99 TJ.....engine issue on warm up

[birdo]

Greetings,

99 Jeep TJ 4.0 liter, 5-speed.

Starts up fine and settles into smooth idle. Under load as the engine warms, she coughs and sputters and surges for a couple of minutes and then settles down and runs just fine. No "check engine" lights...ever. As soon as the engine gets up to temp, everything is fine. If I let it cool down a few minutes,restart it, it does the same until it gets back up to temp.

I get the impression that this is occurring  while the injection system is in open loop mode.

So far I have:
Changed plugs, cap, rotor and wires.
Replaced Engine Coolant Temperature Sensor (CTS)
Replaced Air Temperature Sensor (ATS)
Cleaned Throttle Body
Cleaned Idle Air Controller (IAC)

Have ordered a MAP sensor.
Have checked for vacuum leaks.....throttle gasket, intake/exhaust gasket, injectors, crankcase ventilation. All is good.

Took it to a local dealer (big mistake) who said they couldn't find anything and I have my doubts that they did any checks at all. (coz they didn't charge me for it)

Any ideas.....I'd be willing to take it to a good mechanic who really knows Jeeps. Recommendations?

Cheers

[JackstandJohnny]

Jay at Chanda.......... aka lemon-aid Jay.......  he knows his stuff..............

[LEMON-AID JAY]

Give me a call tomorrow at the shop and will see what we can do for you. 403 287 3350

[birdo]

Took the beast in to see Jay today. He couldn't have been more helpful. Spent a very cold morning checking for vacuum leaks and ran the gizmo over the computer and everything came up trumps. Jay has suggested I replace the TPS and if it ever warms up, I'll put it in and see what happens. Watch this space.

[silverfox]

Took the beast in to see Jay today. He couldn't have been more helpful. Spent a very cold morning checking for vacuum leaks and ran the gizmo over the computer and everything came up trumps. Jay has suggested I replace the TPS and if it ever warms up, I'll put it in and see what happens. Watch this space.

Well hell, it was good to meet you today John, hopefully you get the ole girl straightened out....................she was probably just fumed at you for making her pull that pickup out of the snow bank.

I was the guy with the Mango Rubi that picked up the winch

[birdo]

Ok...replaced TPS.......no change...arrggghhhhh! This really has me stumped.

Ha,ha...I never did pull that guy out....if he had asked nicely I might have. His truck is still stuck. Could be until it thaws...or he eats some crow and apologizes. Common courtesy will get ya a lot further in this world than cussing and swearing.

[TJ Sparky]

  It could be your upstream O2 sensor between the Cat and the engine. Unplug it on cold start up and see if it fixes it.......if you have no rough idle on start up it needs to be replaced. Worked for me.

 

[BrokenAxle]

I was thinking O2 sensor too.  Good luck.

[birdo]

Worth a shot...I'll give it a try and let you know.

[birdo]

Just a footnote on this...rough idle is not really the issue.....the problem occurs shortly after engine start (or restart) when the normally smooth engine starts the misbehave. If I try to hold a steady RPM under partial throttle the engine will speed up then slide back then speed up and slide back.....almost rhythmically. Jay will testify to this. Then after 2-3 minutes, the engine settles down and idles and runs fine. If I try to drive it, it will buck no matter how much or how little throttle I give it. Eventually it will settle down and drive as per normal.

[birdo]

Now that the weather has settled down a bit, I got busy and replaced the intake/exhaust gasket. Same result I'm afraid. Now I'm baffled.

[raf2379]

did you check fuel pressure, compression/ leakdown test. Injectors? grounding? fuel pump? check all fuel pump connectors.

[JackstandJohnny]

did you replace that MAP?

mine does the same thing when i start it up in the morning.  it'll stutter an dstall out if i give it gas.  i have a stored MAP code but it doesn't throw a CEL.  i've learnt to live with it   after it runs for 30 seconds it goes away.  might be similar, maybe not? 

[Immortal]

Just throw as many parts at it that you can think of.




Probably just needs belt dressing.....

[BrokenAxle]

not everyone should fix jeeps like you do trevor!