I have a '98 Explorer 5.0 V8 with 144,000 miles. Normally, it runs perfect. But since winter has set in, it idles very rough when its cold, and seems to sound better (but not perfect) when it warms up. My actual idle is steady around 800rpm, but the engine sounds very rough running, like a rumbling sound. I've never any major issues, besides a bad IAC valve, which I replaced two years ago and again just two weeks ago thinking that was the problem. I change my spark plugs every 50,000 along with my wires at 100,000. The CIL is not on and there are no codes showing up when it's scanned. I've seen many posts regarding the intake gaskets on the SOHC and was wondering if the V8 had similar issues. Any other suggestions would be greatly appreciated! Thanks!

-Vivian

 

How about your distributer cap and rotary button? Have you checked those? Also, consider cleaning the MAF and the intake. The 302 doesn't typically have intake leaks.

 

Jerry, this engine (and the V6 as well) doesn't have a distributor. The ignition system is electronic. What you see the spark plug wires connecting to (other than the plugs, that is!) are the ignition coils.

Vivian, it sounds from your description that the truck has a vacuum leak. Open the hood and start the engine when it's cold. Do you hear a whistling or whooshing sound? If you do, track it down and see if you find a vac hose that is cracked or otherwise broken.

Failing that, I'd get a spray can of starter fluid from a parts store and spritz the intake gasket areas and other places where a leak is possible. If the idle gets better, you've found the problem.

Another possibility I just thought of is the EGR valve. If it's not closing completely due to carbon buildup, that could cause the symptoms you describe.

Good luck!

 

Thanks JerrySimm. kevin74656 is right about there not being a distributor cap on the newer Explorers. I think the much newer models have the ignition coils on the spark plugs, making spark plug wires a thing of the past. I have cleaned my MAF, just after replacing the IAC. I just replaced my spark plugs and wires after seeing that one of my wires was crunchy due to it being too close to the cast iron manifold. But that did not fix the problem. The EGR valve was next on my list. Is there a way to clean it or do I need to just purchase a new one and install it? I will also check for any vacuum leaks. Thanks!

 

If it's the EGR valve, I would think it would throw a code.

 

You're right, it should. I guess that it's possible the thing could be introducing enough exhaust gas to cause the problem, but not enough to set a code. Probably not, but it can't hurt to have a look at it.

I'd try cleaning it first before spending $ to buy a new one. If you find a whole bunch of carbon buildup, you can remove it with some medium-grade sandpaper. There is probably a solvent on the market that would do the job as well - maybe Goof Off? Be sure to get a new gasket when you reinstall it.

Good luck!

 

Thanks for the info. I didn't realize the 302's had coil packs. All my Ex's have been 4.0's and all the 302's I've had in other vehicles used distributers. All that said, if your looking at cleaning the engine, try running Seafoam through the intake via the vacuum system, and use some throttle body cleaner on the butterfly valve and surrounding area. When you changed the IAC, did you spary and clean the ports into the intake. On my Mustang with the 302, it has had a tendency to get a little oil over time through the PCV that would gum up those ports and the IAC. Removing the IAC and using some throttle body cleaner worked wonders.

 

New symptom...persistent knocking noise coming from what seems like the front engine cooling fan. I had my husband come out to give me another opinion on the sound and I now agree with him. Could my fan clutch be dying?

 

Could be. With the engine off, see if there is any play on the fan shaft or the water pump shaft. Try moving the outer edge of the fan towards the rear and front and see if there is any movement on the shaft. There should be none. Also, see how easy it is to turn the fan. There should be some resistance. Lastly, if you're still not sure, with the engine running, take a rolled up newspaper and touch the outer edge of the moving fan with the opposite end of the paper from where it is being held. Obviously, be very careful about getting into the fan or belt(s), stay clear. If the fan stops turning when a paper is placed against it while the engine is running, the clutch is too weak. However, a bad clutch would typically result in an overheated engine, not really in a rough idle.

 

Thanks JerrySimm. I don't have the rough idle anymore. The new spark plugs, wires and Seafoam throughout (oil, gas, intake) have done the trick on the rough sounding idle. But now I can hear the knocking coming from the front part of the vehicle. I wonder if the clutch or fan was damaged when my husband and I changed my serpentine belt. There is a slight (1-2mm) of play in the fan (from front to rear only). It makes a sort of low click sound when it goes back and forth. The fan moves with a lot of resistance. When I try to spin it, it goes about 1 blade before stopping.

 

Check the other thread.