Rough Idle

[HNS]

1996 Ford Ranger, 2.3L 4cyl.

It has an intermittent problem. it will idle very rough, thenif I take the thorttle to the floor it will surge-idle-surge-idle-surge-idle-run normally. It will then run fine for a while, then, usually at a stop light, run rough and go through the surge-idle process with the pedal to the floor, then run normal for a while again. It seems to happen mostly right at start. The CHK ENG light is not on. It was on, but the plug on the EGR DPFE was loose from replacing the EGR valve and it went out.

I have replaced:

Spark pPlugs and Spark Plug Wires
Mass Air Flow Sensor
Throttle Position Sensor
Oil/Oil Filter
EGR Valve
2x O2 Sensors
Purge Valve Canister Solenoid and Switch Assembly
Air Filter
Fuel Filter
Idle Air Control Valve

Checked the PCV valve, it's OK

I was thinking:

Timing
Vacuum (not sure how I am going to do that. I looked at the vacuum lines and they all seem good. I pulled the vacuum line off the EGR Valve and put my finger over the end and it had vacuum.)
EGR Vacuum Regulator Solenoid
Engine Coolent Temperature Sensor
Air Intake Temperature Sensor
PCM Computer

Help

Derek

 

[dogfriend]

Did you reset the PCM after replacing above parts? If not, disconnect the battery for a few minutes (or reset with a scan tool). It may have learned something weird that you want it to forget.

If that doesn't help, I think that a vacuum leak is likely. One trick is to use a propane torch (don't light it!). Turn it on and pass it near the areas where you suspect a vac leak while idling the engine. If you have a leak, the propane will raise and smooth out the idle slightly. They also make vac leak detectors which "listen" for the sound. A shop might have one of these, they are kind of expensive for a home mechanic.

 

[dmm5157]

No follow-up to this?

Pitty. I have the same problem. Guess I'll just keep trudging through the forum for more info.