My 05 base model makes a fair bit of rattling noise on startup and im reasonably certain its coming from the timing chain. but before it tear it open to fix id like to know what type of tensioner it has hydraulic or spring?

If its hydraulic i suspect the o-ring in the tensioner is shot and i can rebuild the tensioner with new o-ring. if its spring then ill be ordering a hydraulic one from crate engine depot.

**EDIT** thought i should mention it only does this if its been sitting longer than an hour and only does it for 3-5 seconds, that's why i suspect the oring

 

reach back and feel the massive bolt head for the tensioner (back passenger side of engine just below the valve cover). If it is flat then it is spring, if it has a hump in the middle of the head of the bolt then it is hydraulic (someone correct me if I am wrong). i believe based on year it should be hydraulic

 

i believe the only one available is the hydraulic one due to the old one failing and GM discontinuing the production of the part.

 

I have a similar issue with my chain. I am also getting problems when I slow down the car to come to a stop the rpms go crazy like from normal to under 500 rpms then back up and so on until i stop and the car almost stalls. Im not sure what this is based on the fact im not getting any codes. It's very strange. I cleaned the air intake and sensors and it helped a little. But not fixing it totally. I think my chain may be related.

 

idle air control?

 

Hum it might be that, i have tried cleaning out the whole intake system and that helps.

 

I wound up just saying screw it and ordered the upgraded tensioner.

I had the problem on my grand am. most likely its something to do with your IAC. It could also be the Manifold air pressure sensor i suppose. If thats misreading the pressure by a little then i could cause that without throwing a code. however that doesnt seem as likly

 

Idk about the 05's, but my 07 L61 (no IAC) does the same thing because of an exhaust leak at the exhaust mani. Just to lazy to fix it. Lol

 

Gonna add a second post because my "smart phone" won't let me edit ... I have the upgraded timing tensioner, tac takes care of idle air, and I know it's at the mani because after replacing the cheap gasket that came with my header (header install is when it started) with the GM mls gasket and tourqing properly, the sound came back eventually. Cheap header, cheap results for me. And my ltft's bounce +3 to -3 constantly.