One more high idle problem to troubleshoot. 2001 3.4 liter auto/air

This looks like the best place to ask for help- looking all over the internet too. You guys should be proud to be the Taco gurus.

Anyway symptoms are fast idle before IAC and TB clean out. was like 1800, now about 2000.
Previous owners (5) and lots of miles 285,000.

I'm getting confusing readings from the AutoZone scanner- it can't read my VIN so I don't trust the "findings" like today it said MAS airflow sensor was bad.

Previous to my cleaning out the IAS and TB with TB cleaner only it was flagging the catalytic converter.

I had a good crawl under the truck and the previous owner had tried to replace the upper O2 sensor with an aftermarket model and managed to get it on wrong so that the adapter plate was bent and the O2 sensor was not seated flat against the top of the exhaust mounting point.

However, there was no mention of an O2 sensor at Autozone or Orielies , so I'm hoping that the O2 is happy.

But here is the scary part- Took the truck to my favorite mechanic today to get his opinion- he even dragged out his own high dollar Launch scanner on his lunch break, but there were no numeric codes, so I can't tell much from that. he did say to look for a vacuum leak and the catalytic converter was showing "low efficiency" whatever that means.

And I have been reading your mail a lot to try to get a handle on this OBD -2 system. My 1991 was a lot easier LOL! but not so pretty.

Anyway - I'm in the middle of testing the old OE IAC. The upper and lower magnets are both showing about 22 ohms at room temperature and the center pin of the harness has 12.2 volts on it to ground. I did simulate the actuation of the IAC off the truck and it does move in both directions although it favors closing (I think) and it was pretty gunked up like the bore of the TB.

I did not change any of the physical settings on the TB - anticipating that someone on here would think it a bad idea and now there is a starting point at least to troubleshoot from.

I went to Harbor freight today also and bought a Vacuum tester. The intake manifold vacuum is changing at the 2000 rpm so the needle is almost a blur. (very rapidly) between 15-20 inches of mercury with my fast idle at 2000, so the instruction manual is hinting at sticking or burnt valves, but when I pulled the PCV valve to check for blowby there was nothing at all. Of course that could be because of the fast idle?

Another factor is when you start it up from cold it runs about 5 seconds at around 1200 like the cold choke idea is working fine, but after that it is non-stop 2000 from then on.

So it likes to do about 50 down the road with no pressure on the gas pedal which is way too fast to be safe.

Funny thing is with the PVC out and it's hose disconnected it idles rough at around 500-600 and wants to die.

If I hook up the PVC and pinch it off it drops from 2000- to about 1900.

There is zero smoke from the tail pipe and no obvious vacuum leaks although all the hoses look original (dried out)

Tomorrow I'm going to check out the vac hoses again more thoroughly as the previous owner has swapped the auto trans completely and also the A/C clutch does not engage when you try to run the A/C. - Q does the A/C get fed some vacuum?

 

Keep in mind I'm dumb, but first I'd replace all the vacuum hoses and intake tube, which I did on mine. If they're original they're shit now after 23 years or will be when you touch them. If not fixed, do the throttle body gasket and intake plenum gaskets. Clean the MAF sensor. No shop mechanic ever takes care of that stuff. It might not fix your problem but it's at least a problem.

 

Another thing you can do if you're hunting for vacuum leaks is get a spray bottle and fill it with water. Spray it over everywhere air could enter/escape. If it's a vacuum leak, it'll hiss and bubble. I used to drive a Mitsubishi Montero 2003 and man Mitsubishi of that era was vacuum leak nightmares, especially my 3000GT I had.

Generic note on 02 sensors. While it may not cause your slightly high idle, a obd scanner may not pick up your up stream sensors as defective and instead point to other issues like your cat. likewise with a vacuum leak, I've had o2 codes because my Montero's vacuum leak confused the truck into thinking the o2 or the cat was bad.

Also.. I've worked at oreilys and AutoZone in my younger years. don't rely on them for vehicle diagnosis. instead, buy a $25 bluetooth OBD scanner off of Amazon.

https://www.amazon.com/gp/product/B073XKQQQW?ie=UTF8

 

Good ideas- hard to do. There's not much room behind the engine next to the firewall and you can't really see much, but the hoses are not brittle. I did spray some carb cleaner back there and got an increased RPM while spraying , so I know there is something wrong back there- hoping it IS a hose or a bad connection. But tonight I found that the oil filler cap was not on very well which the BING AI said would create ANOTHER vacuum leak. I also cleaned the MAF sensor and the air filter and the intake tube and inspected all of that, but anything BEFORE the throttle body should not lessen the vacuum that the intake manifold is seeing. I also replaced the throttle body gasket and the IAC gasket as part of the IAC and throttle body cleanout. I also replaced the PCV valve and put a new piece of vac hose on it. (that was before I found the oil filler cap was loose) so maybe tomorrow when I put the inlet hose back on and test it, the vac leak will be a little less severe, but I KNOW there is another leak behind the engine because of the carb cleaner test.

 

That lack of vacuum could really confuse the OBD 2 system since some of the systems are vacuum operated or controlled and the drastic change caused by the vac leak in the fuel to air ratio could make the OBD think that the O2 sensor or even the CAT was not working right. The O2 sensor does not have a vac connection directly, but a bad vac leak would throw off the rich/lean computation of the computer so much that it might throw those codes anyway. I'm building a DIY smoke machine myself so that I can attempt to pinpoint the leak behind my engine and go from there. Dumb me I did not think to check that the oil filler cap was on tight and sure enough it was loose tonight when I checked just now. But even so- My leak will get stronger now that the oil filler cap is on tight. The leak will follow the path of least resistance no?
I also found that both control lines that go to the IAC valve from the computer are dead/open at the computer. The wiring is good, but pins 15 and 16 of E8 are just a very high resistance with no voltage outputs to the IAC, so after I get the VAC problem sorted out I still will need a new computer module.
I noticed that about half of the gold plated pins had lost their gold plating and were starting to corrode.
I sprayed some AC50 on the terminals and re-seated them several times, but that won't fix the two dead outputs that are supposed to control the IAC valve and the idle speed.

 

You like the Veepeak? I don't mind spending a bit more on a good scanner, and I need one that is bluetooth so I can drive and get more information on the road, but have you ever needed or wanted more information than what this one can provide? Can you say that this one could at least point me in the right direction if I have a vac leak somewhere?

 

It absolutely can. I use it in my racecar for live data as well as in my shitbox to record and analyze o2, Map, boost, temperatures etc via live stream. It'll tell you everything you want to know and for not a lot of money.

It sounds like you are on the right path. Keep us in the loop.

 

It doesnt take much slop in the throttle body bushings for air to leak past the throttle plate and cause a high idle.

 

Removing the 2 intake plenums isn't that bad and will give you access to all hoses. If you have EGR then that takes longer to remove with it and requires 3 new gaskets too.

 

I could see how water could hiss and bubble if it was sprayed on the exhaust manifold, but that would be from the heat and possibly from escaping gasses. But water sucked in to the intake would just dissapear and possibly slow the engine RPMs down a bit if it got sucked into the cylinders. That would still be useful information because of the location of the spray and that is VERY important. It is also much safer than carb cleaner or propane which are pretty scary to use, but it does not evaporate instantly like the carb cleaner or propane, so it might not be quite as quick to react and you might have to wait for a while to be able to isolate the reactions between sprays. However If my smoke machine does not show where the leak(s) are, I would rather use water than carb cleaner any day! Great idea! And it's FREE!

So today the 14th was my Friday the 13th I guess- a couple of packages containing my Haynes service manual and parts for my smoke machine went missing.

Also a couple of fire extinguishers. What a bummer. I knew that some other parts of the smoke machine would not be here today, so I hooked up a low pressure line (Air) to the intake manifold to try and find my Vac leaks the hard way. Made a blank off plate for the Throttle body and did plug as many vac lines and openings as possible, and although the wife was helping we were never able to actually find and identify any real leaks inside the Tacoma. There was some hissing going on, but it turned out to be the air line output of the compressor and not the Tacoma. Meanwhile the trains kept rolling by and between the compressor running, the trains every 15 minutes and the leaking compressor fittings it was pretty much a waste of time.

I am accumulating a lot of HF stuff to help with the hoses and learning a lot about the vacuum system "the hard way" but I think the smoke machine will be a lot more accurate and quicker than the low pressure air and soapy water trick with all the noise we had today - that is assuming that the supplies do actually arrive to our place and stay in the mail box long enough for us to grab them! LOL!

When we do get all our supplies and a successful smoke machine is born, I am assuming that even the exhaust pipe needs to be plugged? Otherwise the smoke could make it past an open intake valve and maybe an exhaust valve and all the way out the tailpipe and reduce the pressure in the intake manifold enough to keep the smoke from finding a very small leak in the engine compartment? That does make some sense now that I think about it.

 

Well I don't know if I have EGR, but I probably do. When my manual shows up it will hopefully shed some light on how to proceed, but I could end up needing a Factory Service manual. Problem is you don't know what you don't know. I did see a You Tube video on how to replace all the intake manifold gaskets and it looks like quite a chore. True you would have access to all the hoses, but any attempt at smoke testing anything would have to wait until all of it was back together! I don't mind doing the work if it is needed for sure, but I also don't want to tear it all apart only to find that the problem was just a leaky hose.

The previous owner had a young son who replaced the automatic transmission and there is a possibility that something was not put back together correctly or just from all the years of wear and tear, but either way there is definitely a vac leak or two at the rear end of the engine compartment.

I might take the hood off and that would definitely improve the access too. I'm really hoping that the problem is a hose, but I will do whatever it takes to find the problem(s) and put an end to them because that fast idle is a bitch to live with.

 

I did find a small amount of wear where the butterfly plate was rubbing on the bore of the throttle body, but the butterfly plate does not sit all the way closed anyway with this mix of missing inputs for the IAC valve from the computer and vac leaks of unknown origin. I noticed that the butterfly plate was still in pretty good shape for a truck of this vintage so I'm going to put that on the back burner for now and look for the larger leaks that we found with the carb cleaner trick first. Rest assured though your point is well understood and taken seriously. Thank you! I also noticed that there was some aluminum corrosion between the flat flanges of the front of the intake manifold and the back end of the throttle body. Not sure how to seal those up other than maybe some high temp silicone sealer because it would be almost impo$$ible to machine them flat again. And on the intake, you'd have to remove the studs and fly cut the face again- risky business? I have a mill, but I don't want to risk busting off a stud in that aluminum casting, so it's either JB weld or silicone treatment. I pressure tested the TB and IAC by itself with my home made blank off plate today and got fairly low leakage, at least not many bubbles were appearing at the blank off plate interface, but of course there is still the corrosion on the intake manifold to deal with and maybe between the two of them they could have been leaking a bit. At least some water was getting between the mating surfaces for sure. I guess water sits in there from condensation on a rainy day and the idea that there is a sort of wetness to the air being ingested and the fact that it's a low spot. that area is definitely under a lot of chemical stress. also my soapy water test would never catch that leak as it is on the bottom side of the throttle body and you can't really see anything if the TB is on the intake already. I might get a better feel for that leak if I just left out the gasket and bolted the TB to the intake bare bones to see how bad the corrosion really is. What sort of remedy would you recommend?

I could feel a small air leak escaping right under that joint even with the new gasket installed and the bolts pretty snug, but I was not really sure from which direction the air leak was coming from, so it's anybody's guess from which it came.
Here's an idea- clean the faces with some diluted Muratic acid, neutralize it with baking soda , wax the blank off plate well and squish some fresh high temp silicone sealer in the cleaned up pits of the corroded area. Then while wet, bolt down the flat of the blank off plate and let it go off for 24 hours. (would epoxy be better for this? That should leave a sealable surface for the gasket (s) mayby use two gaskets?

Note - two part epoxy will harden without any air getting to it while the silicone will not. However, epoxy is not known for being tough enough for higher temperatures in general.

Maybe this would work?

https://www.amazon.com/J-B-Weld-379...05&mcid=7a1b30bcfbeb3aaa9257f655a9b085f7&th=1

 

Your inputs are most appreciated!! Question- A little off the vac leak subject, but If I need an ECM module, where is the best place to find one? 89661-04821 for my 3.4 liter Auto Trans 2001 tacoma? And is there any way that the ECM would shut off the outputs to the IAC at times and turn them back on at other times like for which mode it is in? I'm missing the open and close signals for the IAC at the outputs pins 15 and 16 of E8 on the back of the ECM and my wires to the IAC check out fine.

 

Update- 9/20/24 So I built a DIY smoke machine and tried it on this leaky 3.4 Tacoma I had the compressor pressure down to about 3 psi. but the leak is so fast it diluted the smoke too much and where ever it is coming out it is not visible with the naked eye and also quiet enough that there is no hissing that I can find. The baby oil vapor is hot and it cools considerably when it touches the cold engine parts creating a liquid again. It also stinks up the garage. I don't really have enough instructions/ ideas to pursue the smoke test much further. Do I plug the exhaust pipe? the brake booster? What else? There is a steel male pipe opening on the front of the plenum that I used for the smoke test. Is that a good place to put the smoke in?

Also tried the soapy water idea and low pressure- Found the fuel injector gaskets at the base of the fuel injectors were oozing air and making bubbles on the passenger side. Of course you can't see the ones on the driver's side, but I would expect them to also be leaking a bit if the ones on the passenger side were leaking right?

I have made good plugs for the hoses leading up to the plenum on the pass side and the front, but I don't see any leaks on the driver's side or the rear with soapy water in the cold engine, so I did not attempt to do any plugging for those areas. Plus the rear of the engine is pretty hard to access.

I built a U shaped bridge out of 2x4's to lay on and now I can see down behind the engine a lot better, although there are some heater hoses and the wiring harness are still in the way.

What is the Y connected vac line behind the engine on the 2001 3.4 auto? It snakes between the heater hoses and the wiring harness and one leg of the Y goes to the IAC valve. One other leg seems to be coming from a tube leading down towards the auto transmission. the third leg seems to be coming from the passenger side somewhere.

I have the Haynes manual but it's not all that great for troubleshooting vacuum leaks.

Propane test next? Ideas?