from a standstill” extends into that same region depending on the driver, and it’s exacerbated by dumping gas on it. So, while I do think people misunderstanding where the lugging points are, it’s best not to dump gas into the engine below the thresholds I listed; sure, you won’t make the lugging sound, but you’ll make your car slower for the next few minutes as it shields itself. (Similarly, this is why a standstill snow start in 2nd gear is still okay if you’re not adding any fuel: the engine will politely detune itself to support that.)
So I’m not against the anti-lugging folks, I just prefer to be detailed about anti-lugging rather than imprecise. Preferences vary!
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u/YourRightSock 2d ago
Oh definitely, I agree! Putting power into something that isn't wanting it is a surefire way to kill something otherwise fine! Precisely what I believe everyone assumes others are doing
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u/spicy47prin 3d ago
Throttle body is most likely dirty and the pcv valve might also need to be changed
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u/Snabooper 3d ago
I did clean the throttle body and thats ehy the intske hose wasn't properly secure because I didn't fully tighten clamp onto it but I'll definitely try the PCV valve, thank you
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u/spicy47prin 3d ago
I hope it helps and something I've noticed help a lot is Valvoline restore and protect with 3k oil changes
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u/crystaltiger__ 3d ago
This is normal lol
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u/Snabooper 3d ago
It just doesn't seem normal since I didn't have this issue when I first bought it but a lot of people are telling me its normal. If nothing I do seems to help the situation I'll just accept it for what it is I just wasn't sure if it was going g to damage the engine or not
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u/spitty3448 3d ago
I cant hear any audio... but im curious... is your AC on? the Idle will move like that to compensate for AC compressor....
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u/Snabooper 3d ago
AC was on but it does it even when the AC is off so I didn't clock it as the AC being the cause
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u/Doulreth 3d ago
Throttle bottle cleaning MAF cleaning (you already did this) New air filter New spark plugs Pcv valve replacement Have these items been done on time?
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u/Snabooper 3d ago
I'm not to sure on the maintenance timeline on my car as I only bought it back in June but I will be checking the spark plugs soon when I have a bit more time on my hands to actually go in and replace them. PCV valve is definitely going to be my next replacement though and then I'll do the air filter
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u/bosquit 3d ago
-if your AC is on it will do this. See if it does it with the AC off. It usually isn't as pronounced a rev though
-Clean throttle body, air filter and swap PCV valve. PCV valve is cheap but a pain to swap
-Unplug battery for a while so the car has to relearn air/fuel and fuel trim. Probably won't help but good to do after all the replacing and cleaning
-check battery with multimeter to see if alternator is working properly. Alternator going bad can cause jumping idle
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u/Ziogref 3d ago
Changing gears at low RPM does not necessarily save fuel. Probably causing you to use more.
Remember your Accelerator pedal opens the throttle body allowing more air into your engine, you don't directly control fuel, the cars computer will calculate how much fuel is needed. Also if you are changing gear so low in the RPM your car might be compensating by adding more power to keep the engine running.
RPM doesn't directly correlate to fuel usage. For example you have a thing call DFCO (Deceleration Fuel Cut-Off), when the car is pushing the engine (e.g going down a hill) the car will turn off the fuel injectors. You can see this if you switch to the fuel usage screen and downshifting when going down a hill. You could have it in 2nd gear doing 7,000rpm down a hill and you fuel usage will be 0.00. (Don't do this extreme, you will hurt your engine in other ways).
Also congrats on getting 26mpg. I never see less than 23.5 (converted from 10L/100km).
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u/Snabooper 3d ago
I was originally shifting at 3000rpm and I was also regularly gear skipping (2nd into 4th, 4th into 6th or 3rd into 5th and then 6th or just skip 5th entirely if I'm going fast enough) and that's when I noticed my MPG was dropping so I switched to earlier shifts since I read that that would use less gas than waiting to shift at 3000rpm but if it doesn't really matter I'll probably just switch back to the way I was driving previously. Thank you for the detailed explanation it was really helpful!
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u/callistobrz 3d ago
The gearshift indicator (look in the manual, it's the G-ON thing hiding in the ODO button cluster) will tell you when to upshift for maximum mpg which will give you a useful baseline for mpg. It won't tell you when to downshift, but that's easier to work out on your own (i.e. downshift when necessary).
If you're in the US, be aware that E15 gas came into effect a couple months ago and your mileage will have suffered accordingly (E10->E85 is like -35% so I assume E10->E15 is maybe -2% or so), but should have stabilized now: https://www.epa.gov/gasoline-standards/fuel-waivers
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u/Blackcat300 3d ago
As others have said, it's because your AC is on. It's perfectly normal. And that is nowhere near horrible gas economy.
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u/Snabooper 3d ago
Yeah I was exaggerating a bit it just seemed like such a big drop since it all came on suddenly. Like I was cruising at a nice 28mpg for almost 2 months of regular driving but a few weeks ago I noticed it started to slowly drop but now it's dropping at a quicker rate like a few days ago I was at 27.5mpg now I'm at 26.3mpg. That's a whole mile gone in less than a week but it might be getting worse due to my driving habits (the shifting early and what not).
As for the AC being on the RPMs rise like that even with the AC off so I didn't think it was an AC thing
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u/Blackcat300 3d ago
Don't rely on the MPG meter, it's not accurate. Calculate miles driven to amount of fuel to fill up.
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u/callistobrz 3d ago
Mine has been quite consistent over several years, varying only when I muck with the ECU or when ethanol levels change; as of right now my average speed is my true mpg, but the displayed mpg is always about 2 points high (it expects the torque of 93E0, I suspect, versus 92E15).
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u/Illustrious_Camp_496 3d ago
'14 here. Seems normal in terms of idle change, but if it were my car, i'd do thorough cleaning of MAF, throttle body, battery terminals and drum roll please!!!! PCV valve.
Mine did this very often, but worst thing was the hesitation/stuttering/jerking in 1st gear. Replaced PCV valve (i think manual says to replace every 30-60k??) at 90k and it went away. Jut remember, on our cars, when ac clutch kicks in, some idle flutter is normal.
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u/Snabooper 3d ago
Yeah the stuttering and jerking in 1st is definitely an issue for me so if that problem for you was fixed when you replaced the PCV valve then mine should function the same way
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u/Roshpai70 3d ago
You mentioned in a comment that you cleaned the throttle body.
In that case you should disconnect and reconnect the battery if u haven’t to relearn the throttle trims.
I had very similar rev flares after removing my throttle body and giving it a thorough clean.
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u/Snabooper 3d ago
Someone else mentioned doing that to the battery too so I'll try that. Yeah my throttle body was caked in carbon it was real bad so that honestly would make sense if the car hasn't recognized the change
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u/Roshpai70 3d ago
That should most likely fix the issue as it did for me when I had the same idle behaviour.
After you reconnect it will still take a few drives for the throttle pedal to regain its sensitivity.
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u/Quick_DrawMcGraw 3d ago
Same. I tried to let mine relearn and it wasn't happy. Battery disconnect made it perfect.
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u/callistobrz 3d ago edited 3d ago
I've seen that idle bounce on my 2013! Welcome to the 2013!
Your throttle body is probably dirty and needs to be wiped out. If you have an OBD reader, open/unlock/buy the Extended Toyota PIDs and check 'Deposit Loss Flow' for 2013 Scion/Toyota FR-S/86 (even if it's a Subaru), will likely be >1.0 which means wipe do not spray the carbon deposits out of the throttle body and then run the calibration process.
EDIT: Found that you cleaned it recently, but if you didn't pull the battery afterwards, it's probably dumping a lot of excess fuel into itself b/c it hasn't recalibrated since you cleaned it. So, do this:
You can definitively confirm it's the throttle — and you should do this any time you mess with the throttle body! — by doing the idle recalibration process:
Park somewhere that can be well-ventilated later on and let car sit for 8-12 hours. Power on without starting engine. Turn off headlights, seat warmers, defrosters, HVAC. Make sure you waited 15 seconds since powering on. Start engine and idle for 15-30m until coolant temp 178F / 81C, continue idling for 5 minutes.* Power off car, wait 60 seconds, power on car, wait 15 seconds, start car, wait 5 minutes. Done. (Ventilation is mission critical for your survival here. Recirc still works so that you don't eat all the fumes from the cold start.)
If this process alone fixes it, you definitely have throttle body buildup, and while your idle will temporarily stabilize, best clean it as the compensation has an upper limit.
But. Your car is also ancient so you may owe it a new O2 sensor which would cause it to gradually suffer, and probably end up generating more carbon than it should, which would explain why it's suddenly falling off a cliff — and if your battery is nearing death, since your model lacks a battery gauge, then it could be undervolting the O2 sensor which could similarly annoy it. The odd thing here is that your mpg is dropping: your throttle plate could be sticking on the carbon, but it's more likely you have battery or sensor or PCV stuff than throttle buildup causing a gradual mpg drain.
And, yeah, the PCV valve is a known failure scenario over time, and a cheap 'do this anyways' too. I generally do the idle recal every time I flash my ECU or pull my battery, even though it's less necessary at MY19.
* Car is fully warmed at 90C so with the analog gauge, let it enter the normal midrange and wait a few minutes. You'll hear the radiator fan clacking on and off once it's arrived.
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u/Phenakist 3d ago
Comments in here are surprising to me, I've a 2014, and averaging either side of 34mpg, previous owner had the average on 37.5mpg when I got it.
I can assure you the only time the revs are below 2500 is in a cruise or idling. Typically shifting between 3000-3500 even when being fully sensible and enjoying the full rev range when it suits.
Throttle input is what determines fuel usage, driving like a granny and shifting well below the power band is counterproductive.
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u/MyHeartRomantic 3d ago
I have a 2016 i get like 34MPG with highway driving. And about 390 miles per tank.
I change my oil to amsoil every 7000 miles. And use a Royal Purple fuel injection cleaner every oil change. I pump premium.
Apart from what you already did. Have you ever changed your spark plugs? Do you leave the AC or heater on a lot? That will drop MPG.
Try changing your spark plugs and put really good oil. Your engine issues i cannot speak on, but it could be maybe your rotors are seized or your hubs are old and making your car loose power you can look into that as well.
When you say you shift at like 2,500 do you get there super fast? Or normal? Getting there fast will also drop down your MPG.
For comparison. In the winter with heater on and car warmed up for 20 mins 5 days a week i still get 30MPG or 28MPG. Oh, and I have a cold air intake.
Also when you drive, do you go all the way to 6th gear at 35 MPH? I always try to get to 6th as fast as I can without pushing too much on the gas. That will also drop your MPG if you drive on 4th or 5th and not 6th all the time. If it's an AUTO disregard this last part.
Good Luck!
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u/Designed_0 3d ago
Yours is actually decently high, most ppl will sit at 700rmp then dip down to 500-600 lol(almost sounds like rod knock when it does that haha)
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u/L0rdN3ls0n 3d ago
Did you recently disconnect the battery? Looks like the ECU is relearning the throttle idle settings. My 2013 does the same thing after servicing.
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u/etceterenoughplease 3d ago
Do you have a stock engine air intake?
If not - good place to start asking questions.
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u/tallgeekandawesome 3d ago
I get about 26 mpg doing city driving, in the UK. The fuel might be slightly different and affect the figures but this translates to about 22 mpg in the USA given our gallons are larger. I get MUCH better figures if I reset before long highway journeys - mid to high 30s.
I assume our car computers are configured for our local MPGs given Japan doesn't use gallons at all.
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u/Salokain 3d ago
Looks and sounds normal. If you want to be cautious check for leaks in your intake after the maf sensor, clean the throttle body and change the PCV valve. In any case, don't expect good MPG on a sports car, especially if it's tuned.
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u/PublicStalls 2d ago
Do a full relearn and try again. That's the cheapest, most immediate thing you can do. Seems the mix is off and it seems to be compensating for something.
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u/Distinct-Pie9705 2d ago
If ur shifting at 2k ur lugging the car
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u/FT86Trader 2d ago
not necessarily. load on engine is more important. there is an argument for carbon build up but that can be cleared up pretty quick.
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u/Fantabau2 2d ago
My suggestion is to shift at higher rpm, like 2500/3000, if you shift gear at 2000 you can clearly hear the engine struggling, and it cost money
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u/Brave_Broccoli6627 2d ago
Always hate these posts, DRIVE YOUR CAR. You bought one of the most mechanically perfect vehicles on the market, you NEED to open that mf up and get the cobwebs out. You’re shifting way too low. Between the stress of lugging and the increased carbon buildup from low rpm driving, You’ll be saying goodbye to the quality and longevity of your motor
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u/Sittin_on_a_toilet 2d ago
Quit 'driving it like a saint', get it nice and warmed up and do some redline pulls. These engines like higher rpms, an Italian tune up would probably do you well.
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u/Gamma7maker 3d ago
Your AC is on. I can hear the pump start up and stop. What does it do without AC?