Help with cold rough idle

1834kc · 03-26-2011, 07:57 PM

I have a 91 Explorer and finally have the cooling system in order. New water pump, and radiator and thermostat. Flushed the system very well, and now its clean as a whistle and runs at the right temp.
However, 3 or 4 weeks after all this is done, it has started missing badly when its cold. After it reaches operating temp. it smooths out. I figure it may be a head gasket, but I really need some expert advice before I get into that. It did over heat one time, but according to the gauge, it didnt go critical. Probably a faulty gauge, right?
Is there anything I need to check before I jump in with the head gasket? Sensors, relays? should I have it put on a diagnostic machine? As is the norm, money is tight, so anything that I can do at home without making it worse would be helpful.
I did try plug wires, (no difference) and have the plugs to put in yet.
Thanks for your time,

CumminsCowboyNE · 03-28-2011, 12:02 PM

Try the idle air control valve. This regulates how much air the motor gets at an idle. Also I'm not sure if you truck has it but the mass air flow sensor will really play heck with how the motor runs. I'm sure somewhere on here is procedure for cleaning and or replacing these.

*Roadrunner777* · 03-28-2011, 01:33 PM

The IAC is readily available on the upper manifold, look for pictures in other threads. When you experience the rough idle, tap on it a little bit, see if it gets better.

Check engine light on? If so, yeah, go to autozone or someplace and have them read out the codes, post them here.

1834kc · 03-28-2011, 05:18 PM

Thanks for your help. I have cleaned the Mass Air Flow Sensor, (found directions here). I have also cleaned the IAC, (also learned here). When I tap on the IAC nothing changes.
Is the wire connector on the end supposed to move? It turns 1/8 inch or so, and feels loose. I dont know how this functions. Is it possible to have a vacuum leak from this end? I have checked all the vacuum lines including the one at the trans. by removing the panel in the floor between the seats. (yet again learned here).
You people rock!

CumminsCowboyNE · 03-28-2011, 05:27 PM

If you think you have a vacuum leak take a can of carb cleaner and spray all the areas that you suspect to be leaking and spray them with the cleaner. if any makes it to the intake your motor will either speed up or if enough gets in may make the motor sputter. spray all around the intake and any vacuum hoses you can find maybe you will find something. Good luck.

P.S. I know you probably know but your motor needs to be running while doing this. Just trying to cover the bases.

1834kc · 03-28-2011, 08:24 PM

Thanks for the tip, and your time. I'll try it tomorrow, along with the Autozone suggestion and post the codes I get.

1834kc · 03-31-2011, 06:04 PM

Sorry, but havent gotten any codes yet. I was looking on line for parts just to see what I was up against depending on codes, and found an IAC new for 24.00 plus shipping. I figured it couldnt hurt to have it.
I have read in many posts here, that there could be an issue with intake gaskets? I dont know the repair history of my truck, but it has 188,000 miles on it. Is this something that I should do as preventive maintenance?
Also, when I put my finger on the fuel line going to the rail, I can feel a thump every second or so. Is this normal?
As soon as I get the codes, maybe some of this will become clearer.
Thanks again for your time and suggestions.

*Roadrunner777* · 03-31-2011, 06:31 PM

Lower intake gasket... I guess it depends on how pro-active you want to get with the vehicle. I'll be doing mine in a month or so, just to know it is done and correct, and I won't have to address it in winter months. Be a good time for plugs and wires too. And rocker panels. And new bumpers.

1834kc · 03-31-2011, 08:07 PM

Proactive or self preservation. Not sure which at this point. Window motors, A/C, drivers power seat, door handles the to do list grows larger, but thanks to several people here, I have saved tons of money on labor and parts by doing the work myself.

1834kc · 08-15-2011, 06:31 AM

Finally got off my butt and checked the plugs. Low and behold one was broken. The porcelain under the electrode was broken and jammed up into it. The plug was fouled. The other 5 were burnt a light brown color. Now it runs like a top. Thanks for all your help.

03-26-2011, 07:57 PM	#1
1834kc Wannabe Elite Explorer Jasper Georgia 1991 XLT 4x4 Join Date: May 2010 Posts: 21 Vehicle Specs (Original Poster)	Help with cold rough idle I have a 91 Explorer and finally have the cooling system in order. New water pump, and radiator and thermostat. Flushed the system very well, and now its clean as a whistle and runs at the right temp. However, 3 or 4 weeks after all this is done, it has started missing badly when its cold. After it reaches operating temp. it smooths out. I figure it may be a head gasket, but I really need some expert advice before I get into that. It did over heat one time, but according to the gauge, it didnt go critical. Probably a faulty gauge, right? Is there anything I need to check before I jump in with the head gasket? Sensors, relays? should I have it put on a diagnostic machine? As is the norm, money is tight, so anything that I can do at home without making it worse would be helpful. I did try plug wires, (no difference) and have the plugs to put in yet. Thanks for your time,

03-28-2011, 12:02 PM	#2
CumminsCowboyNE Wannabe Elite Explorer Silt, Colorado '94 Explorer Join Date: Mar 2011 Posts: 4 Vehicle Specs	Try the idle air control valve. This regulates how much air the motor gets at an idle. Also I'm not sure if you truck has it but the mass air flow sensor will really play heck with how the motor runs. I'm sure somewhere on here is procedure for cleaning and or replacing these. __________________ 2002 Dodge 3/4 ton, cummins, 6spd. Little air little fuel lots of fun. 1994 Ford Explorer Can't seem to keep it going for a month.

03-28-2011, 01:33 PM	#3
Roadrunner777 Bemidji, MN 94 4x4 Sport 88k Join Date: Feb 2011 Posts: 1,279 Vehicle Specs	The IAC is readily available on the upper manifold, look for pictures in other threads. When you experience the rough idle, tap on it a little bit, see if it gets better. Check engine light on? If so, yeah, go to autozone or someplace and have them read out the codes, post them here. __________________ 1st Gen Fuel Pressure Not ready for prime time link list KD0SCJ

03-28-2011, 05:27 PM	#5
CumminsCowboyNE Wannabe Elite Explorer Silt, Colorado '94 Explorer Join Date: Mar 2011 Posts: 4 Vehicle Specs	If you think you have a vacuum leak take a can of carb cleaner and spray all the areas that you suspect to be leaking and spray them with the cleaner. if any makes it to the intake your motor will either speed up or if enough gets in may make the motor sputter. spray all around the intake and any vacuum hoses you can find maybe you will find something. Good luck. P.S. I know you probably know but your motor needs to be running while doing this. Just trying to cover the bases. __________________ 2002 Dodge 3/4 ton, cummins, 6spd. Little air little fuel lots of fun. 1994 Ford Explorer Can't seem to keep it going for a month.

03-31-2011, 06:31 PM	#8
Roadrunner777 Bemidji, MN 94 4x4 Sport 88k Join Date: Feb 2011 Posts: 1,279 Vehicle Specs	Lower intake gasket... I guess it depends on how pro-active you want to get with the vehicle. I'll be doing mine in a month or so, just to know it is done and correct, and I won't have to address it in winter months. Be a good time for plugs and wires too. And rocker panels. And new bumpers. __________________ 1st Gen Fuel Pressure Not ready for prime time link list KD0SCJ

03-28-2011, 05:18 PM	#4
1834kc Wannabe Elite Explorer Jasper Georgia 1991 XLT 4x4 Join Date: May 2010 Posts: 21 Vehicle Specs (Original Poster)	Thanks for your help. I have cleaned the Mass Air Flow Sensor, (found directions here). I have also cleaned the IAC, (also learned here). When I tap on the IAC nothing changes. Is the wire connector on the end supposed to move? It turns 1/8 inch or so, and feels loose. I dont know how this functions. Is it possible to have a vacuum leak from this end? I have checked all the vacuum lines including the one at the trans. by removing the panel in the floor between the seats. (yet again learned here). You people rock!

03-28-2011, 08:24 PM	#6
1834kc Wannabe Elite Explorer Jasper Georgia 1991 XLT 4x4 Join Date: May 2010 Posts: 21 Vehicle Specs (Original Poster)	Thanks for the tip, and your time. I'll try it tomorrow, along with the Autozone suggestion and post the codes I get.

03-31-2011, 06:04 PM	#7
1834kc Wannabe Elite Explorer Jasper Georgia 1991 XLT 4x4 Join Date: May 2010 Posts: 21 Vehicle Specs (Original Poster)	Sorry, but havent gotten any codes yet. I was looking on line for parts just to see what I was up against depending on codes, and found an IAC new for 24.00 plus shipping. I figured it couldnt hurt to have it. I have read in many posts here, that there could be an issue with intake gaskets? I dont know the repair history of my truck, but it has 188,000 miles on it. Is this something that I should do as preventive maintenance? Also, when I put my finger on the fuel line going to the rail, I can feel a thump every second or so. Is this normal? As soon as I get the codes, maybe some of this will become clearer. Thanks again for your time and suggestions.

03-31-2011, 08:07 PM	#9
1834kc Wannabe Elite Explorer Jasper Georgia 1991 XLT 4x4 Join Date: May 2010 Posts: 21 Vehicle Specs (Original Poster)	Proactive or self preservation. Not sure which at this point. Window motors, A/C, drivers power seat, door handles the to do list grows larger, but thanks to several people here, I have saved tons of money on labor and parts by doing the work myself.

08-15-2011, 06:31 AM	#10
1834kc Wannabe Elite Explorer Jasper Georgia 1991 XLT 4x4 Join Date: May 2010 Posts: 21 Vehicle Specs (Original Poster)	Finally got off my butt and checked the plugs. Low and behold one was broken. The porcelain under the electrode was broken and jammed up into it. The plug was fouled. The other 5 were burnt a light brown color. Now it runs like a top. Thanks for all your help.