'91 Explorer will not idle during inital startup.

[jollykreiger]

Its about as clear cut as I think I can make it.

When I first start it in the morning for about the first 30seconds to 1 minute, the rig will slowly drop the idle lower and lower until it stalls out. If I hit the gas it runs great and will stay running no problem.

If the truck is already warmed up, it will do the same thing for about 5 seconds. After that it gives me no problems.

If the truck is warmed up and I turn the key on but dont start it and wait 5-10 seconds, then it will start and idle like it should.

What gives, I know the IACV is doing something, is it just sticking or is there a temp sensor that isnt working right and takes a while to figure out the current temp?


And in case anybody wonders after that inital startup I dont have any problems. Ive ran it at about 5000 feet elevation in 1.5' of snow while camping, and back down to 1000 feet back in 100 deg weather and never had a problem except on the first startups. (after sitting more than ~10 minutes to be clear)

 

[BLOODBANE]

Any check engine light? the IAC in my 94 has given me fits in the past, but the replacement I bought makes it run worse (I keep it because it was installed and just never took it back). I had to replace the computer once, but I had all kinds of different CEL codes at different times (one time it would be MAF sensor, next scan would say IAC, next scan would give lean bank, etc...)The TPS could also be giving you fits (easy to change out).

I would get a code reader on it before I started throwing parts at it though. We could guess all day and never get you lined out straight.

 

[RonD]

I would change the ECT sensor, under $10, just on spec.
Fuel injected engines have TWO temp units.
ECT sensor, 2 wires used only by the computer
ECT SENDER, 1 wire used only by the dash board temp gauge

The 2 wire ECT sensor is what tells computer to run "choke mode" or regular warm engine mode.

A cold engine needs richer fuel mix and higher idle, the point of the choke plate on a carb, fuel injection has no Jets to suck extra fuel out of and no idle screw so the computer has to set choke electronically, open injectors longer and open IAC Valve more.

And you will want to clean the IAC valve, free to do and not that hard.
Also clean the MAF sensor(assuming 4.0l).
These should both be cleaned every 5 years or so

 

[jollykreiger]

Ok, I have no idea if the cel is on as it never turns on so I assume the bulb is not working or broken or ... I dunno.

I change out the 2 wire ect sensor and no change, I cleaned the IAC valve before hand when I first got it but no change, so I'm thinking the maf, I was gonna clean it but apparently my cleaner is missing so I gotta buy some more.

 

[Zero_Cool]

could be that the IAC could have failed entirely

 

[theAntihero]

I had the same problem with my 00 explorer 4.0 OHV. I replaced it but before i got the part i whacked it softly with a hammer and it worked for awhile lol

 

[Locotomb]

Sounds like you might have a bad ECM. I had this issue and waited until all my other ideas failed and sure enough, My computer had a bad circuit. The one that controls the Cold Crank scenario. Mine as well would start up fine after the initial start. Probably because It will start in the Warm Crank scenario there on after. I luckly have three of all the sensors on hand so I had plenty of known good sensors to test with. If you can, get your hands on a known ECM and see if it fires up right.

Opps, old thread.

 

[stsalvage]

Remember there are 6 major things that happen on the OBD1 rangers Be glad you or we don't have the EGR valve what a pile that thing is. The Mass airflow needs to be cleaned ever so often check the air filter the IAC the O2 sensor the Idel control peace on your throttle body the 2 temp senders the Injectors might need to be replaced and the one that most people forget Battery cables If your truck is not getting 12 volts to the computer Or a good ground your truck will run like sh-t I own 4 fords with the 4.0 all but 1 is a 5 speed . Love these trucks there so easy to work on

 

[jtaborsky]

I suspect the fuel pump. Do you hear it prime when you turn the ignition on? What's your fuel pressure when you turn the ignition on? Does fuel pressure hold or drop? I THINK that year Ex has a check valve in its fuel pump.

 

[stsalvage]

I was talking to a guy that told me If your having all sorts of problem time to check the power control module the thing on the core support next to the battery

 

[RonD]

The above is the Spark control module, an EDIS-6 use for 4.0l OHV

They rarely have issues, but can be damaged if there is a front end collision, as said they are located on the rad support, often on the front side for better cooling
And after a repair of the front end they may not have been replaced