I bought this Jeep 6 months ago. It has been idling rough since I bought it. It also takes a bit for it to start. Hold key for 5 seconds or so and it starts right up. It runs very rough until it warms up, then it just runs rough.

The motor only has 45k on a rebuild. Since I bought it I have replaced the cap, rotor, wires, and plugs. EGR valve has been removed and blanked off (it was faulty). Went through all of the vacuum lines, replacing any suspect lines. Pulled a vacuum on all components to verify they are holding a vacuum. I checked the CPS sensor, it is putting out correct resistance and voltage.

I'm open to suggestions. Thoughts?

 

Some more research suggests the O2 sensor may be shot. My research says the heating element can be tested, but the actual function of the sensor can not be tested without hooking a scan tool to the Jeep and observing the output of the sensor. Seems consensus is to replace it if in doubt. Found this one on Amazon: https://www.amazon.com/Bosch-12009-O...+12009+Titania. Other thoughts? I really am at a loss on trouble shooting this thing. I don't like to throw parts at the problem, but the O2 sensor seems like a maintenance item from what I gather.

 

Installed a new O2 sensor this morning and drove it to work and back. The idle, and acceleration are noticeably better. Still idling rough and some hesitation. Not sure where to go next. I've seen cruiser's website, I guess I'll start running down the list.

 

Fuel pressure tests.

 

How many of my Tips have you completed?

 

Only completed #7 so far. I replaced the fuel filter this morning as I didn't know the age/condition of the existing. Seemed to help it run better. After lunch I'll check the fuel pressure and flow rate. If that checks out, ground and connector refreshing is next on the list.

 

**Now sees the wisdom of Cruiser54's 'list**

by the way, 54 was my number in the fire department. They were always saying 'car 54 where are you'

 

1,3,4 and 5 need to be done.

 

I checked the fuel pressure and flow rate, they are within spec. Have not completed 1,3,4 and 5 from the list yet, got sidetracked with putting in a gauge cluster with gauges instead of idiot lights.

It is still idling rough, sometimes rougher than others. Something is still wacky. When it is running especially rough the RPMs drop. Below are two pictures of the Tach, as I am not sure what the numerical value is for the tick marks. The lower mark is when it runs rough.







What are the RPMs on each of the pictures? What RPM should it idle at in gear?

 

do the tips before screwing with anything else just yet!!

 

Ran through the list today. Completed the following:

1 – Ground refreshing
3 – Connector and relay/receptacle refreshing
5 – Checking sensor grounds
7 – CPS testing and adjusting
8 – TPS testing and adjusting
11 – Throttle body and IAC cleaning

I started the Jeep as I completed each item. Negligible improvement between items. I did 8 last. Before I completed 8 it started and idled good, then after running for 5-10 seconds it started to idle rough again. I assume it is in open loop at start up, then goes into closed loop and begins to run rough. Is that accurate?

Then I completed 8 and things got weird. The REFERENCE voltage is 4.88 volts, so 17% of that is .829 volts. Mine was reading .652 volts OUTPUT. I adjusted the TPS to read .829 volts OUTPUT. Started the Jeep and the idle shot up to 2500 RPMs and stayed there. Shut it off and adjusted the OUTPUT voltage to .750 volts, started Jeep, idle was normal. Adjusted the sensor with the Jeep running to the previous .829 volts OUTPUT voltage, idle didn't change much. Let it run for a while and the idle climbed to 1000 and stayed there, then after a few minutes up to 1200 and stayed there. Not sure what that indicates, perhaps the TPS is faulty?

Also, I am still not sure what the first two tick marks on the tach indicate. What are the RPM readings for those marks?

 

Probably a faulty TPS.

Ever replaced the oxygen sensor?

 

It has a new Bosch O2 sensor, one week old. Is there any way to test the TPS?

 

Yeah. With an analog voltmeter.
Have you ever replaced it?

 

No I haven't. What is the procedure with an analog voltmeter?

I did notice while setting the TPS, I lost the signal a couple times. At the time I thought the leads had lost contact with the wires in the connector. But now I am thinking perhaps the sensor stopped outputting a signal intermittently?