OK, i give up!

[DonM]

95 XLT 4.O

Just before X-mas i had a new IAC motor replaced after taking my X in because of the idle being rough! The new IAC didnt seem to help much!? After about three or four months the same symtoms accured again. When stopping at a red light or stop sign the engine seemed as though it wanted to stall, better never does! This happens once out of every 20 or so stops, more so in the mornings after the X had been stitting over night.

Now i did a search for past threads on this but im stuck, i know what the problem could be but im not sure what im looking for. I dont know where the IAC or MAF is?

BTW, it seems to idle better when the A/C is on, when i turn A/C off, it gets worse!

:EDIT: I forgot to mention, i had the shop check it out and there telling me it's normal. My Mech cant find anything wrong. When i did the search for this, other members also had their shop look and couldnt find anything either!


Don

 

[88vert]

IAC is your idle air control valve and it sounds like that is your problem.I am not sure where it is located on your ex.Give Jason 25 a pm he should know where it is

 

[DonM]

OK, ill do that!

Thanks


Don

 

[fastcougar]

Sounds like it's missing pretty bad to me if the IACV was already replaced. The IACV can be tested quite easily. Disconnect the IACV from the Upper Intake Manifold and turn it towards you. Now have some someone inside the truck turn the key to the "On" position ... NOT "Start". The valve should recieve power with the fuel pump and you will hear a click and notice the valve open if it is operational since the IACV must be open for the engine to start since the Throttle Body is closed. If the valve doesn't open, it's most likely defective.

Otherwise, you will have to "Hot Wire" the IACV to test it. This is done by disconnecting the pigtail to the plug and noting which prong inside the housing corrilates to the red wire from the pigtail ... this is the power lead. Then simply find a way to get power to that prong and ground the other ... both the ground and the power can be "jumped" from the battery with some small electrical grips attached to small gauge wires at both ends. Then run the wires to the appropriate battery terminals and then again to the prongs. Be sure the + batter terminal connection goes to the prong that corrilates to the red wire in the pigtail. If it opens, it's operational and you should look elsewhere for the cause.

Like I said, sounds like a mis-fire, which is most likely caused by one of 5 things:

1) Bad Plugs (check plug condition and gap first)
2) Bad Plug Wires
3) Bad Ignition Module
4) Bad Fuel Injectors
5) Bad Fuel Pressure Regulator

Good Luck!

 

[DonM]

Well i just checked the IAC and did the first test you mentioned! I heard a clicking noise when ignition was turned on, but i didnt see any moving parts like the valve open!!

Don

 

[410Fortune]

Rough idle on a 4.0L =


Tune up time!

1. Clean the MAS sensor wires following the instructions on this site

2. Clean the IAc valve, test it if you think the solenoid/plunger is bad (never seen a bad one yet)

3. Replace the fuel filter. People always overlook the fuel filter. I replace mine every 30K miles or so, they are VERY picky about filters, a dirty filter will cause all sorts of rough idle and hesitation problems

4. New spark plugs if they are old

5. At 60K miles the 02 sensors need to be replaced, you can test them ,some last 100K miles, some last 15K, 60K is the suggested interval. A faulty 02 sensor will usually set a code or CEL but not always.

6. You can also clean the entire upper intake manifold including the throttle body, it doesnt do much good to clean the carbon out of the IAC valve if the carbon thats clogging it is inside the intake.

7. Replace the EGR valve and clean lines, if so equipped.

8. If that stuff deesnt work then check fuel pressure at the rail, runthe KOEO and KEOR tests.

Remember any time you replace a sensor or change the signal the PCM is gonna get ( a clean MAS sends a more accurate signal to the comp then a dirty one will) you need to reset the computers memory, drink a beer with the - batt cable disconnected...


This is what I consider a full tune up on a 4.0L and has solved every single runability problem I have ever seen, except for in my case when the PCm itself has gone bad.....

Of course I didnt get it all, dont overlook the plug wires, boots, dirty connections at the coil pack, thermostat, oil change, trans fluid change, diff fluid change, etc....

 

[SteveVB]

MAF

Have the MAF checked, could be a ton of things though, TPS, and the IAC.

Jason25 has a thread going with similar symptoms might want to check it out. Fuel pressure in the general section.

 

[DonM]

Ok guys, will do!


Don