Rough Idle and NO CEL

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Apr 30, 2009
Atlanta, GA
I have no one else to turn too! I wanted to get the forums input on a 99 Toyota 4runner (V6 - 112K miles) I have. I know its not a cruiser, but I figure the principal should be similiar.

The 4runner as been idiling very rough lately. RPMs do not drop or spike and the truck does not stall. Just idles very rough. The truck is stock. I have changed the MAF sensor and fuel filter in the past 3 years. I tried new denso plugs and wires with no improvement. The truck drives fine and there is NO "check engine light" A local mechanic said he thinks it is the idle air control valve. I though that might be a problem only if the RPM's were spiking. If you listen to the exhaust, it sounds like a big block V8 idiling, not a 3.4 V6. Please let me know of any ideas!

MAF sensor was replaced in 2007 with a factory one. Have not cleaned it. I use a stock paper filter not an oil based air filter. Whats's the link with the coolant? Levels are fine, but I am curious. It feels like the engine is going to stall, but there is no drop in rpm's. I don't think its the engine mounts. When you listen to the engine run, it sounds very sick. almost like a V twin bike or something like that. I am starting to notice a loss of power when driving around town. It has to down shift more often and the power just isnt there. I wish the check engine light would come on so I would have a clue where to start. Any thoughts on IAC, EGR? Thanks for any help.
Having air pockets in cooling system can cause some idle and driveablility issues as it interacts with the ECU via the temp sensor. Also the 22RE will have the quality of the idle compromised by a low coolant level. (Don't know if it's as big an issue on 5VZ)

It's strange that the idle wouldn't drop off though......

I would start with the MAF cleaning link above. (I think this is going to be the issue)

Might think about testing the MAF and the coolant temp sensor for function, electronics can be off enough to make it run bad but not set off the check engine light.

1996 to 2002 Toyota 4Runner OEM Repair and Wiring Manuals

I would also replace the PCV valve and maybe the fuel filter.

The check engine light isn't burned out is it?
Does it come on when you turn on the key?
thanks for the info. i replaced the fuel filter at 90K miles. the coolant is at a normal level. the MAS was also replaced around 100K miles with a new toyota one. could it possible be one of the coil packs or a bad injector? i wish the CEL would come on!
Bump for an update! :)
PLEASE let me know if you ever figured this out.
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I did finally figure it out. TIMING BELT!!! My truck had a very small water pump leak that caused coolant to drip into the timing belt area. Over time, the coolant hardened and created small rock like formations within the timing belt cover. The hardened coolant "rocks" got in between the cam and crank shaft gears and caused the belt to skip a few timing was way off according to my friend who is also a toyo mechanic. I think by around 11 degrees or something like that. We cleaned everything out, replaced the water pump and gasket (water pump was fine but did it since we were in there), and replace the timing belt. I never had a CEL come on and there never were any codes.

WOW what a difference. No more rough idle. The acceleration was drastically different. It felt like a new truck. That will be the last time that I don't change the timing belt and inspect water pump when scheduled.

We first looked at MAF, which I already changed and then vacuum friend wanted to replace the idle air control, but we didn't. Replaced fuel filter. None of those things changed my problem. It was the timing. I can't emphasize enough how much better the truck runs. Sounds healthier too.

To finish the story, we bought a new house and my 4runner was my extra car and paid off, so I sold it to help purchase our new house. I regret it and wish I still had her.

I hope this helps and good luck...if you can check your timing first that might help. Let us know how everything turns out.

Well glad you found the problem. Who would have thought that hey! I have never had a belt in my hand..I would have thought that to skip a cog would put it out more than a few degrees..another lesson here so thanks. Grab the timing light and see where it is at before jumping to a conclusion...
Hope the house is working out well...sorry to hear about losing the Runner
Thank you Justin!! I appreciate it! :)
I'll be scheduling a weekend to pull her into the garage and take a look. I was just about to throw crap-tons of parts at this thing, but I'll hold off until I check timing. :)

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