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Engine not idling and running correctly

Mudviper

NAXJA Forum User
Location
Fenton, Michigan
Seeking some assistance trying to figure out a problem with the XJ. A little background, I was going down the trail and the XJ and it start to lose power, then all of a sudden stalled. Had a bit of a hard time getting it restart, but managed to get it started again, but wouldn’t maintain idle. It wouldn’t start unless I opened up the throttle a little bit. If I put it into drive it would idle without any trouble. I was able to drive it back to a place I could work on it, but I had to ride the brake and maintain high RPMS otherwise it would stall out.

Thinking that it was the crank position sensor that was malfunctioning, I replaced it, but it made no difference at all. I cleaned out the throttle body, cleaned out the electrical connections and even switched out the battery, but no changes to how the engine performs.

What it is currently doing: At a cold start, the engine will start right up and idle without any issues, and will stay idling. Once I put it in gear and start to try and drive it, the XJ wants to stall unless I ride the brake and keep the RPMs up. If I let it stall and try to restart it, it would start, but will not idle and immediately stall out. If I give it a little throttle while starting it, it will start and the RPMs will race up then stall immediately. If I keep a little pressure on the throttle while is starts up, the RPMs will race up, then come down to 1000 RPMs then jump up again then come down to 1000 RPMs then jump up again. While it is doing this, I put the XJ into Drive and the idle smooths right out and runs as normal. If I let it idle in Drive for a few moments and then put it back into Park, it will remain to idle smoothly until I want to drive off, then stalls again. The engine light does not come on at all during all of this, so I don’t think it is recording any error codes. This is a 99 XJ btw

Anyone have an idea what to check for?

Thank you
 
You didn't mention if these symptoms are present when you do a cold start (you said it started right up and idled but not whether it stalled when you tried to drive it). If it works when cold and only stalls when it is warmed up I would check your O2 sensor. The O2 sensor takes over once you get into closed loop operation (engine warmed up) and is the only thing I can think of that would cause this issue only when it is warm.

I would also check your air filter as it kinda sounds like it is starving for oxygen.

HTH
Todd

Seeking some assistance trying to figure out a problem with the XJ. A little background, I was going down the trail and the XJ and it start to lose power, then all of a sudden stalled. Had a bit of a hard time getting it restart, but managed to get it started again, but wouldn’t maintain idle. It wouldn’t start unless I opened up the throttle a little bit. If I put it into drive it would idle without any trouble. I was able to drive it back to a place I could work on it, but I had to ride the brake and maintain high RPMS otherwise it would stall out.

Thinking that it was the crank position sensor that was malfunctioning, I replaced it, but it made no difference at all. I cleaned out the throttle body, cleaned out the electrical connections and even switched out the battery, but no changes to how the engine performs.

What it is currently doing: At a cold start, the engine will start right up and idle without any issues, and will stay idling. Once I put it in gear and start to try and drive it, the XJ wants to stall unless I ride the brake and keep the RPMs up. If I let it stall and try to restart it, it would start, but will not idle and immediately stall out. If I give it a little throttle while starting it, it will start and the RPMs will race up then stall immediately. If I keep a little pressure on the throttle while is starts up, the RPMs will race up, then come down to 1000 RPMs then jump up again then come down to 1000 RPMs then jump up again. While it is doing this, I put the XJ into Drive and the idle smooths right out and runs as normal. If I let it idle in Drive for a few moments and then put it back into Park, it will remain to idle smoothly until I want to drive off, then stalls again. The engine light does not come on at all during all of this, so I don’t think it is recording any error codes. This is a 99 XJ btw

Anyone have an idea what to check for?

Thank you
 
Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Do the same for the grounding wires from the starter to engine block, and from the battery and engine to the Jeep's frame/body. You must remove, scrape, and clean until shiny, the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds and the ECM/ECU may behave oddly until you remedy this.


The symptoms you noted are caused by low battery voltage. Inspect the under hood wires and wires connectors, especially at the engine computer, for damaged, dirty, corroded, or loose wires/wire connectors.

Inspect the ignition switch and make sure does not have any short circuits or open circuits. and that it functions smoothly and correctly.

It wouldn't hurt to test the battery, test the alternator, test the Throttle Position Sensor, and test the CPS.
 
You didn't mention if these symptoms are present when you do a cold start (you said it started right up and idled but not whether it stalled when you tried to drive it). If it works when cold and only stalls when it is warmed up I would check your O2 sensor. The O2 sensor takes over once you get into closed loop operation (engine warmed up) and is the only thing I can think of that would cause this issue only when it is warm.

I would also check your air filter as it kinda sounds like it is starving for oxygen.

HTH
Todd

Today when I tried to drive it at a cold start I maybe made it 500 feet then it wanted to stall. Restarted it, kept the RPMs up and drove it back to the garage. One of the first things I have check was the air cleaner. Had the problem in the past, everything is good there.
 
Today when I tried to drive it at a cold start I maybe made it 500 feet then it wanted to stall. Restarted it, kept the RPMs up and drove it back to the garage. One of the first things I have check was the air cleaner. Had the problem in the past, everything is good there.

In that case I would check your map sensor (be sure to check the vacuum line going to it for cracks or a break).

Do you have a fuel pressure gauge to check the pressure on your fuel rail?
 
I don't have a fuel pressure gage and I was going to get one, but didn't think it would be fuel pressure related since it idles and revs fine in drive and doesn't have a starting problem related to loss of fuel.

As for the map sensor, not sure how to check it, but when I did clean the throttle body up, I did clean up the map sensor and check the vacuum line and it looked good.
 
I don't have a fuel pressure gage and I was going to get one, but didn't think it would be fuel pressure related since it idles and revs fine in drive and doesn't have a starting problem related to loss of fuel.

As for the map sensor, not sure how to check it, but when I did clean the throttle body up, I did clean up the map sensor and check the vacuum line and it looked good.

I always check fuel pressure first but I agree it is probably not your problem area. I had an issue with rough start/backfire and stalling only to find it was low fuel pressure due to a hose coming loose in the tank so I have become a little paranoid :).

Great article on sensor tests in the attached

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

HTH
Todd
 
Still having big issues with trying to get the engine to run correctly. I have changed out the CPS and IAS sensors. I have changed out the TPS and the MAP sensors with ones that I borrowed from a friend, but still the engine will not idle correctly when it is in close loop. It will in Drive, which baffles me, but not in Park or Neutural
 
Time to throw in the towel, I can't figure this thing out. Tested all the sensors that may cause the problem, TPS, CPS, Cam Position, Coolant, and IAS but they all test out OK. No check engine light. Only thing I have not tried is to swich out the ECU. First time I have not been able to fix my own vehicle.
 
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