Idle gets slightly rough when in gear

[AaronHartwell]

Hey guys,

I have a 1996 4Runner that I just bought. It has 140K miles and has been meticulously cared for with all schedeuled maintenance being completed by the dealership.

While idle is super glass smooth I noticed tonight that when I shift into drive the idle gets slightly rough. It's fairly minor but the OCD in me can't let it go.

Any ideas? Because the idle in neutral or park is absolutely perfect and I've just done plugs, wires, air filter, synthetic oil change, new radiator, I suspect it's something related to transmission and not engine.

Thoughts??

 

[02-Sport]

My 01 does the same thing, It's not bad but not as smooth as it is in park. When you put in drive the idle drops.
I've been thinking about adjusting the idle up just a little bit to where it idles smooth in drive. Not sure if it would idle to high in park after adjusting?

 

[ekin]

If can find much bigger place

 

[AaronHartwell]

Increasing the idle speed might smooth it out but I'm guessing that would just be masking the root cause.

I played around with it tonight and discovered one thing that might or might not be helpful in diagnosing.

If I came to a stop at an intersection I would get the rough idle while my foot was on the brake. If I shifted in to neutral (N) it smoothed out. If I shifted the truck into drive (D) and didn't move the car forward it stayed smooth!

Odd...

 

[AaronHartwell]

o2 sensor - after a bit of research this evening it sounds like bad TPS (throttle position sensor) or dirty MAF (mass air flow sensor) could be the problem.

Aaron

 

[AaronHartwell]

To keep chiming in on my own thread for those of you who are following along, if any...

After a bit more research it sounds like bad engine and transmission mounts can also cause the behavior I'm seeing. :fishing:

 

[Baja Runner]

Idle gets rough? Do you notice if the RPM's are actually fluctuating differently? Do you think its strictly under load?

I would personally skip O2 sensor, MAF and TPS for the moment....

While I think what you are describing is actually somewhat "normal" for these trucks, I understand what your saying is annoying. Have you had someone shift through the gears while you're underneath the truck or got your head under the hood? I'd try doing that to see if anything shifts.

For months I had a weird vibration only in Drive, and when I was stopped. As soon as I took off, no vibration, and if I was in Park or Neutral, no vibe. I instantly thought transmission. Guess what it was? Exhaust pipe got bent when offroading and I had no idea.

Not saying that is your problem, but I think these trucks are really hearty, and after owning 3, I've had close to NO problems with any of them. I would check the easy stuff first. I wish I could help you out further...

 

[kman55]

If it helps at all mine drops a bit in rpm's when put in drive from park. Same deal, it's not rough necessarily, just not as smooth as park. Alot of things I have driven do this, I just assume its normal. Mine hasn't acted up in five years, not saying yours couldn't be a problem. Just trying to relieve some worries.

 

[Alabamaguy]

Mine does this as well. I read in another thread that it can be caused by a clogged or faulty fuel injector, however unless it's throwing a CEL I wouldn't worry about it.

 

[kman55]

Mine does this as well. I read in another thread that it can be caused by a clogged or faulty fuel injector, however unless it's throwing a CEL I wouldn't worry about it.

Damn I fuel injector would suck, but I hear ya there buddy! If it ain't broke, don't fix it.

 

[AaronHartwell]

Thanks guys!

It sounds like what I'm experience isn't all that unsual and taking a chill pill might be the right remedy.

The RPMs do fluxuate. When I first start the truck the RPMs spike up to 2000 where they sit for probably 5 seconds and then it seems to settle in around 700 at which point the idle is glass smooth.

I've noticed that when I come to a stop and the idle gets a little rough the RPMs have dropped down closer to 500. I'm guessing this is because the transmission / driveshaft is putting some load on the engine when stopped? Sort of like partially letting out the clutch while holding the brake if a manual transmission?

Aaron

 

[Alabamaguy]

Thanks guys!

It sounds like what I'm experience isn't all that unsual and taking a chill pill might be the right remedy.

The RPMs do fluxuate. When I first start the truck the RPMs spike up to 2000 where they sit for probably 5 seconds and then it seems to settle in around 700 at which point the idle is glass smooth.

I've noticed that when I come to a stop and the idle gets a little rough the RPMs have dropped down closer to 500. I'm guessing this is because the transmission / driveshaft is putting some load on the engine when stopped? Sort of like partially letting out the clutch while holding the brake if a manual transmission?

Aaron

Not exactly, the initial high idle is the engine in closed loop mode where it's warming up. In this mode it operates off a set of pre-determined perameters and this high idle is completely normal. Once out of this mode, into what's known as open-loop, it should idle around 600-750 rmp depending on the specific application.

(this is hiw it's been in every other application I've been familiar with, anyway. Should be similar but this is my first Toyota EFI setup)

 

[AaronHartwell]

I think that all makes sense Alabama. So are you saying that what I'm seeing is normal (2000 RPM at start-up, quickly dropping down to around 750-700, and then 500 when at a light)?

 

[02SE]

Not exactly, the initial high idle is the engine in closed loop mode where it's warming up. In this mode it operates off a set of pre-determined perameters and this high idle is completely normal. Once out of this mode, into what's known as open-loop, it should idle around 600-750 rmp depending on the specific application.

(this is hiw it's been in every other application I've been familiar with, anyway. Should be similar but this is my first Toyota EFI setup)

FWIW, that's backwards. It's in open-loop while warming up, and closed-loop when warm. The exception would be when given full-throttle while warm, then it will revert to open loop, and run at a richer than stoichiometric A/F ratio as determined by preset parameters in the ECU.

OP, without being in your truck, it's hard to say how 'rough' the idle is in gear, and whether it is normal. It will be slightly rougher when in gear at a stop vs in park or neutral, simply because there's a load on the engine bringing the RPM down a bit.

 

[AaronHartwell]

OP, without being in your truck, it's hard to say how 'rough' the idle is in gear, and whether it is normal. It will be slightly rougher when in gear at a stop vs in park or neutral, simply because there's a load on the engine bringing the RPM down a bit.

O2SE - Ok. It doesn't feel like it's going to die or anything that significant but I would say that it goes from being a smooth idle in neutral to what I would call a slightly rough idle when stopped at an intersection.

 

[jpmoco10]

Hey guys,

I have a 1996 4Runner that I just bought. It has 140K miles and has been meticulously cared for with all schedeuled maintenance being completed by the dealership.

While idle is super glass smooth I noticed tonight that when I shift into drive the idle gets slightly rough. It's fairly minor but the OCD in me can't let it go.

Any ideas? Because the idle in neutral or park is absolutely perfect and I've just done plugs, wires, air filter, synthetic oil change, new radiator, I suspect it's something related to transmission and not engine.

Thoughts??

Aaron - I realize your original post was five (ish) years ago but I was wondering if you ever figured out what was causing the loud vibration? I have a 2006 Toyota 4Runner (100k, meticulously cared for) and it recently starting doing the exact same thing.

I have always noticed a difference in the idle speeds while at lights and I did a little research on this and it is my understanding that a 4Runner will adjust its idle depending on many variables such as: air, temp, fuel, etc. and that it might also “vibrate” or change its natural frequency when it detects a load, such as an air compressor or heater activating. I’ve heard that the car will run at a reduced RPM for a limited time and then the ECU will bring the RPMs back up to normal idle speed.

This has never concerned me until the last month or so when that idle noise became louder. There is zero vibration when the car is in park or neutral. It is only when I am in drive and at a complete stop. As soon as I accelerate, it goes away. To further complicate things, I can't say that it happens 100% of the time, but it does happen about 80% of the time now and my OCD has my mind racing.

Any advice/update would be much appreciated!