2004 4.0L Post Engine Rebuild rough idle

[mikeawood]

I bought my 04 4.0L Limited 4x4 used almost a year and a half ago. About 6 months or so ago, I noticed it began to drink coolant. Turned out I was one of the lucky few that had the infamous #6cyl head gasket issue. AWESOME! So into the shop she went for a top end rebuild. My mechanic did a full rebuild including machining the valve seats and cleaning up the heads. Because I wasn't there, I have to take the machine shop's word for it. (the heads looked clean after the rebuild).

Once I got the truck back, the engine was quite a bit stronger so I would probably agree that both heads were indeed gone over. MPG improved slightly from 18 to 19MPG on 33s). So it was worth the rebuild.

The issue I am having is that at idle she runs slightly rough. A/C compressor kicks on and the idle smooths out. Seems like it only does it when at a stop, and only in drive with the A/C off. The amount of vibration doesn't seem to matter whether cold or warm. It doesn't stall and the RPMs don't fluctuate.

In trying to figure this out, I pulled the plugs (they are new) and checked gap. Removed and serviced the throttle body. It was slightly gooey, but nothing that the last 30k miles since it's last service wouldn't produce. Injector cleaner didn't help. Chevron 91 didn't help either. (though she was more peppy and got 20.5MPG)

I've put about 3,800 miles on it since the rebuild. I took it back today to have the mecahnics look at it again. They are stumped and took it over to a local Toyota dealer here in Los Angeles and they didn't have any suggestions either. Basically unless it throws a code, there isn't a good place to start from. I am more curious than frustrated. But I'd like to resolve it.

I am sorta left looking strongly at possibly 2 different things. 1) One or more of the injectors is dirty or damaged or malfunctioning 2) Valve gap spacing is out and needs some adjusting. Both of these thigns require a pretty decent amount of time to diagnose and with the injectors, short of visually inspecting them, I am not sure what else I could do to check them. Valve gap is easy, just time consuming and messy. I figure I'll do a compression test and see if there are any variations and maybe it might just help pinpoint a slightly weak cylinder. I am just not sure if the VVTi will muck up a compression test or not.

Anyone have any other suggestions?

 

[97hb]

I would do a leakdown to make sure everything is nice and dandy after the heads work.

 

[LandRvr Convert]

Mike, I think the rough idle after your rebuild could be just an (albeit irritating) inherent characteristic of way the 4.0 V6 is designed and built.

I know that's probably not the answer you wanted to hear (and maybe I'm wrong), especially when we all put the legendary Toyota quality way up on a pedestal compared to all other automakers.

The reason I think there may be nothing wrong at all, is that I experieced the same rough idle on my brand new 2006 4.0 4x4 the day I drove it off the dealer's lot with about 12miles on the ODO. I still remember starting it (I bought it in June so super cold weather was not an issue) and I remember thinking..........hmmmmmmmm.............it seems like the idle is rough, but hey, it was brand new and there were no warning lights on, so I drove it home and really never brought up this issue with the dealer.

I just accepted it as an inherent design of the 4.0 V6, plus I was enjoying it too much to take it back in for a repair right after I bought it

Long story, short, I sold it after a year and bought a brand new 2007 4x4 but this time with the 4.7L V8, and wow what a difference! No I am not trying to start yet another V6 vs. V8 discussion, but the V8 from the first day with 7 miles on the ODO until now with 115,000 miles has been the smoothest and most quiet engine I have ever driven in any car or suv. Whether at idle or really laying on the gas, it's just smooth as silk, and I think the smooth performance of the 4.7 is an inherent design/performance thing.

Maybe it has to do with harmonic balancers in the engine??

I hope you will get (as you should) many many thousands of trouble-free miles out of your Toyota.

BTW, how many miles total on the truck?

Good luck

 

[BlackWorksInc]

V6 engines tend to be more rough running than V8's, I would ask the dealer or if the shop has a capable scantool to reset the memory on the vehicle. It's mostly for transmission learning, but it couldn't hurt since the engine is different now than it was before in terms of running and such.

 

[03limited2WD]

My 2003 with the 1GR-FE V6 was running rough at 74,000 miles.
I replaced the spark plugs and the PCV valve (12204-31030 - VALVE SUB-ASSY, VENTILATION) Cost me less than 7 bucks for the PCV and I can't even hear or feel my motor running at idle. The old PCV was moving fine, but was coated in what looked like varnish. I Don't know what made more a difference, the plugs or the valve, but the change in engine noise and vibration is like night and day.

 

[lehiguy]

I have 182k on the clock and I cannot tell the difference between idling and not even running, it is perfectly smooth at idle.

 

[mikeawood]

I would do a leakdown to make sure everything is nice and dandy after the heads work.

The mecahnics did it yesterday (they kept it overnight from the previous day), they said it was fine. I didn't ask what the pressure readings were though. But I can just do this myself at home..

 

[mikeawood]

I would be inclined to agree with you about the your V6 running rough, but this one was silky smooth from the day I bought it about 18 months ago. Never idle rough ever, in the cold up in the snow or in Death Valley last summer when it hit 118 outside.

This isn't my first Toyota. My Tacoma was one of those rare few that at 180k miles decided it had enough of my driving it and tossed part of the lower end through the side of the block. We did the engine swap in my garage and the 2nd engine was as smooth as the first.

AFA the balancers... it certainly could be. To me, the roughness feels like an issue with fuel delivery. I still suspect that one of the injectors is either clogged or damaged. I put some 91 in it along with a bottle of techron and at idle, it is a bit smoother. So that would seem to indicate that at least part of the problem is either timing or fuel delivery.

Right now the 4R has 124k miles on it.

FWIW, my Tacoma when I sold it had 262k on it...of course that was the 2nd engine and the 2nd tranny at 259k. It started to nickle and dime me and it was time for it to go. New owner is still driving it in New Mexico now... So, I have realisitic expectations for what to expect I think. @ 124k, this kinda stuff shouldn't be happening...But my luck doesn't seem to agree. hehehe

Mike, I think the rough idle after your rebuild could be just an (albeit irritating) inherent characteristic of way the 4.0 V6 is designed and built.

I know that's probably not the answer you wanted to hear (and maybe I'm wrong), especially when we all put the legendary Toyota quality way up on a pedestal compared to all other automakers.

The reason I think there may be nothing wrong at all, is that I experieced the same rough idle on my brand new 2006 4.0 4x4 the day I drove it off the dealer's lot with about 12miles on the ODO. I still remember starting it (I bought it in June so super cold weather was not an issue) and I remember thinking..........hmmmmmmmm.............it seems like the idle is rough, but hey, it was brand new and there were no warning lights on, so I drove it home and really never brought up this issue with the dealer.

I just accepted it as an inherent design of the 4.0 V6, plus I was enjoying it too much to take it back in for a repair right after I bought it

Long story, short, I sold it after a year and bought a brand new 2007 4x4 but this time with the 4.7L V8, and wow what a difference! No I am not trying to start yet another V6 vs. V8 discussion, but the V8 from the first day with 7 miles on the ODO until now with 115,000 miles has been the smoothest and most quiet engine I have ever driven in any car or suv. Whether at idle or really laying on the gas, it's just smooth as silk, and I think the smooth performance of the 4.7 is an inherent design/performance thing.

Maybe it has to do with harmonic balancers in the engine??

I hope you will get (as you should) many many thousands of trouble-free miles out of your Toyota.

BTW, how many miles total on the truck?

Good luck

 

[mikeawood]

Good suggestion...I will check that out.. The intake was pretty clean (as was the throttle body)...So, I suspect the PCV valve is doing its job. But it's easy enough to replace.

My 2003 with the 1GR-FE V6 was running rough at 74,000 miles.
I replaced the spark plugs and the PCV valve (12204-31030 - VALVE SUB-ASSY, VENTILATION) Cost me less than 7 bucks for the PCV and I can't even hear or feel my motor running at idle. The old PCV was moving fine, but was coated in what looked like varnish. I Don't know what made more a difference, the plugs or the valve, but the change in engine noise and vibration is like night and day.

 

[kao]

Good suggestion...I will check that out.. The intake was pretty clean (as was the throttle body)...So, I suspect the PCV valve is doing its job. But it's easy enough to replace.

Hi, please update status of problem. I feel rough idle on warming and already warmed engine (1200-1300 and 550 (under load) revs respectively). As well as you i met HG failure and replaced HG at 120k miles. At the same time i cleaned throttle body. PCV were changed about 1.5-2 years ago.
Thinking to replace coil tips.

 

[Greydog]

I would ask for the leak down numbers, just to you have a baseline.

Seafoam it, atleast once, maybe twice

Send your injectors to Witchunter or other shops that flow test, you'll get a sheet back with stats. It's like $8 per injector I think.

Could also be a small vacuum leak. Find a shop with a fogger or spray some starter flui near each hose connection or component. Any change in idle or pitch of the running motor means its a leak as it sucks in the vapor.

I think the V6 runs fairly smooth and if you feel this is different behavior vs prior to the rebuild, trust your instincts.

 

[mikeawood]

Hi, please update status of problem. I feel rough idle on warming and already warmed engine (1200-1300 and 550 (under load) revs respectively). As well as you i met HG failure and replaced HG at 120k miles. At the same time i cleaned throttle body. PCV were changed about 1.5-2 years ago.
Thinking to replace coil tips.

I ran down the FSM check list for all the engine sensors (save the knock sensor due to where it is located). All of the sensors were within normal parameters. it doesn't appear to be a vacuum leak as was able to check for that as well. In testing the sensors attached to the vacuum lines, you can pretty much eliminate them pretty quickly.

Throttle Body was clean, but i took it out and gave it a good cleaning anyways.

Since I did the check over a month ago, I can't remember what else I checked.

I didn't replace the PCV Valve yet (mostly just because I haven't gotten over to the dealer to get one).

Given the head work that was done, I am not sure what would be accomplished by adding seafoam to the intake. (I am hesitant in general to add seafoam anyways in general). Maybe the fuel, but the intake should be clean given the machine work that was done. I did add some fuel injector cleaner, but its benefits can be debatable as being effective or not. I didn't notice a change.

For what it is worth, the engine pulls stronger than it did prior to the rebuild so I don't suspect the injectors or ignition. If that was the case, it is likely they would be issues at higher RPMS as well. (though I could just be incorrectly assuming this).

need to get to the dealer to try the $7 fix first... and report back. It has been sitting in the driveway for the most part for the past few months save one camping trip, soI have just been ignoring the problem.

 

[drapaki]

I still remember when I first bought mine (v6). It had something like 5 miles on the odo and hadn't even been dealer prepped yet (white plastic all over, some things still needed to be assembled. awesome!).

anyhow... at idle and in Drive, you couldn't tell the engine was on unless you looked down at the tach. it was glorious!!! I even had someone asked me if my new car had died when we stopped at a light...

If replacing a $7 dollar part brings that back (now 100k miles) I'll be almost as happy as I was that one day long ago. Please let me know!

 

[mikeawood]

Well, I swapped out the PCV valve tonight. And while it isn't back to it's post rebuild smoothness it certainly helped. And for under $7 shipped from back east to SoCal, I am very happy it helped. You can probably check it out by removing it. if you blow into the hose end, it should seal. My existing one did not, the new Toyota replacement one did. FWIW.. It is at the rear part of the drivers side valve cover. You can get at it without pulling anything off with a 19mm deep socket. (You have to pull off the hose).

I only got it up to temp and drove it around the block a bit. It does seem 60-70% better. You still know its in drive and running as you can feel it, but at least the vibration is more smooth so it feels intentional rather than the stuttering I was getting before. Odds are, nobody will notice it but me.

 

[Whitebeauty]

Spark plug gap?Right plugs installed? Also u ever thougt that now more air is coming in n the computer cant correct for it.. I mean u had headwork done on a stock computer. Who does that and not tune for it.

 

[20034RunnerV84x2]

I still remember when I first bought mine (v6). It had something like 5 miles on the odo and hadn't even been dealer prepped yet (white plastic all over, some things still needed to be assembled. awesome!).

anyhow... at idle and in Drive, you couldn't tell the engine was on unless you looked down at the tach. it was glorious!!! I even had someone asked me if my new car had died when we stopped at a light...

If replacing a $7 dollar part brings that back (now 100k miles) I'll be almost as happy as I was that one day long ago. Please let me know!

Just a FYI, I went and got a PCV Valve for my V8 yesterday and the cost ended up at $12.38 OTD.


Sent from my iPhone using Tapatalk 2

 

[mikeawood]

Spark plug gap?Right plugs installed? Also u ever thougt that now more air is coming in n the computer cant correct for it.. I mean u had headwork done on a stock computer. Who does that and not tune for it.

I want to preface this with "I am not trying to argue with you. You might very well be correct. I am open to suggestions beyond what i've mentioned before, but I am only prepared to go to a certain point with figuring this out and then I will just live with it. " FWIW, when its running, its a champ. I have no complaints about street or highway performance. Just the annoyingly un-toyota like idle.

I would assume (perhaps incorrectly) that resurfacing the valve seats and possibly resurfacing the head would only cause a very slight change. In doing so, the stock computer could likely adjust for it. My reasoning being that otherwise we'd all have rough running 4runners as they get older. As valves seats wear and expansion and contraction happen on the head, it changes size as it warms up. (albiet minor). I'd imagine that even though Toyota has strict quality controls that not every engine puts out the same HP due to minor differences between the engines. Small, but likely they are there. I would assume that Toyota put enough forethought into planning for these discrepancies. plus the VVT allows for pretty decent adjustment that are computer controlled as well. So I ruled out having to make adjustments to the computer. Though that is still an option. I suspect someone might have done so previously as it never idled this low before despite the fact that the new idle seems to be right on with the FSM.

As far as "air flow", simple changes in altitude would totally change how it ran, and I've had it up at 8k ft more than a few times and back down to 100ft here at work. I've seen no changes. This still has the stock air box and a clean filter. If swapping to a CAI increases HP and doesn't effect the idle, I don't think there is much that the intake has to do with my issue. So I ruled that out.

Since I have an 2004 v6, there aren't any options really for "tuning". TRD didn't even offer the supercharger for 03-04 because it somehow ended up a red-headed stepchild. I didn't dig too deep into it but basically what I understood is that the VVT is different in the 03-04 than it is in 05+ which makes the S/C not a workable solution. (Similiar story from URD as well, 05+ only) So, when you go to look for computers and such, they just don't mess with my year. Now I could get a piggy back, raise up the idle 100RPMS and have it case closed. But somehow that seems like a workaround and not a solution. I'd like to know why...

It could be something simple like an improperly adjusted valve, a faulty coil pack, bad injector or any number of other things. Since I didn't do the work, I have to trust that the machine shop did things correctly, the mechanics did their job correctly and that it isn't somehing basic.

FWIW, I mentioned about checking the gaps on all the plugs as well as each sensor against the FSM. I did have some sucess with the PCV valve. It was faulty and was a good call by whomever mentioned checking it. But without pulling the valve covers, I am at a place where I am out of additional things to check.

 

[mikeawood]

Just a FYI, I went and got a PCV Valve for my V8 yesterday and the cost ended up at $12.38 OTD.

Did it help? It made a big difference on mine. My other half said its all fixed, but thats not really a good measurement. Our roomie was moving furniture in it and said he could still feel it was idling rough but that it was much better.

Let us know how it goes.

 

[zrgjkfukfhu]

Anyone have any other suggestions?

 

[ebg18t]

Fuel pump? Fuel filter?