high intial start up rpm and engine rattle

[rick herrick]

I have a 96 3.8 and often but not always the engine will have a momentary engine rattle that lasts for 4-5 seconds and then go's away. The problem is in my opinion the extremely high rpm start up (1900rpm) that the engine does after the engine starts and the engine starts almost immediately after the engine is cranked. I have been able to stop it if I delay the starting of the engine (I installed a fuel pressure switch), but it is not practical to crank the engine for 5 seconds in the morning. I'am not sure exactly where the noise is coming from in the engine, but the noise on morning start up usually occurs mainly after I do some highway driving for 2-3 hours, and then the following morning the noise occurs. The noise strangely will slowly go away if I revert back to my normal daily driving pattern of 7-10 miles stop and go. This is the second 3.8 engine that the car has had (the first changed under warranty for the same problem) and after 8-10,000 miiles on the new engine the problem is back. I told the service manager that unless they solve the initial high rpm (1900 rpm) start up issue the problem is probably going to come back, he didn't seem to concerned about that and it wasn't addressed. When I went back to the dealership with the same problem (engine rattle) he now say's that is normal, of course the car is out af warranty now, and I'am sure that had something to do with his statement. First of all, does anybody else experience this problem with their 3.8 camaro? Second does anybody have any solution as to lower the initial start up rpm? After maybe 2-3 seconds the engine rpm does drop and fast idle's properly @12-1300rpm until the engine is warmed up. I have tried to fool with the IAC motor as I have in the past on other cars I have had, but with this OBD 2 computer it reverts back to the original setting, which is that stupid high rpm. With the older OBD 1 computer you could adjust the IAC motor to the desired fast idle number you wanted and it would stay there, but not with this system. I have checked the throttle body for leaks and have set the throttle plate also, to no avail. I believe the problem is probably in the computer mapping, but only a guess. I have had a scan tool (tech 1) on the engine several times and everything seems fine. I'am a school bus mechanic, not a chevy wrench so I don't have access to their equipment or their tech representatives. Being that both engines had and have the same problem I have to think other owners of the 3.8 engine have this problem also. Any thoughts? Does anybody have any good clues as to what the engine noise is? My guess is maybe rocker arm. I do use a good 5-30 oil (not systhetic though). Why is the problem not consistant, and finally does anybody have any opinions on how I can lower the initial start up rpm? I know this is rather lengthy but it required me to fully explain the issue. It took me some time to just find a web site that MAYBE people might be able to help, the dealerships are of no help and the 800 number for chevy service complaints is a joke. Thankyou, Rick Herrick