Erratic Idle.

[betomonroy]

Hi everybody. My truck developed sudenly an erratic Idle speed. I checked the IAC which seemed pretty clean. I cleaned it anyway but the erratic Idle speed continued. I removed the throtle body, inspected it and cleaned it too (even though I clean it once a month and it was not it's turn).
I also inspected the cam sensor and the conection to my Coil. The sensor had very little dirt and all I did to clean it was to wipe it with a clean rag.
Any sugestion?

 

[Wicked_Sludge]

try unplugging the TPS while the engine is running...if it settles down your TPS is bad.

 

[simple guy]

May be a vaccum leak. Check the PCV or lines coming from and going to the manifold and inlet tube. You could always disconnect the battery for a few minutes to rest the ECU.

 

[betomonroy]

I've already done all this...Same result.
Any other guesses???

 

[Wicked_Sludge]

what happends if you unplug the IAC with the truck running? does it smooth out?

 

[moo]

I had the same problem, try unplugging the VSS on the back of the trans.

 

[mtm006]

My 3.slow has always had a "rough" idle. I took it to the dealer when it was still under warranty to have the master cylinder replaced. The service department person seemed concerned about how engine was idling. They kept it for about 2 days and decided that the "rough" idle is normal for the 3.0. I don't know if that helps any, but that's what the dealer told me.

 

[Wicked_Sludge]

i can stand a quarter on edge on top of the intake plenum while my engine is running.

 

[MUDDING B-3000]

my engine does the same thing i changed the IAC an it still does the same thing but my truck smooths out after a little while, an sometime when i just start my truck an drive it an slow down it will stay at 2000 rpms an so ihave to just creep the truck with the clutch an it will bring the idle downto like 1000 rpm

 

[fixizin]

i can stand a quarter on edge on top of the intake plenum while my engine is running.

Yes, but most of us can't afford a Ferrari... seriously, how do you do it? Actually, mine may NOW, finally, be idling that smooth, after new IAC, DPFE, and other maint... will have to try the "QUARTER ON EDGE" TEST.

 

[Wicked_Sludge]

mine had burnt exhaust valves when i got it. replacing them netted me about 30psi of compression in each cylinder and evened the power balance out a lot. aside from that, keeping up on all maintainence items is of the utmost importance.

im even running 25 degrees base timing and i didnt loose any idle quality. the vulcan is just a great running engine.

 

[betomonroy]

Thanks for your info... I did all... IAC, DPFE, Vaccum Lines (there is not too many of them), VSS (wich I don't see the conection but i tried it anyway). I still have and idle that looks like one spark plug doesn't work one time out of ten times some times one out of fifteen tiems. I also tried disconecting each one of the spark plugs one at the time to see which one was the one missing but it is indifferent. I never encountered such thing.
In the mean time one of my catalythic converters powderized its inside and clogged the last one creating an even more bigger puzzle. I'm running out of money and now Christmas is arround the corner. I hope we can fix it before Christmas.
What do You think guys?

 

[Wicked_Sludge]

we're rapidly running out of ideas short of plugging it into an OBDII scanner capable of datastream....

 

[Viva*the*Ranger]

I have had the same problem for about 2 years. At first I tested the fule pressure and it was low so I replaced the filter and pump. It ran better but it still itdles rough. I'm some what of a new-b so I'm not sure what your acronym's are. IAC, DPFE, VSS? I have always done my own work, but I just move to Seattle and all my knowledgable friends are in California. I could use a little help. I would love to resolve this problem!

 

[Wicked_Sludge]

IAC: idle air control (solenoid). controls the engines idle.

DPFE: delta pressure feedback EGR (EGR of coarse is exhaust gas recirculation). the sensor used by the PCM to regulate EGR flow.

VSS: vehicle speed sensor. tells the PCM how fast the truck is moving, used to control various functions of the engine.