High idle is driving me crazy

[T4Rscott]

Hey everyone,

I’ve been chasing a high idle since I replaced my valve cover gaskets.

So to recap, I cleaned the TB and IAC, checked for vacuum leaks, tested the IAC coil, and checked my throttle plate. Lubed the linkage as well.

I found no vacuum leaks, the coil resistance was 19.3 cold but I only got that reading once. I ended up buying a cheap Fleabay IAC to try, and I ended using the coil for comparison. I will say, when I used a9v on the coils, my original one did not move.

So now I’m wondering if I should just replace the coolant temp sensor. Does anyone know what the FSM says about testing the ECT sensor?

One last observation. When I inspected my throttle plate, I noticed it was not completely touching when closed. It felt like there was supposed to be there? Has anyone else noticed this? I’m about ready to look for a good used TB.

If anyone has any suggestions, please let me know. In the meantime, I’ll be in the corner rocking back and forth jibbering to myself.....

Scott

 

[Bad Luck]

[MENTION=57676]T4Rscott[/MENTION] It may sound a little stupid, but are you sure the vacuum hoses are routed correctly? I had the same problem after I did my valve cover gaskets. It turned out that I had the vacuum hoses for the ADD vacuum canister and the fuel pressure regulator switched.

 

[brillo_76]

If its after a valve cover job. Triple check everything you took apart. Very possible a simple issue here that has been overlooked.

 

[nissanh]

Probably a coolant temp sensor. I have a landcruiser that maintain its idle based on the coolant temperature. I found out the landcruiser had 2 coolant sensors and one with 1 wire and the other with two wires. The sensor with two wires is for ECU to maintain the rpm. As soon as I replaced it, the RPM dropped to 670 when engine warms up. Before this fixing, the rpm stayed at 1100.

The sensor is cheap and I installed an old 92 corolla sensor into my LC and it worked. OEM is about $15.

Use the graph if you want to measure the resistance vs temperature. I used it and found out truly the sensor is faulty.
Toyota RAV4 Service Manual: Inspection - Engine coolant temperature sensor - 2Az-fe engine mechanical

 

[19963.4lsr5]

The easiest way to check your temp sensors is to see what they read after sitting overnight and see how close they are to outside temp and too each other.


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[gamefreakgc]

The throttle valve not completely closing could mean 1 of 2 things:

1. Your throttle cable is too tight. There needs to be about 1-2 mm of slack for the valve to close completely. When idling in park, grab the pedal and pull it towards you (don't press the gas, do the opposite). If the idle drops, your cable is too tight.

2. Some throttle valves wear over time and causes it to develop a gap. No matter how hard the IAC tries to close the flow, it can't since it's just going straight through the throttle valve. There's some fixes on here that involve using a washer but your best bet is to replace it if you have a 96-00 with a used unit (save your old IAC though, they go bad). If you have a 2001 or 2002, this isn't an option since they cost over $1,000 new and $300 used...

 

[19963.4lsr5]

All of my mopar and my saturns had a very small gap from the factory. It was there to prevent stalling in case the IAC failed or became clogged. I’m pretty sure there should be a small gap on Toyota’s also.

The saturns gap (factory set[emoji12]) was suppose to maintain 500rpm when you blocked the IAC bypass port as an example.


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[gamefreakgc]

All of my mopar and my saturns had a very small gap from the factory. It was there to prevent stalling in case the IAC failed or became clogged. I’m pretty sure there should be a small gap on Toyota’s also.

The saturns gap (factory set[emoji12]) was suppose to maintain 500rpm when you blocked the IAC bypass port as an example.


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I have a reman'd throttle body with absolutley no gap (no light comes through when held up) and it idles perfect. I'm going to go out on a limb and say that the 5VZ-FE throttle body at least did not come with a gap from the factory.

 

[19963.4lsr5]

I have a reman'd throttle body with absolutley no gap (no light comes through when held up) and it idles perfect. I'm going to go out on a limb and say that the 5VZ-FE throttle body at least did not come with a gap from the factory.

Is there a gap adjustment on the throttle plate shaft anywhere?

I had my throttle body gasket on incorrectly when I first put the engine in. My idle was perfectly fine at 600rpm in gear and 750 in park and neutral. The only indication anything was wrong was my P code for engine too lean.

I have a spare throttlebody I picked up at the junkyard a few years ago. I’ll scope it out and see if a feeler gauge fits between the body and plate. Now, where did I put it......Toyota defiantly did certain things different than the American cars and trucks I’ve been wrenching on since the early to mid 80’s. And they use to joke about “Ford and their better ideas”.


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[19963.4lsr5]

I actually have two spare throttle body’s. I found the one on the 96 engine that developed a bad eroded cylinder and sprayed brake cleaner into the opening and the fluid stayed there until I opened the throttle.

How you went from a good idle to high idle doing the head gasket and developing an air gap is beyond me. Unless it’s been like that for a while and you still have a vacuum leak somewhere and now the IAC can’t compensate for it anymore.


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[AntleredRuin]

I never looked down the throat of my TB to check if it was closed, but I've gotten and 'fixed' a high idle multiple times after doing some top end work.

My issue was the Cruise Control Cable.
Pretty much, to 'fix' the issue, I just detach the cruise control and then the idle drops by itself. Once dropped, I put it back on and tighten it back to where it was.
I'm not sure why, but I assume it has something to do with the ECM trying to relearn when the battery is disconnected, and the cruise control cable has a bind or something and is putting too much tension on it. Obviously shouldn't be an issue, especially since I put the cable back in the exact same spot afterwards, but quirks of a 20 YO truck :shrug:
After that first start, I never have to touch the CC cable again, until the next time I do work involving removing it.

I can replicate the issue, and now I just start the engine for the first time after doing work, let the idle drop, and then install the CC cable.

Kinda fun, though. When your drive idle is 1500, you can launch off the line REAL quick.

 

[19963.4lsr5]

This is what I see holding it up to the sun.


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[T4Rscott]

[MENTION=57676]T4Rscott[/MENTION] It may sound a little stupid, but are you sure the vacuum hoses are routed correctly? I had the same problem after I did my valve cover gaskets. It turned out that I had the vacuum hoses for the ADD vacuum canister and the fuel pressure regulator switched.

Yes everything is where it should be.
Thanks for asking!

 

[T4Rscott]

The throttle valve not completely closing could mean 1 of 2 things:

1. Your throttle cable is too tight. There needs to be about 1-2 mm of slack for the valve to close completely. When idling in park, grab the pedal and pull it towards you (don't press the gas, do the opposite). If the idle drops, your cable is too tight.

2. Some throttle valves wear over time and causes it to develop a gap. No matter how hard the IAC tries to close the flow, it can't since it's just going straight through the throttle valve. There's some fixes on here that involve using a washer but your best bet is to replace it if you have a 96-00 with a used unit (save your old IAC though, they go bad). If you have a 2001 or 2002, this isn't an option since they cost over $1,000 new and $300 used...

It is hitting the travel stop. I wanted to know if the millimeter of travel after was normal

 

[brillo_76]

Any updates on this issue?

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[T4Rscott]

Here’s an update.

I removed my throttle body and investigated what was holding the plate open that literal 1mm.

What I found was the part that has the small,1/8th inch vacuum line, is that the dash pot? Anyway, I adjusted the stop screw so that the plate was completely closed. Everytime the idle was high, I would close that gap and it would calm down. I also did the washer mod as well to take out some of the side to side movement.

I still have to drive it to see if there’s an improvement.

I hope it will take care of the issue, as she now owes me after all the parts and body work. She now has stainless rockers! One less thing to worry about living in Maine.

Anyway, I’ll do another update after a test drive.

Scott

 

[T4Rscott]

Final update- success!

After I adjusted the dash pot, it did the sam high idle again.

I removed my throttle body one last time and noticed the plate was off to one side. I ended up finding just the right washer to space it out. There is a perfect light halo around the plate and it now idles properly.

Thank you to all for the help!
Scott