northernnorm

Help please have a"99" sport 4.0 starts/idles fine after 1-3 min it starts to run rough almost stalls kinda chokes and coughs some backfires through intake. Get wooshing sound at air box like it is really tryng to suck air recovers then does it all again. It will do this for 5-7 min then smooth out and run fine no loss of power slight loss of mpg 1-3. Does this every time it sits for 10 min. If I try driving when it is doing this it will smooth out if I punch it up to 1800rpm or better. What I have done. Started with full tune up plugs,wires,cap,rotor,
air filter. Cleaned throttle body and idle air motor. Replaced temp sensor at first it only happend between 100-175 deg. Finally got ck eng light code said TPS replaced it. None of this has helped. Side note the colder it is outside the shorter the rough run time is. Sorry so long wanted to give all the info I could.

tjwalker

Are you still setting fresh codes for the TPS circuit, even after replacing it?

If so, you must concentrate on that circuit. There are other parts of the TPS circuit besides the sensor. Connector/wiring need a very close inspection here.

But follow the lead of the OBD system. It is definitely telling you something.....

northernnorm

No more codes. When I restarted it after getting the scan the ck eng light was off and hasn't come back on since. As a double ck I asked the tec if he had cleared the codes and he said no.

freegdr

un p[lug the iac motor when its doing this see what happens

northernnorm

I'll give that a try in the am and post results

northernnorm

Unpluged IAC while it was doing its thing and no change at all

jburg

Im having pretty much the exsact same problem i think, only difference is it dosent do it every time its kind of random but happens only when its off for a short amount of time and happens more while its hot out, also a 99 cherokee sport 4.0. I have so far changed the plugs, wires, rotor, MAP sensor, and i just shanged the coil today. I havent ran it yet but i will post if it helps tomorrow. Feel free to message me.

Bustedback

Could be the coolant temp sensor reading too cold causing the engine to run too rich once it warms up to operating temp. The coolant temp sensor won't always set a code, you need to use a scan tool and watch the real time data as the engine warms up to see if the CTS is changing as the temp increases.

Jakob

omg yes i have this same exact problem!! im still trying to figure out what it is

jburg

Drove the jeep with new coil and helped a bit but not the cure I don't think.

audirick

I have a 2001 automatic that I use to pull a trailer. After pulling the trailer loaded and go to restart the cherokee after a short period of time 10-20-30 min., it idles rough. In park or neutral I have to rev the engine quite high, as the rpms slowly rise I hear a knock or to and then it will run fine. Only did this after towing the loaded trailer until today with no trailer. I feel your pain.

VTJeep

o2 sensor, o2 sensor, o2 sensor...
i replaced my plugs, wires, cap, rotor, TPS, IAC, flushed gas lines, cleaned pump/filter assembly...
and it was all well and good cause overall all thoes new parts werent hurting anything but my wallet... but it all came down to the fact that it wouldnt throw a code... till finally, after about 5 months, the CEL came on and it said the o2 sensor wasnt functioning properly. 2 new, good, o2 sensors and she runs awesome. went from 11 mpg to 17 mpg!

northernnorm

Success at last was finaly able to get it scaned in real time as it was running bad and it showed the upstream o2 sensor was shorting out. Got lucky and the old one came out nice n easy hit it with the PB last nite then again this morning. Part was $60. Thanks to all of you who posted hope the others that are having similar probs get them figured out faster than I did (about 10 months)