93 SL2 automatic

Hey guys and gals.
My 93 has been making noise for quite a while now. The actual noise maker is the surpantine belt tentioner. All is ok with the tensioner. Everything is tight and tensioner is only a few months old. As the engine is loaded down, a/c on, sitting still in gear with foot on the brake, the tensioner rattles against its relaxed position, ( the position it would be in without a belt). RPM`s fall to 500 , this is when the rattling begins. When I remove foot from brake or take car out of gear rpm`s increase and noise ceases.
Question? Do I have a belt size problem, or is the problem with the engine managment system. IE. Improper rpm range. ?
I always thought when the a/c is engaged, engine rpm`s should increase. But it does not. thanks for your help in advance.

You might have two problems. I cant imagine the serp. belt would have ANY effect on the idle, so you might want to do a search on this forum about idle speed, and see what the experts think. Im guessing it could be an idle speed control valve, or bad Engine Coolant Temp sensor, or?
How do you know the tensioner is getting to the 'relaxed' postion, as if the belt were too long? It should be held several degrees away from that position by the belt. With the engine idling as low as 500 rpm, there are going to be things rattling that normally wouldnt, because there is so much variation in the crankshaft speed when running that slow. I can imagine the timing chain is seeing slack on the 'tension' side, due to the camshaft being turned that slowly.
When you turn the a.c. on, the engine should get slightly more air coming in (to compensate for the a.c. compressor load), thanks to the idle air control valve, which is controlled by the PCM. If all is working well, I would think the idle speed should remain essentially the same, with the a.c. on or off......and that speed would be more like 800 rpm.

While I had the passenger side wheel off and the plastic covering removed, I had a direct view of the Idler. I was just finishing an oil change and figured I would take one more shot at this.
I removed the belt,marked the Idler housing, reinstalled the belt and noted the distance between the marks. While running vehicle under the loads mentioned before, the rattling happened every time the marks came together. Olso I used a serpantine belt tool to put a slight load on the tentioner during this test and quietened it down. I would not suggest for anyone to do this. There is a lot of things turning under there!
I believe your right. The engine should maintain an rpm range at idle no matter what is on. The PCM is not being told by its sensors. Now I have to find out which ones.

Clean your Idle Air Control Valve on the Throttle body.
Replace your Engine COolant Temperature Sensor with a brass one. Your car has two, you need to replace the one with the 2-wire connector

Idle should be 800 rpms at normal operating temperature.
Idle should NOT change regardless of a/c or alternator loads.

Your tensioner should not be near its position with the belt off, when the belt is on. If it is, you have a bad tensioner.
Also, when playing with the tensioner, the bolt that one would grab on to to release tension and get the belt off sometimes gets loose in the process. THis then allows the wheel to vibrate back and forth thus rattling. Removing the tensioner, putting it in a vice and torqueing the bolt back so the wheel doesnt rattle is all that is needed :)

Hey thanks! I will give this a shot this weekend. It will be nice to sit in traffic without all the people staring with dissapproval. After this I need to tackle the leaky sunroof. I think there is enough imfo about this job in past forum discussions.:grinyes: