Fluctuating idle 2.7 manual

So, still have this fluctuating idle. About 3 weeks ago the CEL came on and the code was P0420. Replaced the O2 sensors figuring that if I was going to have to replace the cat I would replace the sensors as well. Well the sensors didn't fix the problem, so I took it to the dealer, told them about the code and the fluctuating idle, they hooked it up and monitored the sensors pre and post catalytic converter. Told me the catalytic converter is failing, so I decided to replace the catalytic converter. No codes, but still have an idle that fluctuates between 700-500rpms and the truck shakes when it reaches these low rpms.

The truck is a manual 2.7l with 200k miles. I replaced some parts (plugs and coils) because of the mileage and not knowing when they were changed last; the old plugs were in rough shape.

Things that I've replaced:
Oil and oil filter
NGK iridium spark plugs
Denso coils
Denso A/F sensor
Denso O2 sensor
All vacuum hoses

Things I've cleaned:
MAF sensor
Throttle body

Could it be that the throttle body is going bad? Is this something only the dealer can diagnose?

 

Modern vehicles tend to cycle the AC compressor even when the AC is not turned on. Keeps the components from seizing up from lack of use. Have you checked to see if the AC clutch is kicking in when the RPM's rise or drop?

 

I've not checked that. I'm familiar with the rise and drop in rpm's from an AC compressor and the fluctuation I have would seem to occur at a greater frequency. It goes from 700 to 500 to 700 to 500 within seconds and continues this pattern. I would imagine an AC compressor kicking on would cause a momentary drop in rpms, but this would stabilize until the compressor kicks off?

 

Hm. Within seconds seems like it may be something else; usually the compressor will kick on for 10-30 seconds and then back off, depending on the level of freon in the system. The only time I've seen them cycle rapidly like that was when they were nearly out of freon

 

Yeah, I'm familiar with the rapid cycle of an AC compressor when it is low on freon. This seems to me to be even quicker, I also don't hear the audible click when outside the vehicle when the compressor clutch would engage or disengage.

My biggest fear is that this idle problem is what led to the catalytic converter going bad and that if I can't get it fixed, I will end up destroying the new converter.

 

Have you tried and explored anything out of the engine bay, fuel pump? Clogged fuel filter maybe?

 

Resurrecting this oldish thread because I still have a fluctuating idle. What I mean by this is that the idle fluctuates from about 700 to 500rpms cyclically when the engine is warm and when it reaches the low rpms the engine stumbles enough to shake the entire truck. It is a 2.7l manual transmission 4x4 regular cab with 207k miles.

I recently took the truck to the dealership for them to diagnose. They told me it could be a bad TB because there was a recall, but couldn't pinpoint that as the culprit and told me to wait until whatever was causing the problem to get worse, i.e. the throttle body going out completely. They quoted me $2k to replace the throttle body (because I was outside of the allotted mileage for free replacement). Instead of waiting for the problem to get worse and paying the dealership, I bought a new TB and replaced it myself only to have the problem remain. Prior to this, the truck had a CEL for the catalytic converter and I had that and the accompanying sensors replaced.

Things I have done to try and fix this problem:
New throttle body
New catalytic convertor
New A/F and O2 sensor
OEM spark plugs
OEM coils
Cleaned MAF sensor
All new vacuum hoses
New PCV valve

I have decent gas mileage (~22mpg on the highway) and the truck does not have any performance problems while running, hence I don't believe it to be a problem with getting fuel to the engine (fuel pump, fuel filter, injectors).

I'm hesitant to take it back to the dealership, but I don't want this problem to lead to me having to replace anything that isn't broken. Any ideas on what could cause this problem? Thanks.

 

Dis you ever find the fix to this problem? I'm having a similar issue.

Forgot to mention mine is the same engine but an 06 with less miles.

 

Nope. Still have the fluctuating idle. Seems to have increased in it's occurrence as well, almost every time the truck is at idle.

 

mine does it too. 05 tacoma. 122,000mi. very annoying.

 

Mine does it too. 65k miles 2010, also 5spd 4x4. Not enough to shake the truck and it never stalls so I'm not worried about it.

The cat should have been replaced under recall. Mine was last year.
Do you have any info on the throttle body recall? I haven't heard of that at all

 

That was only 2010-15 trucks anything older was not included. i loved that recall made a lot of money off that one.

 

It's really hard to even start to give help for this without proper data logs. i would want to see multiple logs at idle and just see what every sensor in the engine data list is doing. But i'll through one out there did you replace the PCV when you did the plugs they are plastics and tend to fail and can cause some weird shit to happen.

 

Which one?

 

The F0U campain 2.7 trucks.

 

? I meant which recall for the 2.7
Cat or Throttle Body? I'm looking for details on the throttle body recall that was mention and want to see if my 2010 Taco is affected

 

Yeah, I replaced the PCV valve and was careful in doing so.

How do you think I should go about approaching the dealer in this situation? Last time I was there, I had to ask them to run a diagnosis to check out the fluctuating idle.

As for the Throttle Body recall, I'd not heard of it before, it just something that was mentioned to me by the representative in the shop last time I was there.

 

Honestly i work for the dealer so my advice is this. Go in and ask to test drive with the tech and duplicate your concern multiple times during the road test. If you can duplicate a concern easy and numerous times any problem can be fixed eventually. Driveabliity concerns are super hard to diag and takes time so understand it make take a few hours.

 

I can try the test drive approach, thanks. However, last time I was there, it wasn't that the truck idle wasn't fluctuating while they were problem solving, the technician experienced the problem. They also had the truck for 8hrs or so.

I forgot to mention that both him and I could get the fluctuating idle to alleviate slightly by just turning on the AC. What about increasing the load or RPMs would cause the fluctuations to minimize?

When I have some free time again, I will take it back to the dealer.

 

Update.

Took the Tacoma to the dealer and test drove it with them. The idle would not fluctuate with them in the vehicle, of course. While driving home I noticed that they had turned off the heat, and the head lights which I usually leave on... Turned those both on and low and behold, the fluctuating idle began again. So, I thought it may be a problem with the charging system and I took the truck to the local parts store and had them check the alternator and battery, both passed their tests... Removed the grounds associated with the battery and the alternator and cleaned the contacts to ensure a good connection. After that, I confirmed that the idle fluctuations occur when the accessories are being used.

Could it still be a problem with the charging/electrical system?