Hey guys,
For over a year now my 4Runner usually idles real rough for the first 5-10 seconds after starting it up. It only happens after the engine has sat for at least an hour. If I stop somewhere for under an hour, it'll idle great when I start it back up. It been happening more and more frequently - it does it almost every morning now.

When I say it idles rough, I mean it shakes the truck and the RPMs kinda go up and down like it can't decide if it wants to fast idle at 1000 or 1400. It will either go away on it's own in 5 or 10 sec, or I can tap the gas a couple times and it will smooth out. The engine sounds a little rough too (almost like a small exhaust leak) and then it just snaps out of it and starts purring beautifully.

After it does it's idle thing, the truck runs awesome. I have lots of power, engine sounds great, no issues at all. Last June I put in a new front O2 sensor and it seemed to fix the idle thing for about a month. June was also abnormally cold this year where I live. I'm not sure if it was the O2 sensor that made the difference, the cold weather, or neither, but it's back now with a vengeance.

Here's what I've done recently:
-Cleaned MAF
-Cleaned throtte body/IAC & new gaskets
-Cleaned PCV valve
-Coolant temp. sensor (just looked dirty and old)
-Bank 1 knock sensor (threw code)
-O2 sensor (old 1 had 185K on it so I replaced it)
-Timing belt/w.p. (2 weeks ago)
-Plugs/wires/coil boots (6 months ago)

I also replaced the starter a little over a year ago (around the same time I first noticed the idle issue). Any ideas/help would be appreciated.

 

Mine did this and I ended up having a blown headgasket and cracked head. After sitting for awhile coolant would leak into the cylinders and make it run rough untill the coolant would burn up, then it ran great. I would do a compression test to be sure.

 

Did a comp. test and a leak down about 2 months ago and found no problems. Plugs all looked good. Consistent coolant level. Oil is nice.

 

Sounds like fuel injectors are leaking...all of the fuel leaks into the cylinder. The engine runs rough until it can burn all the excess fuel off. Toyotas are notorious for having leaky injectors. Easiest way to check it is to install a fuel pressure gauge see if it bleeds off..alot of people deal with it as injectors can be pricey x 6.. hope it helps or gives you something else to check.

 

Thanks for the tip. I'll hook up a gauge and see if the pressure drops. If that's the problem, I'll probably just roll w/ it for a while - unless it gets way worse. Any risk of doing damage to the engine if I don't fix it right away?

 

Ive never seen any long term damage from it. You might go thru plugs faster, as it might foul them more. I really dont know though. I have never heard any horror stories of running an engine like that. Maybe someone with some experiance can give us some insight. Let us know what happens though.

 

Thanks digitalracer, I'll post the results when I do the fuel pressure test.

 

Injector leak down can on rare cases cause hydrolock. If you bump the starter and it loads down stop and wait a while for it to seep through the valves or pull the plugs. I've only seen this twice so its a rare thing but can happen with injector leak down.

 

mm mine did that (88 22re), low confused idle until a blip cleared it up,Like yours after warm and had been shut off. I did have a bit of white milky ikk on the inside of my oil cap. Anyway i solved that bye breaking a spark plug in #4, Head off to the shop, Dang cracked head. Alls good now runs good, idles a little high, could be the to cold thermostat, anyway keep us posted on how it goes.

 

Thanks guys. I hope it's not a cracked head or a leaking head gasket, but it seems like all the clues on mine point towards an injector as opposed to a head thing since I'm not losing any coolant at all and both the oil and the coolant look nice and clean.

Thanks for the tip. Wouldn't want to lock the engine up. I worked at a marina for years and saw lots of hydrolocked boats. Usually that happens when the engine dies and as it's slowing down, the wake catches up with the rear end and swamps the motor right through the exhaust! Bad stuff, I'll be sure listen to the starter more closely.

 

I just thought of this, but there is a hose coming off the rear Driver's side of the engine that connects to my air flow tube, right before the throttle body. It looks like this hose would normally go through an EGR valve before it hits the TB, but my truck doesn't have an EGR (I don't think). Anyways, if I pull this hose off, there usually a little bit of dirty gas that drips out. Seems like this would support a leaky injector right? - like it's not burning off all the extra fuel at start up and it's recirculating the unused crap back through the airflow? Just a guess, but seems logical.

 

I would look at the injectors since your compression is good. 3rd gens do have a problem with leaky injectors.

 

out of curiosity, where exactly did the head(s) crack and how did you go about fixing it? new/used?...

 

UPDATE:
So I checked the fuel pressure and no drop, so it doesn't look like it's a leaky injector after all. I'm leaning towards a HG now. I have also kept a close eye on my coolant since this thread and it seems I have lost a little (overflow used to be at full when hot, now it's about 1" lower after a couple of weeks).

I had good compression when I tested it (180-195 in each cyl.), but the engine was still warm when I did it. I'm thinking once the engine gets going and starts heating, the leak seals up and thats why my engine runs fine after 10 seconds.?? I'm going to do a comp. test in the morning when its cold and see if it's any different.

I've searched around for threads on re-torquing the head gaskets and found a lot of info on the 3.0, not so much on the 3.4. I have read that people sometimes have them re-torqued shortly after they are replaced. Mine were done about 3 1/2 years ago and I was never told to bring it back and re-torque/check them so I didn't. I'm thinking I might try this if I confirm it is a HG leak before I go and replace them. So my question is, can the HGs on my engine even be re-torqued or no?

 

bump...
Does anyone know if I can re-torque the HGs? I ask because they are a specific torque spec then you turn 90 deg. and then another 90 deg., so not sure what the final torque is. Has anyone tried to re-torque their's 1st, before replacing the HGs? Just want to buy some time.

 

I was under the impression that the head bolts on the 3.4 where "torque to yield". So "re-torquing them is a not recommended.

 

I have heard that too, but I have to admit, I don't know what that means. I guess it means "no".

 

yea mine dose the same thing just a rough idle for about 1 min my injectors are fine and the head isnt cracked

 

Rupert, how long has yours been doing that? Is it a 3.4L too?

 

mine has been doing it for a cuple of months it started when i replaced a cracked rubber boot on the intake it dosent run as rich as it did when there was a little crack in the boot going to the air box
its a 3.0