So the other day I started my jeep and it ran like ****. At idle you can here it missing and running rough. But when I am driving it seems ok but a little sluggish because of the miss. So far I changed the wires cap and rotor also I pulled the plugs and they look fine no black anywhere and the gap was good. I also checked for vacuum leaks and couldn't find any. Today I poured seafoam in the gas tank because I thought the injectors might have corrosion in them but it didn't fix the problem. It runs a little smoother but its still missing. My jeep is a 95 xj sport and its not throwing any codes no check engine light. When I relocated the vac ball under the hood the vac hose cracked but I put tape on it and it has been fine. This also happened a couple months ago so I don't think its that. I would benefit from some peoples opinions on this so someone please help thanks guys.

 

First off, taping any vacuum line is bad news. Replace any suspect vacuum line. Always. Vacuum can easily sneak through tape! These are inexpensive fixes.

Not matter how your plugs looked, could still be an issue. Consider replacing them and if it doesn't resolve, you have an extra set. Go with Champion coppers gapped to .035

Ignition coil can be tested for primary and secondary resistances with a manual and a meter.

 

^this. And you also should test your throttle position sensor. This sensor is located on the throttle body. Also clean all grounds, etc. etc.

 

Yup, forgot about the TPS. Here is more on that...
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The throttle position sensor is connected to the throttle shaft on the throttle body. It sends throttle valve angle information to the PCM. The PCM uses this information to determine how much fuel the engine needs. The TPS is really just a simple potentiometer with one end connected to 5 volts from the PCM and the other to ground. A third wire is connected to the PCM. As you move the accelerator pedal with your foot, the output of the TPS changes. At a closed throttle position, the output of the TPS is low, about a half a volt. As the throttle valve opens, the output increases so that, at wide open throttle, the output voltage should be above 3.9 volts. Testing can be performed with an electrical meter. Analog meter is best. You are looking for a smooth sweep of voltage throughout the entire throttle band. While slowly opening and closing the throttle, take note to the movement of the voltmeter needle. There should be a direct relationship between the needle motion to the motion of the throttle. If at anytime the needle moves abruptly or inconsistently with the movement of the throttle, the TPS is bad

You should have 5 volts going into the TPS. At idle, TPS output voltage must be greater than 200 millivolts. At wide open throttle (WOT), TPS output voltage must be less than 4.8 volts.. The best is to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. One of the other wires should show .26V (or so). The other wire will be the ground and should show no voltage. Move the throttle and look for smooth meter response up to the 4.49 at WOT.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.

The TPS is sensitive to heat, moisture and vibration leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following: -

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics! It should be verified early in the troubleshooting process, when a transmission issue is suspected!

• Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".
• High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.
• Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.
• Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted acordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.
• Engine Misfire: A fault TPS can report values outside the deined acceptable range causing the ECU to incorrectly fuel the engine. This is noticable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessing misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.

 

Thanks a lot for the input guys. Today I found out that its running on 4 cylinders, 3 and 4 are not working. I checked the compression and 3 and 4 were about 50 and the rest were around 160. That is pretty bad compression could it be a head gasket blown?

 

Mine did exactly the same thing. Checked all you checked. For no reason, it started running fine after 1 week.

Flash

 

yea its weird i just started it one day last week and it started missing and its really bugging me. my motor does have 161,000 on it though

 

Absolutely. That is classic to have low compression on two adjacent cylinders with a blown head gasket.

 

Well today I found out its a blown head gasket ****