Rough idle

[colocat94]

Hey everyone,
I have a 94 ATX with about 145K miles on it. I performed upper and lower 60K on it when I bought (~2000 miles ago) along with both O2 sensors. New plugs and plug wires too. About 500 miles ago, I noticed a slight stumble or pause occasionally at idle (only at idle). At first I thought it was a tranny issue, since I would kick it into neutral and it would go away. It only happened occasionally, so I didn't pay much attention to it.

Lately, the stumble is getting much worse, but still only at idle when the engine is warm. It isn't related to the tranny. It does it in Drive, Neutral and Park. If just a little pedal is given, it goes away (>1000 RPM). I think that originally when I kicked the tranny into Neutral, just enough RPM was gained by that the problem did show up. Now it doesn't change anything. It also doesn't appear to be the same cylinder missing or a pattern of sort. No CEL, no mileage or power issues, just a rough idle when warm. I have not had any misfires/stalls or anything else related to ignition when driving. Also, there is no water or oil in the plug wells. I love the car and just want to get this thing figured out.

Any pointers before I begin the goose chase?


Bryan

 

[AREA 91]

Double check the correct firing order
How's the ERG valve, and DPFE sensor?

 

[colocat94]

Firing order is fine. The car ran for 1500+ miles with no glitches. Short of a CEL or code, how do I check the DPFE and EGR? This really acts like an ignition issue, but I'm not sure what would cause it only at an idle. Would the cam position sensor or crank sensor cause this kind of problem? How about the DIS module?

Pointers appreciated.

 

[jedhead]

Have you tried to reset the idle?

Idle Reset

NOTE 1: The Ford owner's manual directs that the idle program be relearned following any service when the battery has been disconnected. To do this, it states that the engine should be started and allowed to idle for the (approximately) 70 seconds without touching the gas pedal. Adding the accessory loads ensures that the EEC and IAC valve can accommodate the additional air flow requirements and still maintain the programmed idle speed.

NOTE 2: It is preferable that the car be driven immediately after setting the idle programming. While driving, allow the coolant temperature to rise to the normal range and run the car through its entire performance range.

Idle Speed Program Reset Procedure
-----------------------------------------
1) Disconnect the negative battery terminal.
....Optionally, disconnect the keep alive memory (KAM) connector in the small
....wire also landed to the negative battery terminal.
2) Wait at least 30 seconds.
4) Reconnect the KAM connector or negative battery terminal.
5) Start engine normally (never press the gas pedal).
6) Allow the idle speed to settle for at least 30 seconds.
7) Within 70 seconds of starting the engine, concurrently apply all accessory loads.
....a) Climate control to MAX A/C.
....b) Headlight switch ON, brights ON.
....c) Turn steering wheel slowly ~1/4 turn side to side.
....d) Press brake pedal.
....e) ATX SHOs only: shifter to DRIVE.
8) Do not turn off engine for at least 5 minutes.