DupermanDave

This is sort of different than my other posts. But here's what's going on.

My idle has been slowly climbing over the past week. At operating temp, it would idle at 800 rpms. Now it idles at 1100 rpms. The idle screw is all the way down, and even with the TPS unplugged it idles at 1100rpms. When I jump the diagnostic terminals, it still idles at 1100 rpms. I cannot get it back to spec 800 RPMs. It also surges up and down again, just as it was doing before I adjusted the TPS.

The engine is timed dead on. I timed it just last week. And with the engine timed, it still idled at 800 rpms. I tested and adjusted the TPS about a month ago. That fixed the surging issue. I retested and didn't have to adjust the TPS just this morning.

Yesterday I spent the entire day removing the throttle body in order to clean the IAC/IAV valve. I got the entire thing apart and cleaned it. It was very clean to begin with. I also cleaned the inside of the throttle body and the EGR valve. EGR was black with soot (is that bad?) so I sprayed some wd-40 and carb cleaner on it and got it looking good. After everything was back together, there was a problem. I started up the truck, and even without me pushing the brake pedal the engine surged up and down and up and down. It did this all on its own. It did it as soon as the engine turned over. It has since stopped, but I thought this may be important to note.

So I'm lost. There's no vaccum leaks, as I sprayed the carb cleaner over all of the gaskets and hoses to verify no leaks. The rubber hoses are all tight and secure. Coolant level is good (and full). Coolant system has no air pockets. I'm at a loss. I want to think it's a bad TPS, but even with the TPS unplugged it doesnt change anything. I read that this elimates the TPS as the cause.

Coolant temp sensor is brand new. I also tested the O2 sensors and they are both okay and within specs. They're still going to be replaced in a week or so.

So what else should I look for?

TNRabbit

There was JUST AN EXACT THREAD on this recently (OK, every WEEK); most likely a VACUUM LEAK or your TB butterfly isn't seating properly.

DupermanDave

I've been searching and reading. Most of the threads have no solution and just come to a sudden end. That gets annoying. On some of the solutions I have found, one guy figured out his idle adjustment screw worked its way up and loosened itself. Not the case with mine, as I check it every time I park.

The butterfly valve is a possibility. How would I test to see if it's seating properly? Feller gauges?

TNRabbit

You should be able to tell right off if you take the intake hose off & take a close look. If it's the problem, I'd guess you'll have a lot of carbon/gunk buildup there.

You can use a propane/MAPP gas torch (UNLIT!!!) to check for vacuum leaks while the engine is running (it will idle up where the leak is). This is the most reliable method I've ever used for finding any leaks. Good Luck~

DupermanDave

So just let the gas leak out of the propane tank and wave it around the hose bases and gaskets?

TNRabbit

You got it~...except I'd be a little more deliberate than "waving it around".... hehehhehe

desert-rat660

sounds like u have an airpocket at the iacv

DupermanDave

I thought it might be an air pocket, so I burped the heck out of the air system. Squeezed coolant hoses and got every bit of air out of the system. It's still a possibility.

in this thread https://www.yotatech.com/forums/f116...r-idle-178801/ it was suggested it might be the gasket I reused. I got today off and I'm going to try and replace the gasket where the throttle body connect to the intake manifold.

Should the new gasket not fix the issue how would I get the air pocket out?

desert-rat660

i had that problem the only way i could get the air paocket it out was to remove the coolant hose to the left side of the throttle body, i removed it while it was hot but only for a second. no more surging idle

DupermanDave

Well, it's not surging any more since I took the throttle body and IAC off to clean them. Now it just idles at 1500 RPM and the idle screw is all the way in. Might be a vacuum leak, so today I'm replacing the intake plenum gasket.

thaddeusss

there's two other possibilities for 'hidden' vacuum leaks besides the IACV. one is a valve on your power steering pump that is supposed to bump up your idle when you hit the turning lock, which can stick open, and the other is the air conditioning idle-up valve which can also stick open.

I recently fixed a very difficult high idle on my truck, which turned out to be a worn-down throttle valve. it was closing properly, but the side of it had worn off from friction and was leaking enough to cause a 1300 rpm idle with the air screw all the way in. when I cleaned my very dirty throttle body it just made things much worse - there wasn't gunk blocking the air anymore. take a close look at your throttle body. I would never have noticed the big gap (really barely more than 1/16") if I hadn't held the body up to the light when I was cleaning it, so I could see the crack.

I even took my truck to a very highly recommended toyota-only mechanic, who treated me like an idiot and tried to convince me that the throttle stop was too far open (it was at factory spec) and when he backed it out so the throttle plate was jamming in the body, and not contacting the stop at all, he blamed the sticking on the black goo and sticky cables. when I got the truck back I could only stand to drive it for ten minutes with the still-high idle, that varied depending on how stuck the throttle was, and having to stomp on the pedal to get it unstuck. I promptly put the throttle stop back where it had been.

good luck!

oh yeah - you can test whether it is a 'bubble' in the IACV by putting a piece of duct tape or two over the port in front of the throttle plate and then running the truck briefly. that keeps the air from going through the valve. doing that test, if your idle drops only when cold, your IACV is working properly, if it drops when warm, the IACV is your culprit.

DupermanDave

this port you speak of. is this the little hole the size of a dime on the bottom of the throttle body near where the intake tube connects to the throttle body and in front of the butterfly valve?

i dont have AC, so that couldnt be it.

I just changed out the gasket and got everything back together. havent started it yet to test it.

Windsor

The easy way to find air leaks is to get a can of wd-40 or starting ether and tactically spray an area and then listen to see if your idle improves.

TNRabbit

.....

DupermanDave

I've already sprayed the lines with a propane torch I borrowed, and also used a water bottle to spray the entire vacuum setup. Still no change in idle.

DupermanDave

So here's the scoop so far

I started up the truck with a new intake gasket. Still idles at 1500 RPM. I drove all the way to my parent's house...still 1500 RPM. At my parent's house, I put duct tape over the IAC hole in the throttle body. While the engine was cold I started it up and it idled really low. As the engine heated up the idle slowly climbed to 1500 RPM again.

So I guess the problem isn't the IAC? Could it be the gasket inside the IAC?

I'm about to sell this thing and get a beetle. (nah, I love this truck too much, but I'm getting depressed about it.)

-edit-
forgot to add that I also removed the hose from the side of the IAC to burp out any air pockets. I re burped the entire cooling system.

sb5walker

What happens when you completely block the intake of the throttle body?

What happens when you tape both the lower (iac) air bypass and the upper hot idle bypass?

Were you able to verify that the butterfly is not worn and is not leaking?

BTW, disconnecting the TPS does not eliminate it as a cause of idle trouble: the IDL and E2 terminals (the bottom two, I think) are supposed to have continuity when throttle is at idle. If you disconnect the tps, they won't. Therefore if you disconnect the tps and your idle doesn't change, that would more indicate a bad (or misadjusted) tps than a good one.

But still, air has to be getting into your cylinders somehow, and that's likely where your trouble is. (It wouldn't hurt to verify IDL & E2 have continuity at idle, though.)

Take a good look at everything that plugs into the plenum - egr tube, and every vacuum hose. I know you've looked for vacuum leaks already, but they are notoriously hard to find. Did you check the full length of the brake booster hose? You might try removing it from the plenum and plugging the plenum fitting.

Buck up - if you keep eliminating possibilities, you're bound to find the cause eventually.

DupermanDave

so next I'll check what happens if I block off the intake to the throttle body. How would I go about properly doing that? Just remove the intake tube and block it off with a rag?

second, I'll go ahead and check the upper AND lower air bypasses. But...where are those? I know where the lower one is, but I've never seen (or noticed) the upper one.

I would think the butterfly is fine, since it was working fine before I removed the throttle body from the intake plenum. I haven't done anything to the butterfly valve, so I would think that this would logically eliminate the butterfly valve.

There is one upside to all this. My after fire went away, lol.

DupermanDave

I went out and plugged the upper and lower idle intake bypasses. When warming up the engine all the way up to operating temperature, the engine idled at 1000 rpms. still not 800 where I had it, but what does this reveal?

lilgreg46

I work in a shop for a living and the best tool I have in my box is a "smoker". This gem has saved me hours on tracking down leaks and made me look like a hero more than once. What it is a small heating element that heats baby oil to the smokeing point and pushes it into the engine at about 1.5 psi through a vac line ( I like to use the brake booster as it is easy to get to). Simple to use, disconect a line ( vac) and plug it in, look for smoke comming out and you found the leak! The point to this is you can either make one now that you know how they work or call around and ask if a shop local to you has one. The one I have is at this site http://www.redlinedetection.com/products.htm
Might help you understand what I am talking about. I hope this helps you....