Weird Idle Problem

[4Runner7]

Having a weird idle problem. Upon starting my '99 4Runner up and getting the engine warm after driving for approx 10 mins, my RPM's will start to go down from approx 650-700 to almost 550-500 and sound like it is going to die when the truck is in PARK. Truck runs great on the road and usually don't have any problems with it when it's in D, such as sitting at a light. Seems to only happen when I am in PARK and the engine is idling. My mech looked at the codes from the check engine light and it was giving him bad O2 sensor readings. Pulled the sensors and said that they were fine and didn't need replacing. We cleared the codes and off I went. Happened again and he still couldn't find out what was wrong. I think that he disabled the check engine light, if that is even possible, b/c it doesn't come on now when the problem occurs. Other than that, truck is running great. No problems. Any suggestions would be great. Thanks!

 

[RunninOnBlue]

Did you check the PCV?

 

[T4Life]

I had similar problems a while back, they disappeared when I replaced my plugs/wires with dual electrode plugs and cleaned throttle body.

 

[4Runner7]

Interesting about the spark plugs. That is the second time that someone suggested that. I had a tune up about 6-8 months ago, about when the problem started, and of course the spark plugs were changed. I am not sure which ones he used, as I went to a new mech.

So you changed the plugs and wires? Any specific place you got those???

I will have to check into the PCV as well. Good suggestion...

 

[T4Life]

Interesting about the spark plugs. That is the second time that someone suggested that. I had a tune up about 6-8 months ago, about when the problem started, and of course the spark plugs were changed. I am not sure which ones he used, as I went to a new mech.

So you changed the plugs and wires? Any specific place you got those???

I will have to check into the PCV as well. Good suggestion...

Well im in Canada so my parts stores are probably all different, just make sure their NGK dual electrode plugs, and dont bother with platinum ones.

Also I think that giving the throttle body a thorough cleaning did more for my idle issue than the plugs did. Make sure all of the carbon is cleaned out, and you could look into the IAC valve if your truck has it as well as the AFM.

 

[TheDurk]

If it runs great and after 10 minutes goes to crap, that means it works in open loop and and fails in closed loop. When the ECM goes into closed loop, it starts using the O2 sensor to set trim and timing. You are getting O2 sensor codes.

I'd ignore your genius mechanic and replace the front O2 sensor. How old is it, anyway? He LOOKED at them and decided they were fine? I'm not buying this part of the story. Which code was it, exactly? How did he test them?

Do the throttle body clean in any case. I had a closed loop only problem that was cured by this.

 

[dthaxton]

Having a weird idle problem. Upon starting my '99 4Runner up and getting the engine warm after driving for approx 10 mins, my RPM's will start to go down from approx 650-700 to almost 550-500 and sound like it is going to die when the truck is in PARK. Truck runs great on the road and usually don't have any problems with it when it's in D, such as sitting at a light. Seems to only happen when I am in PARK and the engine is idling. My mech looked at the codes from the check engine light and it was giving him bad O2 sensor readings. Pulled the sensors and said that they were fine and didn't need replacing. We cleared the codes and off I went. Happened again and he still couldn't find out what was wrong. I think that he disabled the check engine light, if that is even possible, b/c it doesn't come on now when the problem occurs. Other than that, truck is running great. No problems. Any suggestions would be great. Thanks!

A few months back I had a similar problem. All of a sudden it would start idling funny at a red light and when it was sitting in park. I took it to a Toyota Dealership and they thought it was plugs and wires so I had them replaced. 2 weeks later it started doing the same thing so I took it to a small mechanics shop in town and he said it could be a bad injector. So after he opened it up he found that injector 4 was bad. He got the part from a local parts store and replaced it for about 1/3 the price that the Toyota Dealership could have done it for... not to mention Toyota raped me for the plugs and wires.
The O2 censor is a good start along with the throttle body. If that doesn't work it seems plugs and wires may be fixing the problem for other folks. I would maybe mention the injector to a mechanic and see what he thinks about it. It worked for me.

 

[4Runner7]

I don't really know what codes that they were exactly, but I was kind of thinking the same thing. I think it's time to switch mechanics, b/c if that was the code that the computer kept throwing out, then it sounds like that's the problem! I will try the throttle body cleaning first to see how that does, then move onto the O2 sensor. Hopefully that isn't it b/c aren't they pretty expensive to fix? Any thoughts on that?

 

[KJ6SYK]

Need help

I had my head rebuilt, replaced spark plugs, spark plug wires, water pump, oil changed, oil filter, tranny gasket, exhaust manifold, exhaust manifold gasket, intake manifold gaskets, fuel filter.

After a couple of weeks my truck started to idle rough. Coming home from work my truck died exiting the off ramp. So I cleaned the tb, iac, maf. After doing that it still idles rough. I'm at a lost now. Any suggestions on what could be the problem? It's a 2.7 l with a little over 225,000 mi. I also replaced the egr valve and egr temperature pressure sensor.