Surging condition

[caddman6425]

94 Explorer XLT 4.0L 4x4

Experienced a condition of missing, after got warm up and driven, when restarted. Seemed to go away after increasing throttle and the release, cleared its' throat. I was working on a frame up restore and didn't have the time to even work on my own car, but all of a sudden it changed to a surging condition. At first I thought it was loading up an knowing this, I thought that I'd work on it latter because I could live with it for awhile. But this???
I'm not really a Ford man and it has me a little lost, I'm thinking vacuum leak somewhere, but where? Oh, the IAC never seemed to work, another thing on my list to do, and now it acts as if the motor is engaging on and off on the IAC, so I unplugged it and the surging stopped. Could the IAC be engaging on and off, and if so what would cause it to do so? Haven't searched the circuits that much and am looking for a starting point. I did check vacuum after disconnecting IAC and have no fluctuation.

 

[trashtruck]

if you're adventurous, the iac can be cleaned. a new one isn't that expensive. might also want to try cleaning the maf sensor. dpfe sensor is also a known trouble point.

 

[caddman6425]

Ya know, right before I unhooked the IAC, I wiggled the connector to the dpfe sensor and it cut out, per say. Hmmm, thanks, I'll look at that.

 

[Centaurious]

If you replace the DPFE Sensor get the Airtek/Wells brand. It is a totally re-engineered part. I got mine at AutoZone.

 

[caddman6425]

Hey all, got a question. What directly controls the IAC, so I guess I'm asking what directly controls the ECU to control the IAC?

 

[Centaurious]

Probably the crank sensor. The ECU uses the crank to determine TDC so it can trigger spark at the correct time. It would make sense to use it for RPM and Tach and thus control the idle with the IAC. The camshaft sensor is used for the Injector timing.

If your Tach is reading correctly and smoothly the ECU should be getting a good signal.

Under the front of the Upper Intake Manifold and behind the Throttle Plate is a vacuum hose. This hose runs back under the manifold to the Charcoal Canister's Purge Valve and should be inspected. Be careful the plastic fittings on the Purge Valve are brittle and break easy if you try to remove the hoses.

The IAC can be removed and cleaned with carb cleaner and the ports in the manifold reamed open as well. This area of the manifold gets dirty from the EGR.

Reading the KOEO, KOER, and Memory codes would be a good idea. Test procedure is in the stickies.