Low & rough idle with intermittent stalling and no throttle response when warm

Interesting sperrunner. With the engine warm idle speed in park(or neutral) should be 750rpm +/- 50, correct? If the TPS wasn't advanced enough wouldn't I have a low and rough idle at all times?

 

Yeah it should be around 750 when warm. Cold starts it will jump up pretty high so maybe the sensor is off enough to allow it run fine when cold because the ecu is giving it gas but once it warms up and starts to back off it kills the car because now your rpm is to low.
This is just a wild guess

Could probably be caused by a dirty or faulty sensor.

 

I have the drive by wire system; I was under the impression that the ECU handles idle speed? Regardless, I am at 730-740+/- when warm and in park. RPMs drop to around 600-650 when in gear, which I hear is normal.

 

When you remove your throttle body there is a small plate on top with four screws, remove that and you should see several small holes. Clean that out if it's dirty. This is part of what regulates the idle on our drive by wire trucks.

 

Thanks Thunderone. I had no idea under that plate could be cleaned. I will do that tomorrow.
I drove yesterday and just for the hell of it I hooked up my Bluetooth OBD2 scanner and fired up my DashCommand app. It did begin to idle roughly when leaving work so I checked for codes and finally 1 then 2 showed up as pending codes. P0171 and P0305. I’m suspecting I have a vacuum or intake leak somewhere past the MAF??? I know unmetered air can cause misfires just curious as to why it’s only one cylinder??

 

Hmm.. that I'm not sure of. You could try spraying some carb cleaner or starting fluid near hoses while idling to see if the idle picks up.. this will help narrow down the location of a possible vacuum leak. Only other thing I can think of would be a bad injector on that cylinder, or a bad gasket on the intake manifold.

 

So took my truck to the shop yesterday. They found no intake leaks anywhere and said hoses were all good. Checked pcv valve and it was good. They hooked it up to their Toyota scanner and said all the fuel trims were good and found no other issues. Unfortunately, it never stumbled or acted up for them on their test drive or while it was idling for quite a long time. Their only suspicion is the injector on cylinder #5 that originally through a pending code for me. They recommended a stout fuel treatment dose of 3 x 6oz bottles of Lucas and told me to drive through that tank of gas and add some more Lucas to the following tank to see if possibly clears up. Should I wait a few weeks and see what happens or assume the injector is going bad and swap it out? If I replace it, should I go ahead and do them all?

 

if you only know one is bad, then replace just the one. They are usually quite expensive. That being said, you could try to run some cleaners through there to see if it'll help, but it may only be a temporary fix.

$25 BG44k BG 44K Fuel System Cleaner Power Enhancer 11oz.

BG44k is a good strong cleaner if you want to go that route.

 

Any further info raptor510? I got a p0171 code the other day and the truck is running rough. Cuts out at first when you floor it. If you ease into throttle it revs normal. Doing a live data test on my scanner my long fuel trim was -14.9 and short was 1.6. From what I have been reading, high positive long fuel trim points to vacuum leak. Haven't found anything stating what it would be if its high negative. I am guessing weak fuel pump with my numbers. I checked for leaks and cleaned/checked Maf and it's good. You said you had your fuel pressure lines checked? Any idea how they do it? I have read nobody sees a schrader valve on these 3.4l.

 

Hey djohn24! Been super busy and forgot to close out this thread.
In the end I wound up replacing the fuel injector in cylinder 5 and have not had an issue since then.
My mechanic tested the fuel pressure by opening the crossover pipe in between both fuel rails. There is no test connection on the 3.4l. My fuel pressure was great but it was a brief pending code that pointed me directly to cylinder 5 and after I checked the spark plug and compression the only other option was the injector.

 

Happy to hear! Thanks Raptor!

 

FWIW I had a very similar problem with my 2004 3.4L Tacoma. Took it to the dealer. They did an "upper fuel service" whatever that was and it helped for a while then the problem re-emerged. Replace the MAF, plugs, air fliter and fuel filter, no joy. It was miserable driving the truck. I was running out of easy/cheap parts to replace. This went on for almost two years. I figured it was some kind of fuel pressure problem thing and then just last week it thru a P0031 code. Sensor 1 bank 1 O2 sensor. I replaced the sensor with a Denso and it runs like a new truck. Apparently O2 sensors can go bad enough to make the vehicle run badly, but not produce a code and it can do this for a long time. Hope this helps somebody.