renix idling issues

[cheapcherokee93]

so my 88 mj, while now running okay is now having some idle issues. upon start up, sometimes it will jump to 2500 rpm and stay there for a couple seconds until it starts to go down to normal. i know this is bad because there is no oil pressure at start up so its wearing out my engine faster. it only does this on occasion but i still don't like it. second problem, after driving it and getting it warmed up, it mostly likes to idle a little bit high. high as in around 750 rpm in D and if i put it in Neutral 1000. i know it shouldn't be idling this high. sometimes it will bring itself down to normal level of about 750 in N and maybe 500-600 in D. i have read that cleaning the IAC is supposed to help so i cleaned it and at first it seemed like it was idling better but soon after it went back to its bad habits. i've read multiple threads on renix idle issues but they seem to say different things and explain different problems. so, any thoughts on what might be causing this? could my IAC just be bad altogether?

 

[bcmaxx]

Start with the basics, test the tps with a multimeter, clean or replace the iac, clean the throttle body plate.

 

[magimerlin]

When it idles high open you hood and wiggle the 4 relays on the pass side that are in a row. One of them is the +B latch relay (cant remember which is which right now)which helps control your IAC motor. I have the same issue on my 89 and that will fix it every time. I am just to lazy and usually do motte ember to get a new relay when at the parts house

 

[Super mud]

Thats pretty much it: IAC TPS and bad grounds. I've had a brand new tps take a dump and cause my high idle but chronicly not upon start up. So it could be the grounds are dirty. Sometimes after i pressure wash the engine bay or it's rained an ass load it will do it so I think moisture is affecting something somewhere maybe the IAC plug which has close terminals and can collect water. Good luck it's a bitch and theres a thread called the renix files with like 30 pages on this stuff.

 

[cruiser54]

What kind of oil filter do you have on your Jeep? Is it orange?
PM me your emai address and I'll send you a simple TPS adjusting/diagnosing procedure along with a simple test of your sensor ground circuit. You have a multimeter, right?

 

[cheapcherokee93]

thanks for the input guys.... and no i don't have an orange filter of death LOL

PM sent, cruiser54

 

[cruiser54]

thanks for the input guys.... and no i don't have an orange filter of death LOL

PM sent, cruiser54

Glad to see you're well informed on oil filters!!

Email sent.

 

[Ecomike]

A bad IAT (Intake Air temperature sensor) can also cause a high idle, as well as an intake manifold leak that changes the size of the leak as the engine warms up.

Grounds must all be less than 1 ohm from the sensors to the negative battery post. ALL of THEM!

TPS must not be worn out (requires and analog volt/ohm meter to test that), TPS must also be calibrated. Input voltage from the ECU must be steady, and constant (C-101 or other poor connector joints can cause it to jump).

There can not be any vacuum leaks!

O2 sensor must be working properly, and the O2 sensor internal heater must be getting 12-14 volts or it will cause odd idle speeds.

 

[cheapcherokee93]

well update....i did the fix that cruiser54 sent me....calibrated the TPS and fixed having over 1 ohm of resistance....still having the same odd issues. looks like i'll be trying out more stuff that Ecomike stated. i've also cleaned all the grounds to the body to ensure good connections.

I'm finding that it usually idles fine cold but once you drive it and it warms up it'll want to be around 1000 rpm in park/neutral. it also still does the occasional high idle upon start up but its totally random.

 

[043500]

I didn't see it mentioned yet but check the O2 sensor.

 

[Explorer 1]

Ask me tonight, I had a simular problem a few years ago, the guys at K & D told me how to fix it.

Thanks,
Fred
Explorer 1

 

[cruiser54]

If the O2 sensor has more than 80K on it, I would replace it. They don't always fail completely but can also become "lazy".

 

[cheapcherokee93]

thanks guys. looks like i will be replacing the O2 sensor then, probably wouldn't hurt to anyway.

 

[4x4xj89]

Guys I am having high idle issues but a bit different from what the OP described.

On occassion, the Jeep starts with high idle, it can be any where from 1200 RPM to 2800 RPM and stays there unless I shut it off and restart. On most occassions it goes back to normal but every now and than I have to restart it more than once to get it to idle normal. Not every start it does this, many days it just idles normal and next thing you know it does it!

Jeep is 89 with Auto AW4 and 4.0L and has 110K miles on it.

 

[b5blue]

I had an intermittent high idle problem, I replaced the IAC and the vacuum harness set, both sides (From NAPA.) and that cleared that up, the tubing set replacement helped generally all over quite a bit. (Even got a speeding ticket I still can't believe!)