buckshot45

Not my 1st post, but it's been awhile and couldn't get into my old account.

I have a 1998 Tacoma 3.4 that was sitting for a couple of months. When I started it up it idled at about 1,000 rpm no CEL. Thinking it was just from sitting and that it would go away I just drove it. Well it started getting worse, idling about 1400 rpm. So cleaned the MAF and the throttle body and now it idles at 2,000 rpm. I thought it must be the IAC. Took the IAC off cleaned it and the throttle body put it back together, no change still idles at 2,000. I had a buddy of mine check it out with his Snap-On Solus Ultra scan tool. He tested everything and everything is within specs, not surprise because I still have no CEL. So I was still thinking it could be the IAC, so I blocked off the hole in the bottom of the throttle body and pinched off the vacuum line at the IAC. Started it and it idled about 700 rpm. Perfect I thought so I picked up a new IAC. Before replacing it I tested the old IAC side by side with the new IAC. To my surprise they function exactly the same. Put power to one side it opens all the way, put power to the other side it closes all the way. Now I am totally stumped, WTF!? I though for sure the IAC was bad. I have no other symptoms or driveability issues, just a ridiculously fast idle. I have no idea where to go from here.

Oh the truck has 198K on it and I have had it for about 10 years. This truck has had regular maintenance and runs great other than the fast idle.

donomite49

i'm thinking about eliminating the iac on my truck.
my old 22re did not idle up at all, i had to keep it running on cold starts.
that is the one thing that my 3.4 does that i do not like.

heres a thread that might help https://www.yotatech.com/forums/f2/m...-cured-258318/

paxam

sounds like a vacuum leak if the IAC is good and clean.
use a can of carb /choke cleaner spray it around the intake manifold or Throttle body . if the Idle changes then you found your leak.
remember that the carb cleaner will take off paint so be careful and be sure not to spray it on the exhaust ,it may flare up and cause a fire.

maachine

i agree. vacuum leak. trace that hose back that you pinched off. that's probably the culprit.

tantacoma

Sticking throttle cable?
Check the cable at the throttle. It should NOT be taut. Should be some play.

buckshot45

I should have said this in my original post. I have checked for vacuum leaks and could find not find one, I used nearly a whole can of carb clean looking. I have also checked the linkages and the butterflies are closing all the way, no hang ups there. Also nothing seems to effect the idle, have tried blipping the throttle, restarting, disconnecting the battery but none of these things have any effect.

What controls the IAC? The ECU? I am beginning to think that something is telling the IAC to increase the idle.

wyoming9

iTrader: (1)

Yes the ECM controls the IAC

The fact you have no codes is really strange .

unless you have not driven it enough to trip the MIL

Don`t forget there is the AC also sending a signal to the ECM to idle up the engine when the AC is on. If you have AC.

paxam

when you replaced the Iac did you use a new gasket? there may be a vac leak there.
the IAc is controlled the ecm, make sure your MAF(mass air flow sensor is good). you friend with the snap-on scanner can see the airflow. also if you remove it ,there is a small thin wire make sure it is not broken. to clean it I use electronic parts cleaner when it is cold(not ran) for about an hour. also look at the ECM for engine temp if the sender is broken it will try to keep a high Idle to bring the engine up to operating temperature.

buckshot45

I have put a couple hundred miles on the truck since this idle issue started. So if it was going to trip the MIL it would have done it by now. It does have AC, the idle does change slightly when turning it on or off.

I cleaned the MAF with MAF cleaner, and beyond that I had a buddy who had a new MAF they we tried on my truck and it made no difference so I put my old one back on. Yes, I used a new gasket on the IAC and the TB. I don't recall what GPM the MAF was showing but it was within spec. The temp sensor reads about 165-170 degrees, so I don't think that is it either.

What gets me is why when I blocked off the IAC, basically eliminating it, the idle dropped to 700? When I removed the IAC and tested it, it works perfectly. To me that points to the IAC. If it was another issue I wouldn't the high idle still be present even with the IAC blocked off? I have tried just unplugging the IAC and it does idle down to 1000 rpm or so but runs like crap and if you drive it that way it kinda lurches. With it plugged in and blocked off it seems to run great.

This thing is frustrating me like crazy!

rworegon

buck, the 65-70 degrees is the intake temp the MAF is reading, correct? The temp paxam is referring to in post 8 is the engine operating temperature that the ECM is seeing via its sensor mounted on the top on the intake under the fuel rail crossover pipe. Normal engine operating temp for the 5vz-fe is 176-203f per the FSM.

rworegon

Also, give the intake flexible tube a good inspection. I've had it get small cracks on the bottom side up in the fins. Air filter is clean?

donomite49

i did this to fix my problem
first i unplugged my ecu to reset.
i removed the throttle body and adjusted the throttle stop adjusting screw by exactly one eighth of a turn to close the butterfly a little bit more than the stock factory setting.
on the other side of the throttle body is a vacuum plunger with another factory set adjusting screw, i turned this screw out one half turn.
i put a 2.5 mm allen wrench on the screw to determine position first,
then loosened the 8 mm locknut (these are set with a locking agent from the factory) and reajusted the screws a set amount so they could be returned to the original settings.

buckshot45

oops typo. I meant 165-170 degrees. No I was refering to the temp the EMC is reading not the MAF. My temp on the scan tool when warm is around 170.


rworegon if you are correct this could be my issue. I questioned this early on myself but had two different people tell me that the 5vz-fe should have a 170 thermostat and so a temp reading of 170 seemed about right. If this engine is supposed to run at 191-203 this may be the issue. I will look more into this. and I will giver a closer look the the air intake hose. Yes, the filter is clean.

rworegon

Use the FSM link in my sig line to download yourself a copy of the FSM.

Actually, I made a mistake on the coolant temp range its 176-203f per FSM with many of us running right around 190-191f with the stock 82c (179.6f) thermostat.

rworegon

While you seem to be running too cool, here is a thread on high temp getting back to more normal.

Stock is a 82c (179.6f) deg thermostat on the 5vf-fe.

Pick up a thermometer that goes to 200+f, remove the radiator cap with the engine cold, start the engine and measure the coolant temp when the temp gauge (it uses a different sensor then the ECM temp sensor) is in its normal warmed up position and coolant is flowing through the radiator.

Your thermostat may be stuck wide open.

buckshot45

rworegon I checked for leaks in the air intake hose and found none. I ran the truck with a thermometer in the radiator and the temp matches what the ECT shows on my scan tool, although I could not get it over 167 degrees and that's with it idling at 1800-2000 rpm and it's about 84 outside.

Thanks for the link to the FSM I have been looking for one of those. That will help with this issue and many others in years to come.

rworegon

Sounds like the t-stat may be stuck open or it has a low temp t-stat installed. Has the rig overheated at all recently that may have caused the t-stat to stick open?

buckshot45

No it has never overheated. But it is still the original factory installed thermostat, so it is very possible that it is stuck open. Either way with it's age and mileage it not going to hurt putting a new one in there.

rworegon

Yes, pick up a 82c t-stat and gasket from your Toyota dealer, a gallon of Toyota Red coolant and some gallons of distilled water for a good system flush if its been awhile since the last flush.

Remember, install the t-stat with the jiggle valve down in the 6 o'clock position.

buckshot45

rworegon, you nailed it! I changed the t-stat tonight and the idle came right down to where it should be. Thank you for all the help on this one, I really appreciate it!