Fluctuating idle 2.7 manual

Recently bought a 2009 2.7l 5-speed manual with 200k miles. The truck was running rough and lacking power during acceleration. I replaced the spark plugs (which were in bad shape), cleaned both the throttle body and MAF sensor, and "reset" the ECM by way of a lengthy battery disconnect. The truck runs much better now with no problems with acceleration. However, when it has reached operating temp, there is an intermittent fluctuating idle. What I mean by this is that when I am at a stop, with the truck in neutral, the engine will fluctuate from 750 down to 500 RPMs and back up to 750. Much like what is experienced when an AC compressor kicks on however, this fluctuation occurs with and without the AC on, and does not occur during all idle occasions. I have checked for a vacuum leak and have not been able to find one. Could it possibly be an injector or ignition coil issue? Can the resistance be measured on these to determine their efficiency? Or could it be something else that I am overlooking?

I've searched the forums a lot for what the problem may be and I've read that these 4 cylinders can have a "rough idle", but as this is my first Taco, and I'm not sure if what I'm feeling is normal or if I have a problem. Thanks for any insight into what may be going on with my truck.

 

How long have you been driving around since your battery was disconnected? I ask because the trucks idle low after losing power as the truck "re-learns" it's operating specs and sometimes it can take a couple of days before it gets back to normal.

If it has been awhile since you re-connected the battery, then it could be your ignition coils. this website explained the testing procedure much better than I could: https://www.yourmechanic.com/article/how-to-test-a-spark-plug-ignition-coil-by-eduardo-ruelas.

 

It's been about 2 weeks of driving, however, I have not gone through a full tank of gas yet (I have a short commute to work). I've read that it can take a while to "re-learn", but I was unsure of the actual amount of time needed.

Thanks for the website, I'll try and hunt down the correct ohms readings for my ignition coils.

 

Check for vacuum leaks.

 

I have already checked for vacuum leaks by using the carb cleaner approach. I sprayed the length of each line and where they terminate while listening for a change in engine speed. No changes in engine speed.

 

Check to see how much build-up is behind the throttle blade.

 

Thanks. When I cleaned the throttle body, I removed it from the engine and thoroughly sprayed both sides of the throttle blade and walls of the throttle body. I scrubbed it as well with a sponge soaked in carb cleaner to remove some of the more stubborn build-up. When I was finished, I did not notice any carbon on any interior surface.

 

More than likely the idle air control is still a little dirty.. I would pull the throttle body back off and clean it again, and when your done take compressed air to it and blow it dry (through all passage ways inside to).

 

Thanks. I'm assuming that the idle air control is in an inaccessible space within the throttle body assembly, correct? If I am remembering correctly, I sprayed cleaner into the passages and allowed it to air dry (I lacked access to compressed air). I can retry this evening cleaning the assembly with the aide of compressed air.

Outside of a potentially still dirty throttle body assembly what stands out as a possible cause for the fluctuating idle?

 

Yeah it's almost impossible to access the IAC while the throttle body is still attached to the intake, and even still a pain in the ass to get the screws out of it when it's off, that's why I would just take it off clean it again and use the compressed air to dry it off and maybe blow more crap out of it.

I really can't think of anything else other than dirty injectors that would cause a fluctuating idle.

 

Thanks. I removed the throttle body from the intake to clean it previously. In doing so, I did not notice anyway to access the internals of the throttle body short of removing the rivets that are associated with the electronic actuator assembly on the side of the throttle body. Did I miss the screws then?

I tried SeaFoam in the gas tank to clean the injectors. Adding a "cleaner" to the fuel is the only cleaning alternative short of removing and having them professionally cleaned, correct?

 

By the way I don't know what brand throttle body/carb cleaner your using, but Napa sells a 3M brand throttle body cleaner that's better than the CRC cleaner..

 

Yeah the seafoam in the tank should help you out on the injectors, but I really doubt it's the injectors.. Toyota probably has changed the throttle body's on the 2nd gen to not being able to take anything apart on them now since their throttle by wire and wants you to buy an entire throttle body when something on it fails..

 

bad cat

 

The idle on my 2.7 has fluctuated for a long time. Other than being a little annoying, I haven't bothered with it but have been contemplating cleaning the throttle body recently. I keep forgetting to buy cleaner when I stop at the part store. I'm due for a spark plug change soon, so I'll try to do it then since I've got to take off all the junk going from the airbox to the throttle body anyways.

It's takes 100-200 miles for the ECU to really re-learn everything. My daily commute is 90+ miles round-trip, and it takes a couple of days to get back to normal. When I first startup after having the ECU unhooked, I usually have to give it a little gas to keep it from stalling, and sometimes it wants to stall at stop lights until it's figured out what it's doing again.

 

Took the throttle body off the and cleaned it (again). Noticed that there are no internal ports to clean out, just the throttle blade.

I've done some more driving, enough for the ECU to re-learn everything. Still have the fluctuating idle, does not occur at every instance, but it is there, and makes the truck shake when it drops down to 500 RPMs. What would you suggest is the next course of action?

Why would a bad cat cause a rough idle? There is nothing shaking around in the catalytic converter.

 

Just one of the parts that commonly go bad with these model years. It doesn't always rattle depending on how the honeycomb is degrading. It could just be partially clogged with fine debris.

 

I really doubt a bad cat going to cause just a rough idle, you would have other issues with drive ability other than just a rough idle.. Do you have any codes or have a way to check for any codes? Could be a issue with the throttle pedal sensor or throttle body itself.. How many miles are on the truck?

 

I do not have a CEL on and I don't have a way of scanning. Is there a way to scan the ECU through the OBDII and a jumper wire (I did this when the ABS light was able to pinpoint which sensor had gone bad)? Or should I just go to an auto store?

The truck has 200k miles. How would I go about checking the functionality of the throttle position sensor?

 

If it were me, I would take it into the Toyota dealer and pay them to diagnose the problem cause they have the scan tools/equipment to do it a lot faster and cheaper than trying to throw parts at it and hope you get the right part replaced.. Or you can try and get the auto parts store to see if they would hook up the scan tool just to see if there are any codes.

The only way I know of checking the throttle position sensor( accelerator pedal sensor) or throttle body is having the dealer check it out with their scan tool, the auto parts store scanner won't cut it as the dealer's scan tool is going to give real time results/issue's..

Is it just a rough idle or are you having other issue's with it as well? Like poor acceleration, missing,loss of power, ect..?