Low idle in drive

I've just noticed that my 2004 3.4L has started to idle lower than normal in Drive. Enough to make the dash hum and rattle, based on the tachometer, it appears to be around 600rpm. If I put it in Neutral it's fine, it's been wicked cold here lately and that's the only change.

It also seems to crank longer than normal after it's been sitting for a bit.

Plugs and wires are new OEM, air filter has about 15k on it. I have NOT cleaned the Throttle Body or Mass Air Flow Sensor.

I do have a small hole in my muffler though, would that be enough to change the backpressure and idle characteristics??

 

http://www.yotatech.com/f123/re-3-4l-v6-hard-start-hot-cleaned-iac-pics-92286/

 

thanks for the link, I'm having trouble opening the pictures, they appear as 'X's". I will search our site for IAC cleaning and see if there are any write ups. The warm hard start isn't terrible it just seems to crank a bit before it fires. I'm just hoping it's not bad injectors or something. thanks.

 

After looking around under the hood, I noticed my PCV hose was disconnected! How the Hell was it running as good as it was?

It's running way better, but occasionally I'm still dipping down in RPM's. Does anyone have an image of the IAC valve? I'm not seeing it under the hood.

 

Sorry no pic but the IAC is screwed onto the bottom of the throttle body...

 

If you go to clean out the throttle body it's right under there. Might have to do this myself as mine is idling rougher at red lights

 

^^ yours too huh..
I'll dig into it if it ever warms up..I still can't believe my PCV hose was disconnected!? It really wasn't running that bad considering how huge of a vaccum leak that was!

 

No real issues from a pcv being disconnected. Its just an emmissions thing, pulls vapors off the top end. You can remove it entirely if you wanted to, it wont affect how the engine runs as long as its allowed to vent. You might be a bit leen if youre wide open.

 

All it really does is take the exhaust gasses and puts them back into the engine to be burned for emissions. However it can make it run a little differently. The PCV is probably something I'll get to later lol. Mine is running rough because a while ago I made the mistake to wash my engine bay. Had gotten water in 2 cylinders. Got the water out but never replaced the spark plugs and wires after that. So I'll do that whenever I can and see if that fixes the issue

 

if you do delete it remember to put a filter on the valve cover fitting so it lets excess air pressure and gasses out, it will be filled with oil mist so you don't want it just going everywhere getting the whole engine covered in oil crud.

also the filter should be replaced for a new one at every oil change so it doesn't get oil soaked and start leaking oil

 

The IAC was removed when they went to the electronic throttle control system (ETCS). As my truck doesn't have it, I'm guessing, yours being a 2004, does not have it as well.

 

I'm going to hazard a guess that the missing PCV connection was causing a vacuum leak and the ECM may be a little out of whack. Might want to reset the ECM and see if it smooths out.

 

I was wondering about that, I couldn't find it at all! Rockauto does list it in their parts catalog though?

Yes! Another thing I was wondering, good call. It was so weird when I popped the hood and noticed it. It really wasn't running that bad, which leads me to think my ECM may have compensated for it. I'm going to unhook the battery and let it reset.

 

They may have still offered it on some of the V6s. My FSM has two different sections for the throttle body. The first section is for those with ETCS and makes no mention of the IAC valve. The second one is for throttle body w/o ETCS and shows the procedure for removing the IAC valve.

I know for sure mine does not have it. I cleaned the throttle body and found out I didn't need the IAC valve gasket. Also, when I did the supercharger, I followed the 4runner instructions (for engines with ETCS) and no mention was made of the IAC valve (as it was mentioned for the non-ETCS engines).

 

Interesting...it would be cool to find out what the cutoff point was, or the reason behind it. I really need to pick up a FSM!

 

Here is some FSM info http://web.archive.org/web/20101127014333/http://ncttora.com/fsm/1996/96_repair_searchable.pdf

and here http://www.customtacos.com/tech.old/files/05FSM/repair.html

I beleive 2004 Tacomas contain information from both fsm,s . Download em both before they disappear

I couldnt find a write up with pics at TW for the 3.4 .
If you plan to clean everything ,Pop some pics and write it up to help others

 

SOLVED - I just created this account only to reply to these threads. I have a 2013 4.0 with 188000, I ran into this issue in August 2021 and have been reading threads on this website since then. The Mass Air Flow sensor. My truck was idling around 550-600 rpm in drive and reverse. Neutral and park were normal idle RPM, after installing a

$86 Denso 197-6030 Mass Air Flow Sensor

Denso 197-6030 MAF my truck runs like brand new again. Amazon has these for around $60, the vehicle fit checker says it doesn't fit but it does, go with Denso, its closest to OEM. Good luck everyone!