Hello Jeep experts....
I have a 2000 Jeep Wrangler w/ the 4.0 & automatic trans. That I traded for about 4 months ago. I have done some work myself and just had the cats replaced last week.
The problem that I have is before I replaced the cats, my engine has been stumbling/missing (around 35-45mph) while I hold that speed for a couple of seconds. I do not notice it when I am accelerating, just when I am holding at these speeds???? and yes it has done this since I have owned it
I don't know if it's a spark plugs/wires (I replaced when I first traded for it), intake air leak, fuel pump, trans, or a sensor (I replaced the ones w/ the new cats) or something that I have not thought of.
Throttle Position Sensor (TPS) is a potentiometer (variable resistor) that reports how far open the throttle is, to the computer. It converts electrical resistance (zero to 5,000 ohms scale) to a voltage signal that the computer interprets when setting ignition timing, fuel mixture and idle speed. It's mounted on the end of the throttle arm that's opposite where the throttle cable hooks up, and has 3 wires (5V, signal and ground). Webmaster note: this sensor tends to get "rough spots" in the middle and is tested by measuring its voltage as it is slowly moved up and down; sudden spikes or dropouts show a problem.
Mine began doing this as well recently. I had just changed the plugs and put a can of sea foam in. My gas mileage has skyrocketed though so I'm tempted to just wait until whatever it is just goes completely out. I'm a week and half in to a tank of gas as a daily driver in a wrangler. But I have that same stumble feeling right around 40 mph. It's fine under acceleration but at cruise it just seems to stumble in that range as well as at idle.
I also did the sea foam in the tank and the brake booster vacuum line. My Jeep is running a lot better except for this hip-cup. Replacing the cats. really helped smooth her out, but I wonder if I have a bad plug or wire??? I would think that I would notice this at start up and when its idling, not just at these speeds.
The one thing that is still not factory in her is a K&N air filter instead of the the OEM paper filter. I do not know if that is causing some issues.
I can get an TPS sensor (OEM of course) and see if that corrects it, but if its something as simple as replacing a plug, wire or a filter....hmmm
Okay, here we go. I can't believe that I did not notice this before, but when I was rechecking my plugs and wires I noticed that my throttle body was higher and upon closer examination I saw a spacer
I pulled the throttle body and cleaned it and my IAC which needed it badly. The problem is the guy before me put in a homemade spacer (I can't beleive that I missed this at first) I ordered a new gasket and should have it tomorrow.
I will bolt the cleaned throttle body and IAC back on (making it a stock configuration again) and see if that makes a difference. I have also replaced the K&N air filter too.
Hopefully the weather will hold, but where I am we are in for some heavy thundershowers.
Thanks again for all the responses, and I will post as soon as I can if the modifications resolved the issues or not.
Check what plugs are installed, some plugs do not work well in the 2000 and newer engines that no longer have a distributor. Good decision to get rid of the throttle body spacer and K&N air filter. No, let me rephrase that.... that was an excellent decision.
If your plugs look bad, here are three good plug choices... Autolite APP-985 (not AP985), Champion 7034, or Autolite XP-985. The first two are platinum tipped which will perform well for 100K miles, the iridium XP-985 will probably be the last plug you ever have to install in it as they really don't wear very much at all. A friend at Autolite pulled his iridiums at 165K miles and could detect no wear under the microscope.
__________________ When you have a choice, buy American.
I installed regular plugs in my Jeep, but I am going to pick-up a set of Autolite APP-985 (had to order them in) and switch them out.
My plan is to replace my head gasket tomorrow (had a leak so I thought I would do it too) along with removing the spacer. I hope to have the new plugs in by the end of the week, and switched out by the weekend.
Okay, I have replaced the valve cover gasket and put the throttle body back to factory. The Autolites will be in tomorrow (they said today, oh-well) and I will swap those out first thing. I will button everything back up and take her for a spin to see if she still has her hip-cup.
One good thing about all of this is that I have become strangely familiar with my new Jeep
I wanted to update folks about my journey with my stumbling problem. After replacing my spark plugs with new APP-985 my jeep was running great for a couple of weeks or a little longer.
It started up again when I was holding a constant speed anywhere from 35-45mph.
After rechecking about every sensor that I could think of, it finally dawned on me to check my coil pack, and guess what? I could see the number three plug/coil with a slight carbon trail, so I decided to replace it. I have not had any problems since with the stumbling
I just wanted people to know they might need to check their coil pack to see if there could be a problem. Remember my jeep never threw a code, so I was slowly hunting and pecking my way through this hiccup.