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I just bought a 1997 Toyota 4runner 3.4l and it has a high idle when the engine is cold.(1,500rpms) it is (1,000rpms) when the engine is at operating temp. I couldnt find a vacume leak. so I replaced the idle control valve and now it idles at (1,500rpms) when cold but at (700rpms) when warm. What do i do? Thanks! love the videos Eric! Keep up the good work!
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The IAC could be gummed up.
Restricting flow through the intake.*Edit*
Eric has a great video about diagnosing honda idle problems. This information can be used on other engines as well, just won’t be the same location and such.Like I said I replaced the idle control valve which is the same as the IAC and it doesn’t have a fast idle valve.
Two things..
Has the MAF been cleaned? May want to look at that. Try disconnecting the MAF and running it. You will get an error code, but see if it idles more normally.
Second, a vacuum leak somewhere. Hook up a scan tool and look at your STFT numbers if they are a -10 to -20 at idle and the number goes up (to say -1) or even positive when you Rev the engine, chances are you have a vacuum leak somewhere..
I would if you can look at the fuel trims numbers like the o2’s and see if they point you in some direction… like the car is rich or lean and its compisating for it… that would be an indicator of a vacuum or some air sensor probelsms
Thanks yall for your time. my STFT numbers where -13 at idle when I reved the engine they droped as low as -1 then jumped back up to around -7 and was kinda going haywire. one the engine got warmer my numbers where -7 at idle of 1,000 rpms. then when I reved it would drop to -1. Both times when I let off the accelerator it would drop to 0. I forgot to mention that a month ago it was doing the same thing and I got a check engine light when I was driving down the road. I looked at the code and it was one of my O2 sensors telling me the system was lean I cleaned the MAF sensor and erased the code saw the code 1 week later and I erased it. haven’t seen it sense.
If it was a vacuum leak why would it smooth out when the engine is warm? and if it was a sensor problem why would I not have a check engine light now?
[quote=”4runnerguy” post=174067]If it was a vacuum leak why would it smooth out when the engine is warm? and if it was a sensor problem why would I not have a check engine light now?[/quote]
The engine management strategies change when the engine is in open loop (cool engine) and closed loop (warm engine). There are many situations that only manifest in one condition or the other, so the absence of a symptom in one condition or the other is a clue but not an indicator. The reason you aren’t getting a code is probably because the computer is able to compensate within its adjustment range, but just because it can compensate doesn’t mean it can smooth out the symptom. The normal idle speed should be something ~750RPM, The neg STFT means the computer is restricting fuel which could indicate a leaking fuel injector (the computer is trying to decrease the amount of fuel to try to maintain 14.7:1 stoich). As the engine load changes, the fuel requirements change, and as the engine demands more fuel for its increasing load, the STFT will become less negative, perhaps even crossing 0 and becoming positive, if the situation requires it. Interestingly, faulty evaporative emission systems and exhaust leaks can cause a similar condition.thanks all yall for your help! I just got a check engine light when I went to go start my truck and they are P0100 maf sensor malfunction, and P0110 iat sensor malfunction. my question now is do those codes have anything to do with each other? and where is the iat located I think it is on the maf sensor..
I believe the IAT is part of the MAF on your model. If it isn’t, there should be a small round rubber grommet on the airbox where underneath that grommet is the IAT.
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