I’ve been researching the boards for the past few days to gather most of the info I need, but I further input would be appreciated.

Background info: Keep in mind I have had no CEL’s or engine issues. Several days ago we had our first cold snap. It got down to 20 degrees C. That morning I cranked the engine and it didn’t start right away like it normally does. I cranked it a couple of times and it finally started. I let it warm up a few minutes and went on my merry way. Same issue for the following 2 days, including the cold weather. On day 4, I cranked the truck and it started to make a slight grinding/scraping/rattling sound. I popped the hood and it was coming from the front of the engine. The sound disappeared after about 3 mins at idle and the CEL came on. The sound didn’t come back all day. I had the CEL read and it was P0135. I bought a Bosch OE style oxygen sensor today and replaced it. The CEL is gone, BUT the noise at cold start up is still alive. The sound is obviously temp related since it disappears once it warms up. I don’t have any performance or idle problems. Actually, the new sensor helped smooth the idle a bit. I currently have no other codes.

To do:
-Change plugs
-check for IMG leak, but I don’t think that’s the cause from reading other posts. doesn’t sound like a vacuum leak.
-replace PCV
-check vacuum hoses
-clean MAF
-clean EGR

Possible causes of sound:
-bad IMG
-failing tensioner
-bad/loose belt

Any input on other things I should inspect to determine the source of the sound? Again, it doesn’t happen while I’m on the road just at start up. I THINK I heard it as I was pulling into a parking lot tonight so it might be getting worse.:banghead: :banghead:

It could be something as simple as a loose heat shield (very common).

I have an odd noise with mine too once it is below 20C. Lasts for about 3 minutes and in gone. It has done this for about 3 years now. It doesn't make a peep in the summer.

What does a failing tensioner sound like? I might have to get a sound clip of my truck.

Keep tabs on that thermostat - could be the waterpump; that's when mine failed was during a VERY cold artic system that swept through.

Mine made funny scraping sounds for 2 days, by the 3rd day, at -15F, it peed out.

Could also be your alternator.

And, like Amigo said, could also be simply the cold weather.

it sounds to me like a bearing on the front of the motor? such as idler bearing either on the serp or timing belt. or bearing on the alt or like ramblin said the water pump.you can't rule out the compressor either. my 2000 does the same thing when it is very cold out. it is one of those bearings (in my case) making noise. once it warms up in my case it is fine.

p.s. how did you fix the cel for the trans? mike

it sounds to me like a bearing on the front of the motor? such as idler bearing either on the serp or timing belt. or bearing on the alt or like ramblin said the water pump.you can't rule out the compressor either. my 2000 does the same thing when it is very cold out. it is one of those bearings (in my case) making noise. once it warms up in my case it is fine.

p.s. how did you fix the cel for the trans? mike

yup that sounds right. I'm sure if I had an automotive stethoscope I could listen to it while the engine was cold.

Guys,
One thing I noticed of my Rodeo in cold weather was the idler pulley on the front of the motor on the serpentine belt. Mine was going bad (bearing inside the pulley) and once we got a good cold snap 40 degrees F, it made a grinding/screech at Idle and 3000 RPM, and would fade once the engine warmed up. (I guess the metal would expand?) Anyway, that was a cheap $20 replacement and voila, sound gone.

-Scott

My truck made a screech for a couple days before the alternator went bad. You've got a hard start, too. Check your voltages...

Well, it didn't make a peep today. Todays' high was in the 60's and lows in the 40's. I hate diagnosing noise issues b/c it just takes too much time and possibly money on unnecessary parts.

It's almost down right impossible actually - to find the noise. Sometimes, the noise is simply caused from the cold itself; I know my truck creeks/rattles and the tires thump around for the 1st couple miles when it's +15F or below.

My point is there really isn't anything you can do, because there's probably nothing wrong, vehicles can sound creepy on real cold mornings.

Perhaps the noise is the fan clutch, or the fan itself making contact with the shroud. The extra high idle at a cold start-up might be all it takes to extend the fan to the point of making contact? Thought I'd mention it because it's fairly cheap and easy to fix that.

Thanks for the ideas gents. I'm still trying to figure it out, but it hasn't made a peep since I created the post.

I may just have to wait until something actually breaks. :banghead: :banghead:

At least finals are over.:wink:

I haven't forgotten about this post. I've narrowed it down to the serp idler pulley. It has progressively gotten worse. I will replace and update.

if you can get to the backside of the pulley. hit it with some spray lube just to narrow it down. should quiet right away when you find the screamer.

Well, I finally got it repaired. It was the idler and it made a loud crunching sound as I was headed to the mechanic this morning. I stopped and popped the hood to find idler in bits and the belt slightly torn. I'm kind of glad it finally exploded. Total cost: $ 70 (parts and labor). THE END.

Cool! Thanks for the update.