Rough idle when in drive at a stop

2008 Tacoma, 4 cyl 2.7, 130,000 miles. When stopping in drive, engine runs fine but it will start to slowly (about 10 seconds) slow down and idles rough, RPMs drop - slightly, does not stall, but I know something is not right. This happens only when in drive, and the AC off, if I turn on the AC, engine RPMs pick up and it smooths out. After spending hours researching on this forum and not finding a possible solution, am reaching out. What I have read throughout this forum, points to IAC valve, but this year Tacoma does not have one. The other possible fix would be cleaning the throttle body? Tried so far: 2 bottles of injector cleaner (Royal Purple) cleaned the MAF sensor. New plugs at 120,000. I want to avoid the stealership and last auto shop I took it to ( for a different problem) hosed me, so any suggestions?

 

Sounds very very similar to what I am experiencing with my truck. Need an answer!!

 

Any codes?

If you haven't cleaned TB than it can't hurt.

 

Disconnect the battery, clean the throttle body, reconnect and let it idle up to operatung temperature to relearn the idle. I bet that will fix your issue.

 

Engine light is not on, I don't have access to scanner to check for soft fault or bad indications. Watching a YouTube video on cleaning throttle body; (on a toyota 6 cyl) the guy says need to take the throttle body off to clean both sides and it's necessary to use a new gasket. Is this accurate?

 

I had the same problem with mine (V6 though). I cleaned the throttle body and MAF Sensor and it fixed it....idles smooth now.
I took my throttle body off to clean both sides and I did NOT use a new gasket and it was fine.

Cleaning those two things also made the truck much more responsive!

 

It's common for toyotas to idle low like that, probably fine. Notice how it's never actually stalled?

you can try cleaning the throttle body but don't expect any big changes

I wouldn't worry about it

 

Could it be a torque converter ?

 

Got an 09 2.7 4 speed auto here. It's all vibey at idle in drive, less so out of drive. 55k miles on it now.
i've replaced the air filter, cleaned the tb, gone over the vacuum lines and verified no leaks. recently replaced the cats and muffler with Walker, along with the rubber insulators. (no code, but the reader showed the system was going) new o2 sensors, exhaust gaskets and hardware. Engine n tranny mounts replaced with new OEM ones. Spark plugs are doing alright. compression's okayish (think they all read 170s)
Driveshaft doesn't vibrate. just the engine. I think it's just goopy in there from periods of sitting and the weird pcv system toyota uses.

if i ever get time i'll pull the head n timing chain cover, square all that away. I tell yuh man, if I got into a new truck at the dealership and it idled crummy/vibrated and the salesman said "well, it's a truck" i'm sure we'd both have a good laugh.

 

Took the throttle body off today, cleaned both sides, (was not that bad at all) reinstalled, did the relearn idle procedure, no change. Almost anyone else would think nothing is wrong, but I am the original owner and I know it's not right. Will accept it as is, until I find a competent mechanic with a scanner. If I do I stumble on the solution I will post, thanks to all for the suggestions.

 

Make sure your terminals on the battery are nice and shiny clean, go the extra and put some dielectric grease on them.
As stated earlier in thread, make sure your Throttle Body + MAF is clean, and air filter.
Lock-out your Serpentine belt and check your AC pulley(all points of contact, really) and belt tensioner for weird noises, or the belt not being centered on the pulley/s.
Also, understand the AC compressor is a big draw, and you will feel it engage. It shouldn't drag/bog the system though, so take care of those easy steps and let us know.

 

What is weird about the Toyota PCV System?

Intake sucks on the valve cover through the PCV Check valve.

 

Apologies, the PCV system isn't weird, but the EGR system is. I'm accustomed to seeing a big ol' electrically operated EGR valve, and the 2.7 at least doesn't have one. Has some kind of valve setup on the exhaust manifold and since I don't understand it I'm suspicious.

 

Neither of the 2nd gen Tacoma engines have an EGR valve, EGR (Exhaust Gas Recirculation) is accomplished by varying cam timing as it is on most VVT engines.
The valves you see on the exhaust manifold are for the Secondary Air Injection System which is only there to assist catalytic converter function during cold start rich conditions.

 

Any update to this? My truck has been having some of the same symptoms

 

I went ahead and redid the timing and balance shaft chains. Also swapped the throttle body for an ebay junkyard one ($35). It had a snappier throttle plate once I cleaned it up, so I installed it. Throttle is snappy now -- responds quick. but the fault is still there. I'm 100% convinced that whatever the fix is, it's in or on the cylinder head. Either with the valve train or the head gasket.

I think the 2.7 is just going to be sensitive to this kind of issue because of how the engine is mounted: just sitting on rubber blocks vs. other mounting styles like being hung/suspended from rubber insulators, or a hybrid setup.

At some point I'll take the head off..

Oh, I've also got ignition coils just waiting to go in, so there's the tiniest sliver of hope there, but I'm not holding my breath at all. -- I sprang for premium ones too, that boast their insulation against radio interference. (think they were Hitachi) But since the vibration gets better when the gas is pressed, I'm not really suspecting Radio Frequency to be an issue.

Thanks for the reminder. i'll update when the coils don't work

 

My 2.7 was vibrating the steering wheel at low idle also, delayed throttle response on accelleration, felt sluggish uphill,( as others said, almost acceptable as normal )
Then I got a few events of violent shaking on cold start with a CEL code for CYL 1 misfire that would go away on restart ( but no popping as typical with a misfire)
I am not a believer at all in Fuel Additives, I thought of them as just overpriced "Snake Oil" and laughed at the price of the BG fuel system cleaner ( $30 for 11 oz can ) but a service advisor I trust at a dealer recommended it on diagnostic guess of spark jumping or sticky injectors ( said BG fuel system cleaneris the only one hes found that works and swore it wont hurt the CATs)
I cringed and ran a can of BG snake oil through it and the cold start shake hasn't come back , but the best part is that the steering wheel vibe at idle is gone, it accellerates smoother with no delay and even seems to have a bit more power climbing grades.
I really do not want to suggest anyone waste money on the snake oil remedy but .....it actually worked in my case, I am shocked

 

@Dustrider my dude, you sold me by acknowledging that it's snake oil. I'd throw any number of new to me $30 gambles at this thing before dealing with the freakin head gasket. You know, after I shake the moths and bird bones out of my wallet.

 

Trolling by wondering if any of the above issues are caused by the wrong spark plug gap?
Skimming through the thread, I haven't seen it mentioned, though a case or two had mentioned changing plugs.

 

It's a hail mary to throw the BG at it but
Before doing any motor work, I would check compression and if in spec ( especially not two adjacent cylinders) and not losing coolant there is no point (?)
and a compression reading is a somewhat relative measurement due to a few factors and a compression leakdown test tells more about valve sealing but is more involved, sometimes can hear a leak at a valve or adjacent cylinder(head gasket) with a stethescope or piece of tubing to the ear, and discover a shim and bucket valve adjustment problem holding a valve open or burnt valve ( however if one of these needs a valve adjustment , it probaably needs a new valve too because it has a stick shift and got overrevved )
...and I would hook up a vacuum gauge to see if the needle is sitting fairly smooth at idle, if the needle flails it could be an intake gasket or intake leak somewhere (?)
also in play could be fuel pressure , checked in line with an actual gauge , maybe a jammed regulator or check valve (? )
I was just wondering about the evap charcoal canister on these , does it have one ? where is it ? I have heard of tuning issues caused by an overfull / soaked charcoal evap canister or even gas cap not venting causing low fuel pressure or fuel leakdown after engine stop (?)

as a side note if it gets to that , also be aware that the head bolts on these are intended as ONE TIME USE ONLY , you need to buy new head bolts or the gasket job will only last another 10-50,000 miles, don't let anyone tell you different unless you want to learn the hard way or like high stakes gambling