Wj falling on its face at red lights

98_tj

98_tj

under water
Joined
Feb 7, 2014
A friend of mine has a 2001 jeep grand Cherokee 4.0 with 250k miles, we just bought it for cheap and wondering why it falls on its face at red lights. We have changed the crank position sensor, and cleaned the throttle body. It is a cheap daily driver so we dont want to keep throwing money at it to try and fix it that way.
 
Use a scanner and see what the tps is reading.
 
Also check the MAP sensor and all wiring and hoses connected to it.

If you have a good meter then check the Flux capacitor, you will have to jack the truck up and get it to 88mph..........
 
Check MAP and TPS. I just replaced (last week in my neighbors driveway) a MAP on a 2001 Durango 4.7 with the same symptom, and I remember from RockAuto that the 2001 Grand Cherokee is the same Mopar MAP part number. It's about $45-60 depending on the part brand. It was throwing a "MAP sensor voltage high" fault.

But, it's a 2001 so it's OBD2, so you should check the codes to see what they say.

Check the codes!!!!
 
FYI, my neighbor took it to O'Reilly to get it scanned, and they gave him a printout of the troubleshooting flow and possible causes for that MAP fault code. I was really impressed and had never seen that before.
All of the troubleshooting instructions and explanations were spot-on for the standard logic of MAP sensor testing, so it was really nice to use it to help teach him how to troubleshoot.
 
Codes were:
Speed sensors f/r failed
Cluster malfunction (probably oil pressure guage)
Crank position sensor failed (just replaced)
Low oil pressure (oil hadn't been changed in God knows how long)
And stayed cold to long ( didnt have a thermostat)
 
Its a $500 car, runs perfect when driving down the street. Just not when stopped at a red light
 
Sounds like the Idle Air Control Valve is not opening up, therefore the engine suffocates and has no air intake when you stop and are at idle. That can mean the TPS sensor is bad, or the IAC is bad. Similar thing happened to mine years ago. I know I also changed the Crank position sensor out too, but not sure if it was at the same time.
 
VortecJeep said:
Sounds like the Idle Air Control Valve is not opening up, therefore the engine suffocates and has no air intake when you stop and are at idle. That can mean the TPS sensor is bad, or the IAC is bad. Similar thing happened to mine years ago. I know I also changed the Crank position sensor out too, but not sure if it was at the same time.
Click to expand...

As I was reading down the thread that is where my mind was going as well. IAC or a bad vacuum leak somewhere.
 
Also common for the upstream O2 sensor to read out of range and cause idle issues. How bad is the exhaust manifold leaking (because we all know it is), can fool the O2 if too little exhaust is passing it.
 
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