Erratic IAC action 94 Explorer

[honestjerry]

OK, here goes. 94 Explorer, 4.0 obviously, all stock. The IAC is getting erratic signals from the PCM causing sputtering high/ low idle or sometimes no action and a very low idle. Checked wiring, connectors, several IAC's, went as far as to run a new wire to the computer from the IAC, no luck. Thought the large connectors next to the alternator might be dirty, disconnected, cleaned, ran fine for four days, back to square one.

I have checked, changed and rechecked many things including the plugs mentioned above, now I can't get it to stop acting up at all which tells me I haven't found the problem and now it is probably worse.

Since the wires to the IAC seem to be ok, my next logical thought is, what tells the PCM to send a signal in the first place? Crank sensor? TPS? Combination of things?

This is my daughter's car and has been going on for 3 weeks now on and off. Kinda need some advice here.

Should also mention, no CEL, no codes.

Thanks!
Jerry

 

[Anime]

I recently had a sputtering/stalling/erratic idle issue that was solved by simply replacing the PCM/EEC relay in the engine compartment fuse box. Sometimes the fuel pump relay gets "sticky" from age/heat as well and replacing this also helps. You can swap the relay with one of the non-essential ones in the fuse box to check for a change in operation, just be sure it is the same type/part number since there is one relay in there that is different.

Sometimes the IAC sensor gets dirty and can benefit from cleaning, being removed and some air intake cleaner sprayed on the sensor inside, but it also seems possible to ruin it if you clean it wrong or mess up the parts inside, which of course requires a new sensor to restore normal operation.

The TPS can go as well, mine has been hosed for some time but it just throws a code occasionally and works fine the rest of the time. It's possible for the TPS to send a screwy signal and have the engine systems working against each other, but I haven't heard of any such case on an Explorer so it's doubtful.

Keep the fuel system in mind, if there's a clog in the fuel filter or the pump is getting weak it could be getting erratic fuel delivery at low RPM. If it runs fine at speed though and has no acceleration issues then it's probably not fuel, though.

The Crank Position Sensor is also a likely culprit once you go through and rule out everything else. Definitely worth replacing in the end rather than giving up and taking it to a shop.

The ignition coil pack would also be on my short list of possible candidates for replacement fixes, if it goes bad you can get ignition issues, but it wouldn't just be at idle.


You may want to check some more basic/simple things such as the MAS, spark plugs/wires, and even just all of the wires, connectors, vacuum hoses and caps, etc. as well, sometimes just a worn wire that's rubbing on another or against a metal part can give erratic issues.


The EEC system gets its information from the TPS, IAC, temp sensor, MAS, etc. to control the engine, but not always all at the same time. At idle is when the IAC comes into play, so if the only issue is at idle, it's likely the problem. When the original IAC valve went on mine it caused high idle, only once in a great while would it have low idle and stall, and only on cold start.

 

[honestjerry]

well, I've replaced the IAC with a known good one. Same issue. I'm starting to think the pcm is fragged. I noticed that when it's acting up, it even causes rpm changes going down the road at throttle. I thought the iac was only active at idle? Also, swapped/ changed the fuel and computer relays, no change. It has lately been lighting the "check oil" light, but the oil is full. It goes out on its own after several restarts. One koeo test threw a code related to the fuel pump power circuit. It never repeated and again never had a light. frustrating? you betcha.....