Stumped by High Idle

[dtc81]

My 99 4runner 3.4L manual trans with cruise control developed a high idle a few weeks ago. (I have searched the internet high and low for ideas, and tried a lot of fixes, so bear with me). The timeline of issues and attempts to fix are as follows:

3 weeks ago:
Randomly had a P0120 TPS sensor switch A circuit appear. Cleared it, never came back.

2 weeks ago:
Throttle started getting "stuck" at around 1700 rpm occasionally, then by driving it or tapping the throttle, it would drop to 800 rpm and idle normally.
Attempt: I cleaned the throttle body and IAC, as it seemed to me the IAC was sticky. It was very dirty. I reinstalled everything and the problem persisted.
Attempt: Purchased new IAC and noted how much smoother valve rolled open compared to old. Installed new IAC. Problem of idle getting stuck was fixed. Now a constant 1300rpm idle existed.
Attempt: Installed new TPS just because. Left battery disconnected overnight. Drove truck with new TPS for 2 days, idle dropped to 1000rpm.

1 week ago:
Truck drives fine, but idle never drops below 1000rpm. I can manually push the throttle linkage "down" and get it to drop to 800 rpm and it will stay there until I open the throttle manually or by the pedal. Cables are properly adjusted, all vacuum lines are in good shape and checked for leaks. Fuel trims are normal on my scantool, so that seems to confirm no vacuum leaks, and engine comes up to temp normally and stays right around 190-197 degrees. The one thing I noticed is that the butterfly doesn't seem to fully close, as if the return spring is weak and can't snap it shut 100%. That would explain why when I push the linkage to close by hand, it idles normally. I made sure the dashpots and stops were properly adjusted as well. Everything seems fine there.
Attempt: Purchased a used throttle body from a salvage yard. Cleaned and installed my new TPS and IAC on that throttle body. Problem was worse.

Now I'm at the point where I returned the salvage yard TB, installed my original TB, and am just running it with a 1000rpm idle. It's driving me nuts.

Any ideas?

 

[nobb]

When you clean the TB too well, the gunk that was helping the TB seal is now open and lets more air flow. How much play do you have in the TB butterfly? There is a washer mod that might help. However, in my case I had to install an extra linear spring to help force the butterfly to close tighter.

There is some sort of self learning that the ECU does to compensate for this throttle wear but it only seems to be minor and I cant figure out it works. You can use an OBD reader to see the reported throttle position. After the washer mod, my throttle would only close to 10.2% which resulted in a ~1300 rpm idle. Installing the return spring helped it close to 9.80% and a normal 700 rpm idle after a few on/off cycles to help the ECU relearn.

 

[dtc81]

Thanks nobb! I'll plug in my tool today and see what the percentage is at idle. How did you mount your helper spring? I was thinking about doing something around the same, but want to make sure it doesn't interfere with anything. Hopefully I can find a light spring rate so it doesn't make my pedal real heavy.
I figured cleaning out some of that carbon and gunk in the throttlebody hurt the seal. I've seen the washer mod, but mine would have to be a very thin washer to make it work. I'm not sure if that's exactly the problem, I think it's the spring


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[maxbrown11c]

I did the washer mod as well but it eventually started idling high again. I used a light helper spring as well to pull it closed. Pedal still feels the same as before, no extra resistance from the spring.

 

[maxbrown11c]

That is the spring I used. I am pretty sure I got a pack of them at Lowes but it might have been Home Depot.

That's how I mounted mine. It's been idling fine for over a year now.

 

[dtc81]

Thanks maxbrown. I'm gonna give that a try.


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[nobb]

This is my return spring setup. I would make it more inline so it doesnt rub on other components. It's better to start wih a lighter spring so that it doesnt affect pedal feel. You'll need to do some tweaking to get the tension just right.

 

[nissanh]

The gas paddle is super hard to press even with the stock spring, how do you all manage it with an additional spring? My leg always hurt after a long drive.

You can lube the axles on the butterfly valve to make it close better.
May be I am treating my trucks too much!

When you clean the throttle body, It is best to remove it off the engine and turn bottom up. This makes all the gunk to flow out instead going right into the IAC.

For the OP: do above and remove the IAC off the butterfly valve. Clean the vale body well with cleaner and get the gunk out. Hint: use a good Phillips screw driver. Tap the bolt once before attempting to remove; this prevents the head getting stripped.

 

[dtc81]

Thanks nissanh. Yeah I already pulled the TB and cleaned it, and replaced the IAC.

On a side note, I threw the spring on and it pulled the idle down to 900 rpm... we may be onto something herep


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[baja1]

if all else fails....search "manually operating the IAC" it works!

 

[nobb]

Adding a light spring doesnt really affect the pedal feel by any noticeable amount. A heavier spring will mostly cause the throttle to close too fast...which means the rpms drop too fast in between gear shifts (manual drivers) which is annoying for rev matching.

 

[maxbrown11c]

How you can test to see if you need to add a washer to your throttle body linkage is give the throttle cable linkage a little tug when your 4Runner is warmed up completely and the idle has stopped at one place. If it goes down more to 650 or 700 then you will need a washer "spacer" in the linkage to keep it in that more outward position. I like the way nobb mounted his spring, I will probably bend that tab and mount mine the same way soon.

 

[Oview]

That is the spring I used. I am pretty sure I got a pack of them at Lowes but it might have been Home Depot.

That's how I mounted mine. It's been idling fine for over a year now.

This is great. I'm having the same issue. After driving, I'll put it in park, and it idle at around 2000-2100. Also, whenever I let off the break while in drive, it will increase in speed like I'm on the gas. The check engine light just came on as well and I'm noticing a heavy exhaust smell while driving. Hmmm.

 

[dtc81]

I added the same spring. It pulled the idle down to around 900 consistently. I am going to try the washer trick this weekend in hopes proper plate alignment will help a little!


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[nobb]

I added the same spring. It pulled the idle down to around 900 consistently. I am going to try the washer trick this weekend in hopes proper plate alignment will help a little!


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If your idle is now at 900 rpm, it's likely that the ECU will gradually relearn in the next few drives and drop your idle back to normal. Not sure if the washer mod is good or bad with regards to affecting the throttle wear surface.

 

[19963.4lsr5]

Do you think it's pulling air through the throttle shaft bearing seals after your cleaning?


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[jwsav]

High idle issues

Check your pcv valve, if its stuck open it will cause it to idle high. Your tps also controls idle. If its not properly adjusted it will cause a high idle. Alot of the time, a high idle is a vacuum leak. These trucks have issues with brake boosters which can also be loosing vacuum.

 

[Benski]

I had high idle too!

I noticed my idle at 1500-1700 rpms a week or so ago. It was persistant and wouldn't drop even after fully warmed up. I saw the videos of cleaning the throttle body and IAC. I did both of those and still had a high idle. I went to a mechanic who said spray carb cleaner around all of the hoses to see if there is a leak. It would suck the spray in and bog down. Nothing happened when I sprayed around the hoses. I looked at some more videos and checked on here. I realized I hadn't checked my Mass Air Flow Sensor! I removed it and carefully used a Qtip saturated in carb cleaner to wipe the sensor wires up in the unit. I put it back in and now the idle has dropped to 1000 rpms and if I manually press the throttle closed it drops to 700 rpms. I may need to put a spring on it to help it close fully but for now I'll let the computer adjust itself. These threads help soo much! Another happy camper!

 

[wrpsuite]

Bump

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[Devbot]

Bump

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The hell are you bumping? :wacko: