Rought Idle at cold start, then it goes away... What gives?

[B94Sport]

Rough Idle at cold start, then it goes away... What gives?

Two or three days ago I noticed that when I would start my Ex for the first time during the day, it would idle very rough. The idle RPM was normal, but the exhaust sounded strange and smelled funny (almost sweet?), and the truck shook a little. Anyway, after I drive the truck for a minute or two (actually drive it, not just set it in Drive and rev the engine), the rough idle and exhaust problems go away. If I shut the truck off and go back and start it up again within about 15 minutes, there are no rough idle problems. I have not gotten a CEL. This has not been going on long enough for me to be sure whether or not fuel economy is suffering. Anyone have any suggestions?

 

[B94Sport]

I just got back from a long drive... No effect on gas mileage. Anybody?

 

[Todd W]

clean the MAF sensor

 

[Quakecom]

same thing happened to me...

I have had the same thing happening to me (rather my X). Same exact problem. Turns out that the intake gaskets (I think that was it) had holes in them. The reason why it goes away after a couple of minutes is that then the engine has warmed up enough for the holes to close and everything is fine. But when the engine is first started up, the engine is cold and the holes are big enough to cause the rough idling.

Hope this helps...Fixed my problem

Quakecom

 

[B94Sport]

Really... Well I know it is not the MAF, I cleaned that 1900 miles ago when I changed my oil and trans fluid (trans fluid and MAF get serviced at the same time - every 10K). To add to it, today I started the truck and there were no problems whatsoever. Very odd. I have not yet attempted to pull codes, but I am willing to bet I won't get any codes from it.

 

[Opera House]

Stress cracked plugs

I bought a 97 last year with a little over 100K. It had a rough idle first couple of minutes after starting overnight. When I bought the car, I pulled the easiest plug to get at and it was fairly new, maybe 15K old. Having many other things that needed work on the vehicle, I didn't check any more plugs. Another 10K down the road, it became rough even when warm. This time I pulled out all the plugs. Seems someone had replaced only the first plug that I inspected. All the rest were origional. Two of those plugs had stress cracks in the insulators just below the boot. Moisture would collect in the cracks and short out the plugs when cold. Eventually, more dirt filled the cracks and shorted the plugs even when hot. I mention this because I had never seen stress cracks in plugs before and wonder if some of these engines are prone to this failure. It also points out that this could be a problem from dirty ignition components like plug wires that are sensitive to moisture.

 

[TJA97Explorer]

I also have 97 X with the same problem. I had the recall done to replace the tensioner. The recall they installed new intake manifold gaskets....Problem was gone !

Good luck

 

[jack1.1]

I just had a similar problem. My Ex is a 5.0. It would idle real rough at 200 -500 rpm and sometimes die when cold. Once it was started and down my street everything was fine. It was strange. Went on for a week, then got the engine check light. I took it to Ford for a $219 raping. Here's what I got:

F672-9F7155 BB Valve Asy-throttle air by-pass
Ford charges $70.52 for it.

I also had to pay $94.00 for the computer check.

Also it is 0.5 labor which cost me $47.00

Don't forget the $3+ in shop rags!

So apparently this part is 10 minute bolt in and I suppose you could get that part for $50. I hope this helps.

Finally any you folks got a good story on what brand of spark plug wires to buy? Jacobs? What works good on a stock 5.0, I'm looking for what works mpg wise.

thanks and good luck,

Jack

 

[JDraper]

Could be the Idle Air Control Valve ( think that's what Jack1.1 is referring to as a bypass vavle). It controls how much air bypasses the throttle valve at idle. You can check it electronically with a multi-meter. With the key on, engine off, you should get between 10.5 and 12.5 volts on the wiring harness leading to the IAC. Across the IAC terminals shoud be between 6.0 and 13.0 Ohms Resistance, and greater than 10k ohms from either terminal to the case. If the readings are still good, remove the valve and check for carbon buildup. This will cause the idle to be rough.