Originally Posted by 98jeepsrt6

Hey guys,
I seem to have a odd problem.. 98 4.0 i6. The jeep starts up fine, idles fine for about 45-60 secs and then she wants to fall her face but never does. If i give some gas as its happening the problem goes away. Wont happen again till next start up.

IMO it would seem to be around the time my system goes from open loop, to closed loop.(o2 sensor) Ive checked the ECU after warm up and my scanner shows my o2 sensor at closed loop.. Haven't checked prier to stumble yet though ill do that today. I do have a couple trouble codes but i dont think these would cause this problem. (1) VSS no output( No speedo gear) and (2) P0138 Downstream o2 sensor (Not installed because i don't have a muffler or cat, open down pipe, temporary)

Any ideas? Its not a big issue but i would like to solve it so i dont have to worry about it later on.

Another Question, Would my IAC cause this? During startup first 15-20 sec. it revs high (around 950) then slowly comes down to idle, about 20 secs after the idle set at around 750 it stumbles.


Upgrades:
Ford #19 injectors (yellow stick)
Pacesetter headers
Complete a/c Delete
Cruise Control Delete
New alternator
Big 3 wire upgrade
NO exhaust (Temporary)
Fuel Pump and Filter
Oil and filter (Both Engine and Trans)
Replaced Shift Solenoids


Cant remember anything else as of now...... Ideas??

Originally Posted by dukie564

sounds like an IAC issue. Clean and check the voltages.

Originally Posted by 98jeepsrt6

OK, ill do that. What voltage should i be looking at?? The IAC was cleaned when i replaced the exhuast mani. All throttle sensors and intake manifold were thoroughly cleaned. And i also replaced the TPS.

Originally Posted by 98jeepsrt6

Its a heated sensor, if thats makes any difference. But According to my factory gauge as well as my scanner the Temp Sensor reads normal at all times.. From cold start to operating temp.. I eliminated this factor due to correct coolant readings..


Heated oxygen sensors have an internal heater circuit that brings the sensor up to operating temperature more quickly than an unheated sensor. An oxygen sensor must be hot (about 600 to 650 degrees F) before it will generate a voltage signal. The hot exhaust from the engine will provide enough heat to bring an O2 sensor up to operating temperature, but it make take several minutes depending on ambient temperature, engine load and speed. During this time, the fuel feedback control system remains in "open loop" and does not use the O2 sensor signal to adjust the fuel mixture. This typically results in a rich fuel mixture, wasted fuel and higher emissions.
By adding an internal heater circuit to the oxygen sensor, voltage can be routed through the heater as soon as the engine starts to warm up the sensor. The heater element is a resistor that glows red hot when current passes through it. The heater will bring the sensor up to operating temperature within 20 to 60 seconds depending on the sensor, and also keep the oxygen sensor hot even when the engine is idling for a long period of time.

Originally Posted by xj87cherokee

mines doing the same thing mine was the map sensor it didnt throw a code till i unplugged it to clean it if you have the diagnostic scan tool that you can watch the voltage of sensors mine reads like .24 when its plugged up but if you unplug it ruff idle goes away it reads like .68