High idle.

[Broaner]

I've been reading through this subforum but can't seem to find a thread with the exact same symptoms.

My 4.0 has 125K on it. It cold starts just fine but almost always settles to a high idle. Right around 1500rpm. On occasion it will idle at 1800rpm. Clutching in slightly to put a load on it will drop the idle back down to 900'ish if I do it right. But the next time I come to a light it will idle again at that high 1500. So far I replaced the IACV.

This started when I replaced the vacum line going to the charcoal cannister. Do I need to recalibrate that sensor after diconnecting the vacum to it? I have reset the ecu and the only code that comes up is "General Emissions" or some BS like that. Also, I'm getting pispoor fuel econ. So its probably running pig rich and thus causing the high idle but why?

Also, idling for extended periods(5+ minutes) will drop it to a super low stumbling idle. On occasion it can't recover from the stumble and will die. But the truck has done this little nuance since I got it over 30K ago. It never bothered me because I still got good fuel econ.

 

[Danyokim77]

I have a simular prob with my 95 4.0L Ranger. But mine happened after I put a cold air intake on. I think it might have something to do with the rubber hose coming from the valve cover back into the intake tube just after the MAF sensor. I have yet to fix my problem, so I'm just guessing here.

I read somewhere on here that this rubber hose uses the hot air from your engine to prevent your throttle body from freezing up at start-up. I didn't know this at the time, and stupidly just clamped a small breather filter on it because the stock hose was too short to go back into my new cold air intake pipe. Ever since doing this, on cold starts it barely holds an idle and sometimes dies. But then once it warms up it idles way too high, like around 2000+ rpm. VERY annoying.

This weekend I am going to buy a new cone filter and throw away the one I have on there now because I think the filter oil is messing up the reading on my MAF sensor. Then I'll clean the MAF sensor with MAF cleaner, and then re-install the rubber line from the cold air intake to the valve cover. I hope it works. It was running just fine before.

I know some people say the cold air intake doesn't do much, but I don't care. I like the deeper sound it gives off. Works well with my Flowmaster 40 series. I'll let you know if my weekend fix solves any of these problems.

 

[spdcrazy]

i'm having the exact same thing happen to my 2.9. its got a new engine and everything ran fine untill one day i had a heater hose with a pin hole in it. she got hot but only 215ish. so i shut her down and fixed the prob, added coolant. and now its fine except for a high idle.

she also stumbles all over herself when she idles for a bit. my mechanic put the new engine in and he says he removed the emission stuff. but if worked fine for about the first thousand miles. so idk i'll just start messing with plugs and things and see what comes i guess.