Need suggestions....

[shawn stonbraker 2]

Ok, here is the problem. My ST has been idleing rough for the past 3 weeks. Almost like a "hitch" in the idle. It actually sounds like it's trying to stall when in gear, but but the IAC kicks in and keeps it running (thwump sound). It's more noticable when in gear but you can still hear it during idle. I have done the following:



the plugs were replaced just this past spring, I looked under the hood last night in the dark and didn't see any "fireworks" going off

cleaned and checked the IAC

cleaned the MAF

cleaned the TB

took off the aftermarket intake and put the OEM back on with a new filter

put stuff in the gas to get rid of water

checked for "cracked elbow"



Could it be plugs, wires, or what am I missing? It's getting annoying. There are no codes and seems to run fine when cruising along. No hitch to it's step, just when I come to a complete stop, it starts to stumble around. I'm open to suggestions on what to look for.

 

[Todd Z]

Try to rule out things....



Whats the miles ?



Fuel filter ???



Last plug change ???



I found modded 4.0's need plug changes earlier..... I had a miss at about 36K George at about 60K....



IF you rule out all mechanical issues, See Next :



Do you have an Xcal ???



If so, the Stock RPM idle is set around 600 or 650. I found that i had to raise it to around 700 on my 04 and 800 on my 03 to cure all those stupid annoying things...



Todd Z

 

[shawn stonbraker 2]

Miles= 86,000



Fuel filter= changed at 50K



Plugs= just last Spring and it was about 79K. I'll admit, I have no idea what plugs are in there. I had a local change them this last time. No way in hell was I doing that again.



Wires= never



No XCal, and the RPM is usually just over the half way between the 5 and 10 mark.(I would guess about 750) I do notice that when it really gets bad, it hovers just above the 5 (around 600). I have adjusted the RPM's before to raise them before.



It's always, for as long as I can remember, had a small hitch in the idle when in park. Not this bad though and never when in gear. When in gear it would run smooth. Now there are times the whole vehicle is shacking while it's trying to keep from stalling.



I'm pretty good with mechanical stuff and diagnostics. I truely thought it was the aftermarket intake (just cleaned and oiled the filter about 5 months ago), so that's why I just took it off. I'm tired of cleaning the thing.

 

[Dreman]

You've checked the obvious, but now you have to look elsewhere. It sounds like a vacuum leak. Check the intake manifold, hoses, and anything else connected to the vacuum side of the engine, such as the power brake booster.

 

[Rodger Tellefson]

I suggest that you also change the plug wires and do a Seafoam cleaning too.

 

[shawn stonbraker 2]

R&G, I do the Seafoam every 10K miles.



dreman, that is what I was thinking also (why I checked for the cracked elbow). May try other hoses tomorrow. I was on limited time today, so I did the obvious things.