2000 Toyota 4Runner 5vzfe V6 4x4 - Low Idle

I have a 2000 Toyota 4runner 5vzfe V6 4x4 with a low idle. Runs great except for at idle, no codes.

When coming to a stop from cruising the engine bogs down to 450 ish rpms and then settles out at 600, which is lower than spec. Spec idle is 750 +- 50.

New plugs, wires, boots
New Maf
New o2 sensors
Iac is clean and working, it starts up and idles correct until it hits 175° F then it instantly kicks down to 600 rpm, i assume thats when it enters closed loop.

Cold compression is also very good all the way around.

Any help would be greatly appreciated. I do have a scope, but havent tested anything yet.

Thanks!

Are you able to watch scan data during the warmup and the low idle symptom? We'd be especially interested in fuel trims and idle motor control %.

I would like to know the cause of this too. I have a Toyota with the same problem, idle drops down very low when hot. Fine upon restart, which I assume is the same as yours? I had read that when removing the IAC you should mark its position first, could try an idle relearn? there's a process for it. Video should be on youtube. Hope you find a solution dude!

How many miles are on the car? Check crank and cam signals see if it fluctuates or drops out. Possible signal issue or timing chain and guides is what im thinking

Here is some info from the scanner, ignore the p0340, and the trans code. The p0340 was a bad pin on the ecu. I have fixed that and is no longer an issue. The trans code is there because this is a swap into a manual trans 4runner, defeating the codes with a reistor and the sensors makes that code go away, so no issue there either.

Every now and then you can hear the engine blip up and it will suddenly rise to 630 rpms or so before it studders back down. Now and then you can hear a blip blip blip, sounds just like a small missfire.

Cam and crank signals look good, all injector signals look good, all have pintle movement. Secondary ignition signals looked good from what i could tell. At idle it was kindof hard to see since the wave kept jumping back and forth horizontally at idle, but i could get it to display a somewhat steady signal at anything other than at idle. I could also only test one side of each cop since there are only 3 wires for 2,4, and 6. 1,3, and 5 are cops.

The blip up in rpms tells me something is definitely wrong, and when it blips up suddenly, whatever the problem is must intermittently go away for a split second.

Thanks for your replies!

There isnt anything to mark when removing the iac, only when you remove the backplate with the weird spring inside.

Ive tried the idle relearn, from what i know it only works on camrys and the 2.4 L 4runners, click the key on 3 times and then start. Tried that numerous times with no results.

Unknown miles, this motor was pulled from a wrecked 4runner. Has great compression and drives like a dream other than the idle issue. All timing is good, the marks all like up, ive checked it twice, never messed with the cams under the cover either but since compression is good i assume the valve timing is fine. Belt, tensioner, and idlers are all in good shape.

I just checked iac waveforms and the ecu does send a square wave on both ground sides of the iac. So i assume that that those waveforms are good. I guess the next step would be to check hot resistance of the iac. I did at one point install a chinese iac and the idle ended up high, so i do think my iac may be bad, even though it bench tests good.

Did you ever find out what was wrong with it?

kamiwolf0893 wrote: Did you ever find out what was wrong with it?

Unfortunately not yet. Ive checked all my wiring at least 5 times, all thats good as far as visual inspection/function. Ive read the crank waveforms and cam waveforms, both look normal, i have not looked at them at the same time though, but since i have good compression all the way around im confident that my valve timing is correct, ive verified that its correct visually as well.

I did notice the other night that that it seems like it might have something to do with fuel trims. The ecu was fresh, no stored information, it was just sitting idling and the idle blipped while i was watching the fuel trims, and at that moment was when the long term fuel trim adjusted more negative.

Long term fuel trim tends to hang out at -7.6 ish while idling and 0 at 2k rpms. Short term fuel trims seems normal bouncing from -3 to +3. O² sensor voltages fluctuate as well. My O² sensors only have about 3k on them.
Not sure whats causing the negative long term, seems like it could just be the charcoal canister purging.

I have not checked hot resistance of the iac, maybe it only fails hot. I do get a signal on both rso and rsc pins which is normal, the duty cycle goes down as it warms up and is steady, flicking the throttle increases duty cycle a little bit but then returns to the previous lower on time.

I have also not checked fuel pressure, its possible that my fuel pressure regulator might not be working correctly, thus causing the slightly rich condition at idle. The FPR does not show any obvious signs of failure.

All of the injector waveforms looked good too, pintle movement and all, i have checked injectors out of the vehicle and they did not leak. So Im sure they are all good.

Only 2 things it seems it could be is a bad iac, or high fuel pressure.

Sometimes while its just idling it sounds like it will misfire a blip or two, and sometimes it seems like it wants to idle normal for about 2 seconds.

Perhaps you could check the throttle position sensor and see if its dropping out? Also may be a good idea to verify your evap solenoid is sealing tight. I did it by using one of those hand vacuums to draw a vacuum and test for decay. You could be right about the canister purging, or it could be that its permanently drawing in fuel vapor. I have the idle problem but with misfires on my 02 mr2. I would think you'd see positive fuel trims if you had a fuel delivery issue, although I'm no expert. Perhaps back probe the tps sensor plug to see if the signal drops out.

did you solve the problem?