Rough Idle and Engine Surge Under Load

[mikepier]

Mike,

Just a word of caution: I wouldn't blindly replace things without being absolutely sure. Based on your description, I would first check the "air" side of things (air filter, MAF, IAC, vacuum leaks, etc.). These things are easy to get to and relatively cheap to clean/replace. In my experience, bad sparkplugs will cause driveability issues along with a rough idle, too (low/no power, skipping, etc.). I haven't heard of spark plugs only causing rough idles and nothing else (I could be wrong here, at least it hasn't happened to me).

A word on CELs: Even though the CEL is not lit, your PCM may have codes "pending" (that is, your computer isn't sure if the issue is a constant problem). If a code is "pending" for some time, your CEL will come on. I would stop by your local auto store and borrow their handheld scanner to see if anything is pending.

Good Luck!

ERUSH

The air side as far as I can tell looks good. New air filter, I cleaned the MAF and IAC, and I don't see or hear any leaks. But I know what its like to replace things and it does not fix it. I do not want to fall in that trap.
So I'll keep it in mind.

 

[48prerunner]

This whole thread sounds like what i had a problem with with my wife's 98 4.0 sohc. it was the intake manifold gaskets not a really hard job to replace they are like o rings its adry manifold so no need to drain coolant. just lots of stuff to take off to get to it.

 

[mikepier]

This whole thread sounds like what i had a problem with with my wife's 98 4.0 sohc. it was the intake manifold gaskets not a really hard job to replace they are like o rings its adry manifold so no need to drain coolant. just lots of stuff to take off to get to it.

I don't think its the intake gaskets because the issue with them is it occurs when the engine is cold. My issue occurs when its warmed up.

I did another test, I removed each plug wire at the coil while the engine was running and did not notice anything strange. Each cylinder that was disconnected made the engine behave the same way. So that tells me the plugs and wires are good. It might be the coil, its 10 years old, but it runs great otherwise.

 

[ERUSH97XLT]

Mike,

Do you know how to inspect your coil for proper operation? I would check it to make sure its electrically sound before replacing it.

ERUSH

 

[mikepier]

Mike,

Do you know how to inspect your coil for proper operation? I would check it to make sure its electrically sound before replacing it.

ERUSH

I followed the Chilton Manual and put a meter on the coil between each shared terminal. It says normal is between 6,500-11,500 ohms. I got a consistent reading of 12,500 ohms between all 3 terminals, so I'm assuming this is normal. The truck runs flawlessly while on the highway or in town, its just at idle I have an issue, so I don't know if a bad coil will act up just at idle or not.

 

[team]

I followed the Chilton Manual and put a meter on the coil between each shared terminal. It says normal is between 6,500-11,500 ohms. I got a consistent reading of 12,500 ohms between all 3 terminals, so I'm assuming this is normal. The truck runs flawlessly while on the highway or in town, its just at idle I have an issue, so I don't know if a bad coil will act up just at idle or not.

I got the same resistance on my coil pack also (12,500 ohms), so I went to advance auto parts with my mulitmeter to measure their new one before I purchased it. Their's was ~13,500 ohms! So I convinced them to let me return it if it didn't fix the idle problem and it ran the same as the old coil pack so I returned it back to them.

 

[mikepier]

I got the same resistance on my coil pack also (12,500 ohms), so I went to advance auto parts with my mulitmeter to measure their new one before I purchased it. Their's was ~13,500 ohms! So I convinced them to let me return it if it didn't fix the idle problem and it ran the same as the old coil pack so I returned it back to them.

That great that they allowed you to return it. Saved you about $100. Most places do not take returns on stuff like that.
Apparantly this "vibrating" idle issue I'm having was a big issue on 97's and 98's. There was a TSB put out that noted the vibration and the fix was for a new power steering hose and a y brace for the muffler. But it was to have been resolved after 99 models were put out. I guess its a coincidence.
I removed each plug from the pass side today to inspect for anything unusual, and everything looked good.

 

[tigger59]

i have a 99 explorer 4.0 engine. over the last 4 month i have had an issue when from a stop as i step on the gas not all the time though, it will sputter. in the last couple of weeks after driving for a while at a stop light waiting the idle will get real ruff. I had a tune up 10,000 miles ago, tried gas treatment, chevron plus and super. and my check engine light has not come on either. any ideas!