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Old 10-05-2011, 05:18 PM
RobMD RobMD is offline
Fix Or Run Down
Join Date: Oct 2011
Posts: 19
Default '99 Rough idle/Misfire 2.5L

Hey guys,

This would be my first post but I'm no stranger to a Ford Ranger. I've owned mine for 7 years now since it had 38,000 miles on it. It's a 5 speed 2.5L multi-port extended cab 2WD. It now has 139,000 miles on it and is a daily driver.

My problem has existed for years. I've pondered, thought and thought some more about my problem. Yes, being a mechanic at Deere, I'm quite capable of maintaining my truck, 3,000 mile oil changes, timing belt changes, new water pump... I could go on and on about all the maintenance i've done to it.

A quick search in the forum archives about my specific problem showed a lot of compression tests, fuel filters, IAC tests and EGR replacements that solved nothing for the owner. I suspect it's one of those crazy computerized dilemmas which have no end.

So.... maybe someone can put some new ideas into my brain.


Engine starts and runs normally when cold. After 5 minutes of driving and approaching a stop sign, engine begins loping and shaking the whole truck. People in my rearview mirror have actually pointed and mouthed "it's a shaking truck." This shaking affects how I leave off in 1st gear, and often causes concern when trying to pull out onto a busy street.

Note that the engine will smooth itself out and idle normally as if my problem doesn't exist. Slap the gas pedal and voila, the mysterious shaking returns. At 1/4 to wide open highway speed throttle ranges, the engine runs smooth.

The problem is magnified when the engine is cold. When it's warm, the problem is less and less apparent. When the weather outside is cold, the engine takes longer to stop misfiring and running rough but eventually goes away.


Only one code has been coming up the last 30,000 miles: Cylinder 2 misfire.


IAC and throttle body cleaned half a dozen times over 100,000 miles.
EGR vacuum lines checked and EGR cleaned/checked.
Spark plugs and plug wires changed twice.
MAF sensor unplugged/cleaned - MINOR difference.
Fuel filter change 20,000 miles ago.
Timing belt at 120,000 miles and has made no difference in running - static timing is fine.
Antifreeze changed and waterpump replaced.
Battery and alternator were replaced once (unrelated)
Sprayed WD40 around all vacuum areas - no leaks.
No leaking exhaust, cat not plugged.
Air filter is standard motorcraft paper. I got rid of the K&N because I believe it could have damaged the MAF sensor with all that filter recharger crap.


K&N air filter might have damaged MAF sensor? There is no code relating to the MAF sensor.
Problem is INTERMITTENT and would NOT be a mechanical problem. If the truck did the same thing 100,000 miles ago, and is no different today, why would it be mechanical?
Problem has a little to do with engine TEMPERATURE.


...I HOPE!

Thanks in advance for your input.
Qualified John Deere Mechanic
B.A. in History, York College of PA
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