FIXED!.. I think ;) Need help chasing down sudden rough idle!

Hello Tacoma people. I'll jump right into it. This is about my:
'01 PreRunner V6 Automatic 133,100 miles. No CEL currently showing.

I began to occasionally feel a little bit of a engine stumble every once in a while, but had smooth idle so I went through a long process of performing various maintenance jobs on the truck in my effort to get rid of the stumble, but I now have a rough idle that I can't figure out.

Here's what I did and found out during the process in order:

Just edited: I forgot to mention that I also changed the fuel filter aside from everything below in my quest to resolve the roughness:

1. Ran two bottles back to back of fuel injector cleaner. No difference.

2. Pulled Throttle body. Very dirty - cleaned thoroughly with TB spray cleaner. Removed IAC. Very gunked/dirty - also cleaned every nook and cranny with TB spray cleaner. Reinstalled both parts to torque with new gaskets.

3. Adjusted throttle & trans cable at Throttle body to remove bit of slack.

====>Result from TB and IAC cleaning and cable adjustment - Truck ran smooooth and now was much more accelerator responsive from the cable adjustment. Felt amazing, just like new.....then...
Stumble came back half a day later. The maintenance/chasing continued:

4. Pulled spark plugs. All were normal looking except No. 4. The boot on that plug was semi loose so it pulled out almost effortlessly. The exterior of the boot was filthy with black carbon. I went to take out the plug and it too was very very loose. I pulled it out after only a couple of short turns of the ratchet. The entire plug was blackened from what obviously was blow out from the chamber. This had to be the cause of the stumble.

5. Installed new NGK plugs - Dual Electrode

$7 BKR5EKB11 NGK Spark Plug Stock # 3967

BKR5EKB11 and New NGK TE66 4412 plug wires. I didn't use anti seize because NGK calls for no anti seize to be used on these plugs.

6. NGK plugs were all factory gapped at .021 at each electrode to center . This threw me off, so I read up online. One NGK user called NGK and NGK said .021 on these plugs is correct - DO NOT GAP, they function at the .044 gap the factory requires.

7. Truck ran kinda rough right away. Pulled plugs after a few days. All looks ok other than No. 4 didn't look like it had burning as much as the other plugs when you compared them all together.

8. I wasn't convinced on the NGK's so I decided to switch them out for dealer plugs.

9. Installed new dealer

$20 Denso K16TR11 Spark Plugs, Pack of 4

Denso K16TR11 Pre Gapped plugs with a bit of anti seize on each. All gaps were the same.

10. Truck ran kinda rough... right away again.

11. I thought, damn, faulty NGK plug wires maybe?? ...$$ more money spent on dealer real deal wires.

12. So now I had bought and installed new Toyota Dealer Denso Pre Gapped plugs and new dealer plug wires. The previous wires before the new NGK's were the original ones (I've owned the truck since new) and the previous plugs were 40,000 mile old single electrode Autolite Platinums - ran fine with that set up. The plugs all show .025 gap on each side of electrodes - different from the NGK's .021. I haven't seen any explanation why factory states the gap should be .044, yet the correct pre gapped dealer plugs are .025 each side. We're not supposed to set/correct these plugs.

13. I used a bit of anti seize one each thread and some dielectric grease on upper plug body.

14. Truck ran rough at idle. Read a lot online and found anti seize is unnecessary on modern silver thread plugs and die grease might mess you up too . Wound up pulling out plugs, cleaning all anti seize and dielectric grease off and cleaned off plug chamber threads. Cleaned out all plug chamber threads with a plug thread chaser multiple times. Wiped off each time until they were dry and free of showing anti seize.

15. Reinstalled to torque all plugs, although some plugs - especially No. 4, only tighten a couple of 1/4 ratchet turns before it reaches torque (all plugs tightened after hand set down to seat first).

16. Reinstalled plug wires in correct order.

17. Idle improved. Drove it for a couple days - still has irritating semi rough idle, especially stopped in Drive at red lights, compared to how it ran a few days earlier - before I pulled the old plugs and wires.

18. Removed plugs again. Again I noticed No. 4 wasn't showing as much burn as the rest of the plugs. It actually looked pretty unused/new with little burn on tips of electrodes. Cleaned out plug chamber seats. Turned engine couple of times with plugs removed.

19. Checked ignition coils by pulling each out individually while in idle. Engine stumbled badly after pulling out ignition coils individually. Also, partially pulled each ign. coil out to listen - you could hear spark ticking on each in chamber.

20. Vacuum leaks - Checked as many air hoses for cracking at connections. Cut off small amounts on any that showed cracking and re-connected.

21. Put everything back together... Still have irritating rough idle. Not severe, just irritating. I really want it to feel like it did a few days ago right after I cleaned the TB and IAC. The truck almost felt brand new for about half a day after the TB/IAC cleaning.

22. One other thing I notice is a bit of condensation coming out of exhaust now even in very warm weather.

23. Also (maybe a big clue) the truck runs smoother in colder (night time) weather, and it's now typical rough idle in warm/hot weather. Heat seems to aggravate the idle issue. Some sort of expansion happening?

I also did run the truck on the freeway at 40-60 mph spurts in 2nd gear to blow out carbon.

Any clues as to what I should look for now? I went from factory non recommended single electrode Autolite Platinum plugs (which ran really well for years) to now the factory recommended dual electrode plugs. Is the truck not liking the correct plugs maybe? Ignition coils seem ok.

 

Hmmm, wow. Maybe no#4 has an issue with plug hole threads, seems to me theres gotta be a code stored, & gotta make sure all sensors are good like MAF,etc;

 

I thought the same so I plugged in my code reader to see if anything happened to come up. Nothing did but I still wonder if it should be throwing a code. About 3 months ago, it threw a Catalytic Converter code which could have been many things. I ran a bottle of Cataclean, cleaned my K&N filter, reset the EFI fuse/battery cables and cleaned my MAF sensor thoroughly with MAF spray. CEL went away, truck ran well for about 300 miles then same code came back. Truck still felt fine (until now after replacing plugs/wires), gas mileage wasn't any worse so I erased the code and it hasn't come back.

I did run the thread chaser 14mm tool into plug #4 extra times. I did get some resistance from the carbon build up on the threads at first then finally kept wiping off the tool - repeated until clean. Chamber #4 is suspicious.

 

Might have a crack around that plug hole, you mentioned about finding soot around plug threads I think...

 

Do those engines need valves adjusted around the milage you're at? My Honda Fit with 100k needed one when it started stalling out when cold. Mechanic thought it might be the throttle body so I cleaned that out and it ran better, but did not fix the issue. Not sure about your engine.

 

Yeah lots of soot all in that chamber, on boot and all over the spark plug. That plug came loose somehow at some point (recently probably) and was allowing burned/unburned gas to escape up through the threads and out into the plug chamber. Not ruling out a crack, but more than likely, the plug barely sitting in it's hole very loosely (and boot loose off of plug) was the cause of the soot and stumble.

 

Hmmm suspicious.

 

Not sure, but don't think that is the problem since this occurred immediately after changing plugs and wires.

 

Yeah but it still doesn't thread right correct ?

 

Yeah it almost sounded like it's cross threaded and could maybe not be holding compression?

 

I mean if you chased threads it should thread easily

 

Cool. Good to know.

 

Well, it does. It's just that the no.4 plug and a couple of others ratchet tighten to torque very quickly after hand tightening/seating (about 1/8 to 1/4 turn passed hand tightness. Whereas I believe 3 other plugs tighten to torque in about half a ratchet turn after hand tightening/seating. Apparently, this isn't uncommon from all I've read online.

 

Can you get it compression tested? Would it be worth it?

 

Probably wouldn't be a bad idea. I can get a loaner compression tester from a local auto parts place.

 

It threads in nice, straight and easy like the rest, just tightens to torque extremely quickly after hand seating down to where it bottoms out by hand.

 

Hmmmmm. Aggravating. Other things to test that could cause intermittent/changing behavior senstitive to temps and run times:

When you cleaned the TB and IAC, did you install new gaskets? The TB gasket is single-use only crush gasket, could have an air leak there.

Other thoughts
Throttle Position Sensor. Apparently they have a tendency to fail but I am not sure how it manifests itself. I believe there is an FSM test procedure for resistance and correct operation.
EGR valve
PCV valve

 

Yes, verry irritating, especially because I'm pretty decent at amateur mechanical work and rarely ask for help, but I am stumped and need help in this case (pride is hit a little lol). Yes, TB and IAC gaskets were new. TB gasket was the OEM metal type. IAC was the rubber OEM type. I thought of TPS. Not sure how to go about testing it either. I do have an ohm reader, just not very versed in using it. The EGR also crossed my mind. I never dealt with mine. There's some confusion with EGR's as it seem our California trucks have one but not all US trucks do. It looks like my EGR (if that's what I've seen) is at the rear of the Throttle Body, just next to the TPS. PCV valve is semi new, and small valve inside moves freely. As a matter of fact, in chasing this, last night I remove and replace with new PCV valve grommet (p.i.t.a. by the way). I also cut off a bit of the end of the vacuum PCV line where it connects to nipple at the manifold just to tighten it's loose fitting. No difference.

 

Well blarg. Yeah, I just replaced the PCV in mine mainly because the gommet fit was loose. Those damn grommets are a pain. I just put the new valve in the old gromment, and it was much tighter, so that solved that...

I just attached the FSM inspection procedure for the TB /TSP

EDIT: attachment corrected for V6.

 

Yeah, I had a tough time pushing the PCV valve into the new grommet, finally got it in by pushing down on it with pliers opened up wide, placed the pliers at the base "shoulder" of the valve and pushed down. Went in quick after figuring that out.

Thanks for the inspection procedure. I'll use it!