Help me out guys so I know where to start lookin.

When I start up the jeep for the first time in the morning it would start up just fine but rumble and shake back and forth for about 6-8 seconds then it idles out fine. The rpms are normal during this time. It's just a rough rocking-type shake. It only happens right after you start it up, almost like there's no oil and it's trying to run dry and something like a motor mount broke and the motor shaking loose. hard to explain but has anyone had this issue? Over the past couple of months I've noticed the idle at a stop sign or stop light has a very slight rumble every couple seconds too. It might be related. It only does this during the very first start after sitting for 1/2 day or so.


Thanks

 

Ya it sound like it just ur O2 sensor. There is nothing wrong with it, the sensor just need a few seconds to warm up
& get a proper reading of oxygen coming out of ur exost!!! Nothing to worry about unless it gets worse & more violent,
then I'd say it a comination of the O2 & ur motor mounts!

 

But we wouldn't be able to pinpoint which o2 sensor would we?

 

the first few seconds of start up
are controlled by the ecu the only sensor that it gets reading from
is the map sensor
the o2 could be bad also and giving off the wrong voltage on startup

it could be your IAC that is bad and needs a few seconds to settle in

check for codes

 

if its the o2 it would be the one before the cat

 

How do you check to see if they are operating properly?

 

http://dodgeram.org/tech/gas/Trouble/O2_sensor.htm
http://www.mr2.com/TEXT/O2_Sensor.html

 

I checked for codes and nothing. I wanna check the IAC. That's located on the throttle body right? It is not in my haynes manual for some reason. I went through the whole damn book. Is there another term for it that i'm missing?

I drove 20 min to my buddy's house today and when I parked it i noticed some white smoke coming from the engine bay. It was a very light smoke and only for a second or two. Came out of my hood vents. I can't say whether it's related to this or the exhaust wrap that I just wrapped over my snorkel hose. It says it may emit some smoke after the first couple uses but It's not wrapped on something hot so i don't think it's from that.

 

Sometimes called an Idle stepper motor.

 

Aha! That's in the book.

 

Here's my IAC:





What's a good way to clean that tip? Do you think it's bad enough to cause my idle issue?

 

when this was happening to my cherokee i replaced my o2 idle air control motor, and a couple other things...noticed when i changed my plugs they were a little wet. changed out my fuel injectors and it stopped completly.

the fuel injectors were letting the residule pressure from the fuel lines drip into the cylinders thus flooding my motor.


just how i fixed mine

 

This is on your 91 right?

I've always had the misfire in cyl 3 and recently got it in cyl 1. It hasn't showed it's ugly head in about a month though. This is pretty common with the 4.0 with the rail setup. (god i hate it!!)

 

I had a problem that was exactly as you described. One night my battery died. I had to get a jump start. When I did, there were a couple of people looking under the hood as it started. They said it looked like an electric light show with sparks jumping between all of the plug wires. I replaced the wires and the Cherokee ran perfectly and has since. BTW the old wires looked completely fine.

 

yup on my 91'.....had to throttle up to get it to go away....been fine for 6 months since replacing injectors