Surging Idle

[Bansheemanche]

Ok at idle my MJ has alittle surge and was wondering what it might be. On the tach I installed the idle bounces between 700-500 RPM. Is my IAC going or what? This is on a 4.0L.

 

Thanks.

[maddzz1]

Does it happen when you first start it up or after it warms up or both?

It sounds like your IAC is sticking.

[Geonovast]

Both my Renix 4.0s did that a little bit. HO idles fine..from what I can hear anyway. No tach yet :( But the Chrystler 2.5 idles fine.

[135Boom]

You know I have replaced every sensor there is to replace on the MJ and mine, when cold the first few minutes does the exact same thing. Idles at 750, but dips down to 450-500 almost like the compressor for the a/c or defrost is kicking on, but it isnt. NEVER when warm, and NEVER after about 5 minutes of idle. Just does these dips in RPM a couple times and its gone.

Not to worried about it, but it is weird.

[Geonovast]

You know I have replaced every sensor there is to replace on the MJ and mine, when cold the first few minutes does the exact same thing. Idles at 750, but dips down to 450-500 almost like the compressor for the a/c or defrost is kicking on, but it isnt. NEVER when warm, and NEVER after about 5 minutes of idle. Just does these dips in RPM a couple times and its gone.

Not to worried about it, but it is weird.

 

That's because when the Renix system is cold, it doesn't use sensor input to run. It goes off of pre-set tables.

[BLHTAZ]

It's either IAC or TPS. Mine idles perfect and steady at 600 RPMs after initial start up. At start up it typically goes up to about 1500 right away and then moves back down to 600 in just 3-4 seconds.