Rough Idle really annoying !!! HELP

Pharaoh XJ · May 27, 2009

Hi guys, I ve tried everything this time & its really getting on my nerves, its my DD & I cant get nowhere.

Here is how it began; had to replace my freeze plugs so took off Intake/exhaust manifolds for the job.

After that it started idling really rough ( low) so replaced my intake gasket as I suspected a vacuum leak. Fixed it for 2 drives then went back.

Got some Carb cleaner sprayed on every possible location: Injector O-rings, manifold gasket, throttle body gasket & Butterfly pin.

Even got some scenting sticks ( smoke source) to check for any vacuum leaks.

Finally replaced my IAC fixed it for 2 more drives but was minimally idling, then went back to how it was.

Usually it fixes it self as soon as it reaches operating temperature & gets really bad & stalled couple of times under heavy load like: full steering lock & when in gear against the curb.

More info:
No codes
Defroster is acting up with AC on ( vacuum leak)
Exhaust manifold cracked

Please guys I am really pissed off & wasted a hell lot of time & money trying to figure it out.

Thanks

joe_peters · May 27, 2009

So, your profile says 1994.

What engine?

You say it is only a problem when cold, and that after it warms up it idles normal? It might be a leaking injector is causing a problem, allowing fuel to accumulate in the cylinder overnight?

Pharaoh XJ · May 27, 2009

Sorry forgot to say
1994 6 cyl AW4 155k miles.

It starts fine idles for 10 secs then starts the low idle: revs drop then suddenly surges, drop again then surge back, etc

joe_peters · May 27, 2009

Hunting idle I would suspect TPS or IAC. You replaced the IAC, so how does the TPS test out?

Pharaoh XJ · May 27, 2009

Had one laying around swapped them exact same issue

one more thing when its stuttering & i try to WOT : I heard loud POP in the TB like a backfire but in the TB.

& when symptoms appear, if I drive it wont get past 2000 rpm then suddenly works fine

jneary · May 28, 2009

also check the injector connectors, sometimes the blades bend in on the injectors when reconnecting them

jneary · May 28, 2009

are the plug wires going bad

winterbeater · May 28, 2009

What about starting by fixing your vacuum leak?

Pharaoh XJ · May 28, 2009

I cant seem to spot the vacuum leak, but I tried to unplug the auxiliary vacuum circuit & placed my finger over the manifold opening, didnt fix it, so I am guessing it has to do with the main engine vacuum.

Yesterday I found Oil in my airbox coming from the valve cover breather, can a PCV cause that ?

SeansXJ · May 28, 2009

oil in the airbox is a common thing, get used to that. check the vacuum canister, i had the same issue and i found a crack in the line.

joe_peters · May 28, 2009

Pharaoh XJ said:
I cant seem to spot the vacuum leak, but I tried to unplug the auxiliary vacuum circuit & placed my finger over the manifold opening, didnt fix it, so I am guessing it has to do with the main engine vacuum.

Yesterday I found Oil in my airbox coming from the valve cover breather, can a PCV cause that ?

Usual sign of a plugged CCV (PCV valves not used) system, check the orifice in the valve cover rear, check the vacuum line running from there to the manifold, check the manifold port for vacuum.

Johnnie Walker · May 29, 2009

You checked your map sensor, It is something I overlooked for a bit.

Pharaoh XJ · May 29, 2009

Johnnie Walker said:
You checked your map sensor, It is something I overlooked for a bit.

How can I do that I checked the vacuum line connecting it to the intake. Is there a way to check it electrically ??

Strange is that my milage is the same & my exhaust doesnt seem to have anu carbon build up

Ecomike · May 30, 2009

So far it sounds like it might be a bad oxygen sensor's (Pre-cat) internal heater not heating up right away, and giving bad data to the computer until the engine is hot.

Pharaoh XJ · May 30, 2009

I dont have an oxygen sensor, I have the leaded fuel ECM.
Can this be due to a fuel/injector issue ?

winterbeater · May 30, 2009

If your intake gasket fixed it before, I would realy focus on that again. One test is to take a propane torch (open, but unlit) around the areas of suspect and listen for change in idle.

Doesn't really sound like an injector issue. Possibly fuel pump. You should hook up a fuel pressure gage to the fuel rail.

Pharaoh XJ · May 30, 2009

I did the intake gasket twice, 1st time I reused my gasket + RTV, second time bought a new mopar gasket & tightened the bolts after 500 miles, still same issue.

I am eliminating the vacuum leak theory, tried carb cleaner, tried smoke, didnt notice anything.

Its starting be more frequent now I added 2 bottles of fuel injector cleaner still nothing.

PS: my fuel pump has 155 k miles on it. Can this be a fuel pump issue ?

winterbeater · May 30, 2009

Yes, borrow or rent a fuel pressure sensor. Check the pressure and then check the volume. 49.2 +/- 5.0 PSI and then 1/4 liter minimum flow in 7 seconds. Do not operate open for more than 7 seconds. (Run a hose into a jug.)

Rough Idle really annoying !!! HELP

Pharaoh XJ

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