High Idle

2001 Taco with 3.4. My idle sits around 1200-1500 rpm. If I rev the engine to 4000+ the idle drops to around 800-1000 rpm. I’ve cleaned the iac and throttle body and replaced the tps. Ideas?

 

Clean the MAF sensor. Probably isn't it, but you never know.

Also, is this at all times? Apparently the engine will idle at 1500ish while it's cold and then lower the idle speed as the engine reaches operating temp. Mine starts at 1500, but by the time it's at operating temp the idle has dropped to about 900. Still a little high, but I haven't cleaned my IAC yet.

 

This is while the engine is at operation temp. I cleaned the maf as well.

 

My only other idea is to check all your vacuum lines and make sure you don't have a leak somewhere. Cracked ends, loose clamps, etc.

 

Thanks. I’ve been doing that and haven’t found anything yet. Is it possible that cleaning the iac didn’t do any good and needs to be replaced. I can’t figure out why the idle would stay low after reving it so high. Once the truck is moved or turned off and back on, the idle is back to running high.

 

Have you tried resetting the ECU?

 

https://www.tacomaworld.com/threads/ecu-reset.225530/

 

I’ve tried it before. I don’t think I did after replacing the tps. I’ll try again and see if there is any change.

 

That didn’t work.

 

Replaced the iac, still acting the same. Any help would be greatly appreciated.

 

When it is in the high idle condition try to manually close the throttle by manipulating the linkage on the front of the t-body. Push and pull along with rotation. If you can get the idle down this way then its a mechanical problem with the t-body/linkage/throttle opener.
If not then look for "engine control" issues. This could be many things.

Gotta go.

 

Helping me left and right. haha I’ll give that a shot. At this point, I hope the t-body is the problem. Get this over with. Thanks.

 

It could very well be a sticky throttle plate like @Dirty Pool mentioned. I've heard of this on T4R.org. If that doesn't do it, I'd try a second cleaning of the IAC.

Did you get this high idle issue after cleaning the throttle body and IAC or did you clean the throttle body and IAC in an attempt to fix the high idle?

 

I’m pretty sure it’s the tb. I cleaned things in response to the high idle. I went out earlier and discovered that the plate does stick open a little. I had to push it closed. I also believe that it has a gap causing the high idle. I have to take it back off to check if I can see light coming through and confirm. After doing some more searching on here it seems like that’s the most likely issue.

 

I have had a rough idle with my 2.7 for about a year now. Not the regular, gentle "rocking" rough idle all the 2.7's get but a very high frequency rough idle down around 600 rpm which is too low.. It's been very annoying although the truck runs perfect once going down the road. I had thought seriously about cleaning/replacing the IAC. I have already cleaned the MAF sensor on a regular basis. I may have my problem solved. We'll see but I'll tell everyone what I did.

I Sea foamed the engine by spraying the Sea Foam straight into the intake. There is a special Sea Foam product that works for this. I just followed the directions. The can has a tube attached to it. Previously, I had run two bottles of Amsoil PI in the gas. Not all at once in one tank but two tanks of gas back to back. It is only recommended to use "PI" once every 4000 miles which I do pretty religiously. This didn't fix my weird idle. I will say this. The Amsoil PI did wonders for me with another vehicle I owned over 20 years ago. It's good stuff.

I then started using Marvel Mystery Oil in the gas and now my idle has settled down and while it still has the slow rocking idle all 2.7's get the jittery, high intensity, low idle is all but gone. Maybe the the "PI" loosened up something and then the Sea Foam loosened it up some more and then the Marvel finally did the trick. I don't know but my Taco is now idling very well at just under 750RPM. I will continue using the Marvel and see how things go.

It's up to all of you with idle problems if you want to try the same thing. All this stuff costs $$$. I have had a rough idle once or twice since this serious cleaning but it does seem the idle has been changed dramatically so far. I've had a very nice idle for about a week now.

Many do view Marvel Mystery oil as "snake oil" but it really does do wonders in certain situations. It's always worth a try. However, I did use other products "before" the Marvel so who really knows what did the trick. All I can say is that my Taco now idles the same as it did at 119,000 miles when I bought it from my dad and now has 166,000 miles on it.

The other thing I have done recently is "rev it". I normally never take my 2.7 past 3000 rpm. Like everyone else I want it to last. As a matter of fact I very rarely take it above 2500 rpm. Since I did this cleaning I have taken it to anywhere from 3500 rpm to 4500 rpm once or twice a week in 2nd, 3rd, and 4th gears.

I suspect that since these engines were engineered too be "beat" it might help to "beat" them once or twice a week. With no load what could it hurt? I'm beginning to suspect that many of the idling problems we have with the 2.7 is because they are always babied and never really worked hard as they were designed to do.

Just think what you have to rev them to when you're climbing a 7% grade with the rated 3500 lbs behind them. Many here on this forum actually do it while the rest of use these things for DD's or light weekend chores or camping and hunting.

Mine is running, and idling, great right now. I'll rev it high a couple of times next week and continue with the Marvel Mystery Oil. Hopefully, my annoying idle is fixed permanently.

 

Took the tb off and discovered that there is a slight gap around the plate. Is this gap big enough to cause my high idle? Also, it seems like the little diaphragm keeps the plate open just a little bit. Not enough to really notice by looking at it, but enough to feel it when pushing the linkage. This is with it off the truck and cold.

 

The gap around the plate must be normal because how would that gap change. It's not like the sides of the plate could wear down. But, the plate partially sticking open is not normal. Does it look like the plate could be dragging on one edge of the throttle body bore? The reason why I ask is there's a guy who fixed his high idle issue by inserting a small washer in his linkage to keep the plate from dragging on one side of the throttle body bore. Here's the link to the thread: From the pictures you posted, it doesn't look like your plate is dragging but I'm not holding it in my hands. If the plate isn't dragging I wonder if you just sprayed some penetrating lubricant on the linkage it would allow the plate to return all the way closed every time. You could also dissemble the linkage and grease it up good to hopefully prevent it from sticking.

 

That "little diaphragm" thing is the Throttle Opener I mentioned earlier. It is doing what it is supposed to do. It holds the throttle plate open a tad when the engine is off via a light spring. This is to allow additional air flow for the starting process only. Once the diaphragm sees around 7+ inches vacuum it allows the throttle plate to close against it's stop, at normal idle position.

A fully closed throttle plate should be real close to but not touching the bore of the t-body. Toyota spec is a 10 deg angle but in real life I have seen values of 9 to 11 on properly running 3.4's. This can be read on a good diagnostic reader as something to the effect of "throttle angle" and gives a value thru the entire throttle range. Not surprisingly this value comes from the Throttle Position Sensor (hint). Observing this value when the truck is acting up might generate some more clues.

The washer or shim trick @Timmah! mentioned has been successful for a number of folks. It only cures the condition where the plate is not centered in the bore and hangs up on one side, usually the rear. That's why I mentioned push and pull on the linkage as a test.

A semi shade tree fix for a fluctuating TPS value is to rapidly open and close the throttle a bazillion times (50-100). This "can" "wipe clean" up the connections in the TPS thru friction. If that works, one should start saving for a new TPS.

 

The plate isn’t catching and I can’t get it to move side to side. Once the tb is warm, it does seem to stick. I can push the linkage down and the idle will drop. Can the throttle opener go bad and stick sometimes? If you rev the engine high and let the throttle body close quickly it will close properly. Its like there isn’t enough force to close it all the way with gentle/normal throttle operation.

 

It could but they are pretty reliable. I can't think of any cases on a 1st gen.

If this is a case of physical sticking or binding, keep in mind that things expand as they heat. Just a thought. This is likely going to take some deduction with thorough manipulation of the various parts of the linkage. A "hold this, wiggle that" sort of thing.
Throttle cable not to tight or sticking?

Late for breakfast.