WTGriffinJr

Vehicle: 1999 XJ Sport 4X4, 4.0, 5 SpeedManual Transmission.

Ok heres the debacle... My XJ is idling rough for the first few minutes of warming up. Once it has warmed up a bit everything is fine and it runs like a champ. CEL is on, but pulls no codes at all. Ive hooked up to several different code readers, at a mechanic not Auto Zone, and no codes come up, I plan next to take it to Jeep so they can charge me $115.00 for 15 minutes...

What I have done so far: New Distibutor Cap, New Rotary Button, New Spark Plugs, New Wires, New IAC, New TPS, Replaced the computer 6 months ago, New Battery 6 months ago, and New Alternator 9 months ago.

My last easy fix is to change the MAP Sensor.

Any Suggestions?

Parsnip

Have you checked resistance of the manifold air temp and coolant temp sensor? Can cause lean/rich conditions if the thermistor is not reading on the low end.

Turbo X_J

Have you performed a compression test? Were any of these components tested or just replaced? Can the scanner establish a link or not? Just throwing money at it usually won't fix it.

stoner22

Horn and cruise control work?

WTGriffinJr

Yes: The horn and Cruise Control both work...

Yes: All Code Readers are establishing a link with the vehicle.

I have no idea how to check the resistance of the Manifold Air Temp and Coolant Temp Sensor, or where they are located...

No: I have not done a compression test. Nor did I test the components before replacing them, I dont know how.

Basically I have to do as much work to my XJ as possible. Im a full time student with very little extra money to pay a mechanic. The Spark Plugs were do for a change anyway, the Distributor Cap and Rotary Button were original to the vehicle and Im surprised they even still worked considering their condition.

I bought this Jeep with 160,000 miles on it, it now has just over 223,000. Other than this rough idle everything about the Jeep is solid and running strong. The A/C doesnt work, it never has. I havent fixed it because I prefer to roll the windows anyways....

Turbo X_J

http://www.pacificcoastmanuals.com/1...ce_manual.html

67 GMC

I'd take it in and have them scan it. You've already put more than $115 into it for the parts that didn't fix the problem. A new MAP is over $50 and if that doesn't fix it, you're out more still. My bet is O2 sensor but you will find that out for sure if they scan it.

WTGriffinJr

Originally Posted by WTGriffinJr
Vehicle: 1999 XJ Sport 4X4, 4.0, 5 SpeedManual Transmission.

Ok heres the debacle... My XJ is idling rough for the first few minutes of warming up. Once it has warmed up a bit everything is fine and it runs like a champ. CEL is on, but pulls no codes at all. Ive hooked up to several different code readers, at a mechanic not Auto Zone, and no codes come up, I plan next to take it to Jeep so they can charge me $115.00 for 15 minutes...

What I have done so far: New Distibutor Cap, New Rotary Button, New Spark Plugs, New Wires, New IAC, New TPS, Replaced the computer 6 months ago, New Battery 6 months ago, and New Alternator 9 months ago.

My last easy fix is to change the MAP Sensor.

Any Suggestions?


So I took my Jeep in for a Diagnosis, we pulled a code for the EVAP Purge Solenoid. Which has been there for four years. Other than that the mechanic suggested changing the fuel pump since my fuel pressure was extremely weak.

So after spending $350.00 on having a new Fuel Pump installed, my Jeep is still bogging down during idling and needs about 10 minutes of warming up every time I start it to run well...

Overall the new Fuel Pump does make my Jeep perform a lot better. But this bogging down issue is driving me crazy. I also took off the Throttle Body and thoroughly cleaned it to point where it looks brand new.

When it bogs down, its goes to about 300 rpm's and then shoots up to about 1300. It will do this for several minutes, usually about 5, before it levels out to where its supposed to be and acts normal. It also makes a loud noise, like its sucking in as much air as it can get while it bogs down.

ehall

When the engine is cold, the computer uses default settings. It doesn't start using feedback loop until coolant sensor and O2 indicate that everything is warmed up. From what you describe it sounds like it is flooding out a bit, oversized injectors or oversized FPR or something like that. Could also be leaky injector that is flooding. Then when O2 comes online it shows rich mixture and the ECM cuts down the injector pulse width to trim.

Have you done any aftermarket performance mods in that category?

67 GMC

Is the EVAP Purge Solenoid ticking? I googled that and there is a lot of chatter on that front-Vacuum hoses, solenoids etc. May not be the issue but I can't stand having a CEL on.

WTGriffinJr

My XJ is bone stock, and the EVAP Purge is not ticking... I took it to a a different Mech yesterday and within an hour he called and told me he's getting another code for the TPS. Today he will be running some additional tests as well.

He is telling me that aftermarket TPS's do not function correctly most of the time. He is 'highly advising' me to use a genuine Mopar TPS. Is this true?

At this point im nearly $500.00 into trying to fix my issues, a genuine TPS will be another $109.00... Im tired of throwing money at it.

Parsnip

Yes, the molar tps is worth it

ehall

Only two brands I use for sensors are dealer and Standard

WTGriffinJr

I have a hard time believing this is just a TPS problem... I had to replace the TPS when I first got this XJ a long time ago now, and it wasn't running so bad then...

Is an actual Jeep Dealership Mechanic going to be able to find more than other Mechanics?

peep

My TPS behaves very badly when heat soaked in the summer. Not at start up but in very hot weather when all is fully up to temp. It behaves as it needs replacing, it has been replaced many times. The current one was bad in summer, yet all winter it has performed like a champ and the truck runs great. I'll see if it craps out again in the summer (then I'll put those vents in the hood. Current CPS is a Standard brand, have also used Echlin in the past. On an older TPS try cleaning the TPS pintle and the pintle seat in the throttle body, some contact or carb cleaner and your brother in laws tooth brush works well, brush gently, don't get rammy with the pintle. Often helps. Return toothbrush to brother in laws luggage when job is complete, thank him nest day at breakfast.
A scrub of the throttle body couldn't hurt also.