I posted about this problem earlier this year, but eventually gave up when I couldn't find a solution. The problem still exists so I'm giving it another shot in hopes someone who didn't see it the first time can offer some advice. Here is the original thread, but it is long so I will try to summarize below (https://www.yotatech.com/forums/f116...ecover-286355/)

Problem:
-The most consistent problem is the low drop in idle when letting off the throttle. As the engine spins down the idle drops below the idle setpoint before returning to the idle setpoint. Sometimes the drop is small (100-200 RPM) and sometimes it is so significant that the engine dies.
-The other issue is that the idle hunts around the setpoint, sometimes +/- 100 RPM. And sometimes the idle just stays a bit lower than normal (100ish RPM). In other words, not a consistent idle.
-The biggest issue is the big idle surges that progressively get bigger, sometimes until the engine dies. The idle will hold steady, then drop, recover, drop, recover, and so on. The idle really never goes above the setpoint.
-Some days I don't see any surging and the idle is fine. I can't seem to pinpoint what situation causes the surging; however, it seems with colder days (~50F) approaching I've seen more and more surging. I didn't notice much surging during the summer.
-The only code I have is code 11 (AFM). I know my AFM is bad and does not pass the tests, but as you'll see below I replaced it and did not fix my problem.

What I've tried:
-Replace cap/rotor/plugs/wires and set timing (routine maintenance)
-Cleaned & recharged K&N air filter
-New AFM (old AFM was out of spec) but I reinstalled my old AFM after the new AFM did not make a different (AFM was expensive which I why I returned it)
-Cleaned TB and made sure all ports were clear, including idle screw
-Confirmed IACV is operating correctly
-Inspected TPS multiple times (passed)
-Inspected coolant sending unit (passed), but also replaced
-Inspected dashpot system (passed)
-Temporarily blocked off EGR valve to see if it would change anything, no effect.
-Recently I replaced the alternator, but that is unrelated.

What's next?
I know I still have a bad AFM, so I can try another one. Before, a new AFM didn't solve anything so I imagine something else is the culprit. Bad ECM?

The issues seem to come up with colder temperatures, so it seems to be AFM related. Just not sure what to do besides replace the AFM and ECM and see what happens.

Any other ideas would be appreciated!

 

When did the issue start ? Can you post a video of the engine starting up and post it here?

 

Thanks for the reply. I can't pinpoint an exact date when it started, but based on my first thread I'm guessing it was around this time last year when I started noticing the surging idle (right around when it started getting colder outside). The colder weather is really the only sort of trigger I can think of that exacerbates the problem. Though, like I said, some days I don't notice any surging.

I'll post a video of a cold start up, however I haven't noticed any surging on startup. The IACV works like it should and raises the idle on startup until the engine warms up, then the idle drops down to the setpoint. I usually don't see the surging until I drive for a bit and have to stop at a light or something.

 

ok ,well ,we'll see what the video reveals .

 

Btw, if you swapped in a new afm and it didn't fix the issue or clear the code, then you may have a wiring issue from the afm plug to the ecu.

 

I took a video this morning from starting up cold and letting it idle until it warmed up. I then drove it a short ways and then parked again. It was pretty warm out this morning, only 60F, and it acted better than normal.

The surging doesn't really start until I have my foot on the brake. That's another thing I've noticed; however, I've seen the surging and low drop happening without touching the brake. So, it's hard to say something with the brake is causing it (either something with the vacuum or just the brake signal to the ECM).

[YOUTUBE]DZ1cBVbCWwI[/YOUTUBE]

Here is another video I took on the way home from work a few days ago. Sitting at a stop light and it was really surging good. My foot was not on the brake. Had to cut the video short because the light turned green, but if I would have sat there longer the surges would have gotten bigger and bigger.

[YOUTUBE]KlqL8ozR6uM[/YOUTUBE]

I thought about this, too. Definitely something I have to look into.

 

ok , I've done a lot or reading this morning .i'll list A few things that have solved surging idle ,some you may have tried ,

1)Clogged coolant lines at the iacv .
2)air in the coolant system ,I've heard it you raise the front of the vehicle when you add coolant it will prevent air from entering or allow it to escape .
3) Blown headgasket / eroded water jackets .Compression test?
4) Another guy said A ground strap on the rear of the head (driver side ) was his issue .
5) vacuume leak , you can make a homemade smoke machine,check youtube , I make one awhile back works great.
6)http://www.toyotanation.com/forum/80...itive-fix.html

 

Thanks for digging around for me. There seems to be two different types of 'surges' that I ran across while doing some research. Most people report the surging as the idle surging ABOVE the idle setpoint, where my surge is more like dropping below the setpoint (is it even called a surge at that point?). Anyways, some issues you mention are the high surge, but I didn't really come across anything exactly like the issue I have.

1) This is where I started. A clogged IACV causes a high idle, but when the ECM sees a warm engine and a brake light signal fuel will be cut causing the surge. Different issue than what I am seeing.

2) Similar to #1. I think the air bubble coolant system can cause the IACV not to work properly or give an incorrect reading on the engine temp sensor. I can't remember exactly.

3) I hope its not a blown head gasket; I put a new head on it less than 50k miles ago. I can do a compression check. Maybe a bad head gasket causes a vacuum leak, raising the idle and causing similar issues as if the IACV was clogged.

4) Ground strap idea is interesting. Do you have a link to that thread?

5) I was thinking it may be a vacuum leak somewhere...I just wish the problem was more consistent (which is what I'd expect if it was a vacuum leak). Was leaning toward the brake booster being the issue but really not sure. I think double checking for vacuum leaks will be a good thing to rule out.

6) Not likely since I see the issue without pressing the brake pedal, especially the low drop. Also, no AC on my rig.


I want to say it is related to the AFM since it is throwing a code, but I vaguely remember testing the AFM years ago when diagnosing something else and it did not pass the tests. I may have even swapped in a new AFM back then thinking that was an issue (but later putting the old one back in)....I can't remember exactly.

 

Here is the link https://www.yotatech.com/forums/f116...32/index2.html

"tysen86 " mentions it . ground strap for block not head.

 

This issue seems to point to an intake leak that the engine is having a hard time compensating for.

Check make sure there are no intake leaks between the AFM and the throttle body. Check for intake air leaks around the inlet manifold and vacuum lines. A leaky brake booster may be a problem since you said it worsens at times when pressing brake pedal.

Could be an issue with the throttle body. Possible PCM problem?

Another note, listening in the videos, the engine seems like it has some health issues. I hear several exhaust leaks, and there is valve train noise and combustion issues. Any obvious health issues should be corrected first.

 

Thanks for the reply.

I feel like it is something with a vacuum leak. I just wish it was more constant so I could zero in on the problem. I think a smoke machine is in order to see if I have any leaks.

I went through the TB very thoroughly last time, cleaning out all the ports and making the correct adjustments. Didn't see anything obvious.

Could be the ECM/PCM.

As far as the health issues, there is definitely exhaust leaks at the collector and muffler, downstream of the o2 sensor so I don't think the sensor would be getting weird readings (no codes at least).

The valve noise has always been there, on the old and new head. The valve lash was recently adjusted (also, you may be hearing the camera mount rattling in the video). I haven't noticed any combustion issues...I did have a slight miss last year but that went away after I went through the ignition (cap/rotor, wires, plugs).

 

Hey I was wondering what you ended up finding out about your issue. A few months back (when it got cold) my truck started doing the same thing. It’s a newer engine, less than 30k on it, and we ended up adjusting the TPS and the problem went away for a while. It became an off and on again thing, but Just a few weeks ago the problem started getting worse, to the point of the idle dropping so low it would die, and I did notice it seemed to happen more while braking. Haven’t tried replacing my AFM yet, and know that I probably need to (it’s from an older 22re found in a junk yard)

Id appreciate any advice for what you did and what seemed to help you out!

 

Unfortunately I haven't figured out what the issue is. I had planned to check for vacuum leaks but never got around to it...that was the only thing left on my list of possibilities. Now the truck is no longer my primary vehicle so I kind of just gave up. When I do drive it, the issue does show up once in a while but for the most part it drives find so I'm just living with it. I did replace the entire exhaust, but that didn't seem to make a difference as I expected. I really think (hope) it's a vacuum leak somewhere...as you can see from this thread I did a lot of trouble shooting with no luck. Let me know if you figure out what your issue is!

 

Believe it or not, frequently the idle going very low when braking can be caused by nothing more than the idle being set too high. The ECM cuts the fuel, I think at the injectors, but I'm not certain, when the RPM is above the specified idle setting for that specific truck when the brakes are pressed. Once the RPM drops down to the correct idle, it allows the fuel to flow again. If the RPM at idle is set too high, I think above 1200, but I may well be wrong on that, the ECM may not react to allow the fuel again. Thus, apply the brakes, the engine runs down and dies.

As for the rest, a possibility is either a vacuum leak at the corners the big air tube between the AFM and TPS takes, they get brittle and can have cracks in them that are hard to see, or at the idle adjustment screw on the throttle body. The idle adjust screw has an o-ring on it, and if it gets old, brittle, or damaged some other way, it can allow too much air past the screw.
Easy to check the idle adjust screw. Screw it down to the bottom of it's adjust range, making sure to count precisely how many turns, including fractions of turns, it takes. That way, when you re-install it, you know where it was, so you have a good, ok, decent, starting point. Then you unscrew it all the way out to check the o-ring.
O-rings for replacement that fit the screw are pretty readily available.
A note on making the o-ring last longer is to apply a super thin layer of Vaseline to it when you install it. It makes it seal better, and last a lot longer. Then, of course, you'll need to set the idle RPM correctly. If it's very different than where it was set before, you might want to check/verify the timing again.

I don't know for sure if any of this is the slightest bit useful, buuuuut...
Pat☺