Rough idle, no codes
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gamefreakgc
Elite Member
I've had the ECU overadjust the idle and drop, only to come back up like you mentioned. Never happened again. Make sure your plugs and wires are good, maybe run some fuel injector cleaner if you want.
jreask
Member
How long since the plugs and wires have been changed? That is the first thing that I would suspect. I had the same problem and after changing plugs, wires, air filter I still had the problem. Tonight I tried the SeaFoam through the PCV tube. I used about a half of a can. Let it sit for 15 minutes and then took it out for a spirited ride. I had the RPM'S up near 5K a few times. There was some smoke, but no where near as much as some see. The idle has smoothed out and it seems a little peppier. I will see in the next few days if it stays smooth. It is still a little rough, but a tremendous improvement over what it was. What year is your truck? How many miles? IF you have a separate Idle Air Control it could be the culprit. We need more info to really determine what the causes might be.
JR
gamefreakgc
Elite Member
I second the idle air control valve under the throttle body. Might be gunked up or dirty if the idle drop is consistent. Will tend to act up more when the engine is nice and hot.
RunnerPDX
New member
I'm going through this right now -- http://www.toyota-4runner.org/3rd-g...e-[-beat-dead-horse]-need-some-direction.html
I've done EVERYTHING possible to shake this. Finally had a smoke test, small vacuum leak was uncovered with the lower intake manifold gasket, but not enough of a problem to throw a CEL.
I'm replacing the two gaskets this weekend and hope to hell it fixes it...
But I started with the TB, and IAC... couldn't agree more that's where to begin. Also clean the MAF.
I had this issue it ended up being my throttle position sensor. It's easy to test and easier to replace.
I could simply have the engine idling and tap on the sensor and it would go in and out of rough idle so it was obvious the sensor was it.
To test it properly though use a volt meter set for 12v DC and with the key on but engine NOT running place a sewing needle inside the connector at the bottom most wire (assuming you have the three wire TPS) to reach inside and connect your positive lead to it then connect your ground anywhere else. With the throttle closed you should be reading less than 1v then open the throttle fully it should increase linearly and smoothly to less than 5v (My readings on my old TPS would jump all over the place and not hold still yet I had no codes only occasional rough idle) my new readings are .547 closed and 3.781 open or close to that.
Good luck, hope that helps eliminate a possibility if nothing else.
I could simply have the engine idling and tap on the sensor and it would go in and out of rough idle so it was obvious the sensor was it.
To test it properly though use a volt meter set for 12v DC and with the key on but engine NOT running place a sewing needle inside the connector at the bottom most wire (assuming you have the three wire TPS) to reach inside and connect your positive lead to it then connect your ground anywhere else. With the throttle closed you should be reading less than 1v then open the throttle fully it should increase linearly and smoothly to less than 5v (My readings on my old TPS would jump all over the place and not hold still yet I had no codes only occasional rough idle) my new readings are .547 closed and 3.781 open or close to that.
Good luck, hope that helps eliminate a possibility if nothing else.
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