Unsteady idle

[FXplorer]

The past month or so I've developed a rough idle. When I first start my car up, I have to let it warm up for a few minutes regardless of outside temperature. Her idle waivers slightly at the tach and I can definitely feel it. On several occasions she would start to really idle badly on the verge of dying as I give her gas (that's why I warm her up first). When driving, I sense no loss of power but can sometimes feel a very slight surge. I have seafoamed, changed the TPS, IAC new from Ford about 8 months old. Could this be related to plugs/wires or perhaps bad fuel (fuel filter changed not long ago). Seemed to feel this after Hurricane Wilma passed through. Due to lack of fuel at the time, I filled up my tank with gas from a 4-stroke boat motor. Although that fuel is long burned up, do you think it might've contaminated filter?

 

[Runnin'OnEmpty]

FXplorer, if it was gas from a 2-stroke (oil+gas), that could certainly be the problem. The oil could have coated the injectors or something.....? One thing to try is cleaning the throttle body. Wipe it down where the throttle plate meets the housing; carbon tends to build up there, and cause a poor idle.

ROE

 

[BrooklynBay]

I would have to agree with Roe in his previous post. It's possibe that oil in the system could interfere with the way it runs. A dirty MAF sensor could definitely cause a rough idle. You said that there wasn't any loss in power. A loss in power is usually from the MAF, but then it depends upon how dirty it is. The older Ford systems used a Map sensor, which could also cause a rough idle. An O2 sensor could cause surging, and a rough idle, especially when it is cold. An electrical system with a fluctuating output could cause a lot of problems, since all of the electronics requires a rock steady voltage of about 14.7 volts in order to operate the solenoid controls, like the IAC. This part in Ford terminology is known as the air bypass valve. Last but not least, always check for a leaking vacuum hose. This loss in vacuum could cause a rough idle, stalling, etc.

 

[FXplorer]

I know for sure the fuel from boat is 4-stroke regular gasoline. I tested for vacuum leaks using ether but no gauge. Do you think it could in fact be slight misfiring from the plugs/wires?

 

[ExplorerDMB]

rough idle could easily be caused by a ignition problem (wires/plugs) but if the fuel was contaminated with water you could be sucking more water into your engine than you should.

-Drew

 

[FXplorer]

How long, do you figure, would water or moisture remain in the fuel system? I have fuled up several times since but I still get the unsteady idle. Not dying on me now.

 

[karl_burns]

I've got a pretty rough idle with the same symptoms.
I cleaned the TB/MAF only a few months ago, and about 6 months ago I changed the plugs and wires.
I don't think it's a bad plug, b/c actually one of mine died and I immediately got a CEL. I have been wondering if it's an O2 sensor.... No CELs, but I've got the same weird idle, and sometimes when I brake the idle drops to like 400rpms! It's dies twice too (while braking).
I have an after-market TB, and I noticed the butterfly flap has two tiny holes in it. The stock didn't. I wonder if that's the cause...... Like when I let off the gas, the rpms don;t immediately drop cuz the butterfly flap is taking longer to close....
Karl