Increased idle and speed

Stoney126

Stoney126

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Apr 1, 2021
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So a part two of sorts. My 2004 jeep lj with an automatic non rubicon. So my issue is this. No codes on the jeep pending or active. The jeep will accelerate slightly to about 1k rpms in forward or reverse after about three seconds of movement. And its always three seconds and the jeep has to be moving and in drive or reverse.

Things checked so far. Can be seen here Post in thread 'Another idle question' https://wranglertjforum.com/threads/another-idle-question.57129/post-1020942

My idle is fine though a little high at 700 ish rpm but not insane. I replaced the Iac with a new mopar piece and no change. I figured it wouldn't but though what the hell. I unplugged the Iac and the jeep no longer accelerates on its own. It also didn't throw a code either.

So I'm wondering what the pcm is seeing to command the iac to increase air flow. Im also wondering if there is torque converter clutch solenoid or something of that nature that may be coming on early and shutting off to early. When coming to a stop the rpms resist going to idle till at almost a complete stop.

At this point I'm not sure what to look at to repair.
 
maybe a vacuum leak then? I've had very little problems in this space, so I'm really. just guessing. But vacuum can definitely affect idle.
 
Ya I've checked vacuum and it holds pretty steady. The fact it doesn't do it with the iac unplugged also rules it out. Very strange issue for sure.
 
Yup. Got jeep warmed up let get to idle. Un plugged iac and it will not raise the rpm and raise speed. Problem goes away. It did this before as well so I though well maybe bad iac . Unfortunately not the case
 
Stoney126 said:
Yup. Got jeep warmed up let get to idle. Un plugged iac and it will not raise the rpm and raise speed. Problem goes away. It did this before as well so I though well maybe bad iac . Unfortunately not the case
Click to expand...

Maybe I'm not understanding, but if you unplug the IAC and the symptoms go away, it seems like you've more or less isolated the cause. It might not be the IAC itself; cleaning out the throttle body & that little air channel, and really that whole area. There's an IAC cleaning writeup that is probably something every jeep on this forum would benefit from regardless.
 
That's all been done. Actually removed and cleaned everything witha tooth brush.

With it being right at 3 seconds im thinking a load is being applied or requested.

The iac compensates smoothly for the ac compressor being applied and disengaged
 
Stoney126 said:
So a part two of sorts. My 2004 jeep lj with an automatic non rubicon. So my issue is this. No codes on the jeep pending or active. The jeep will accelerate slightly to about 1k rpms in forward or reverse after about three seconds of movement. And its always three seconds and the jeep has to be moving and in drive or reverse.

Things checked so far. Can be seen here Post in thread 'Another idle question' https://wranglertjforum.com/threads/another-idle-question.57129/post-1020942

My idle is fine though a little high at 700 ish rpm but not insane. I replaced the Iac with a new mopar piece and no change. I figured it wouldn't but though what the hell. I unplugged the Iac and the jeep no longer accelerates on its own. It also didn't throw a code either.

So I'm wondering what the pcm is seeing to command the iac to increase air flow. Im also wondering if there is torque converter clutch solenoid or something of that nature that may be coming on early and shutting off to early. When coming to a stop the rpms resist going to idle till at almost a complete stop.

At this point I'm not sure what to look at to repair.
Click to expand...
We had an incident a couple years ago...the engine began racing...the rpms crazy high...so much that at a stop light we shut off the motor..got to the campground...next day lifted the lid and found that the vacuum tube came loose. Put it back on...got a new tube ...problem solved...
 
Also this isn't issue when jeep is cold. Starts once its warmed up. Haven't verified the temp it starts at or if it starts when the jeep goes into closed loop.
 
Is the heater or defroster on? IIRC, the computer ought to bump the idle up a bit when it sees a request for the a/c compressor to come on.
 
Just as a side note as I went through something somewhat similar myself. After replacing an IAC Valve, it is neccissary to drive the jeep at 40MPH or faster, non stop consistently for 5 min in order to get IAC Vavle to find its origin and reset itself. This will happen AFTER you go for a drive and then shut the engine off and then restart the engine.
 
Well I've driven it several times on the highway and no problems in that area. But will try and do a reset and do a road test and do a shut off and restart
 
Don’t mean to dig up an old post but have you ever figured this out? I too have an LJ that is currently doing the same exact thing
 
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