Hillsborough County schools get out May 25 for the summer break. ChaCha on! 7 years ago
Â· just now. Report Abuse. A cast iron manifold will expand and contract, the JB Weld will not. I think JB Weld is fantastic stuff (have some as we speak) but not for a cracked exhaust manifold.You can always check out their website: http://jbweld.net/index.php I only have experienced JB with cast though, if your manifold is another material you may get lucky.ource(s): Q: Will J-B Weld work on an automotive exhaust? A: Because of the extreme temperatures of exhaust systems, we do not recommend J-B Weld for use on exhaust manifolds and catalytic converters.
Your IAC {idle air control valve} could be going bad, more then likely its just a vacuum leak. Get a can of carb cleaner and spray lightly around the intake and vacuum hoses. If you hear a change in the engine RPMs or idles different, you found the leak. If no change, IAC valve should be replaced. You can probably go 35 on idle speed,as far as the fluctuation goes add a fuel additive to the fuel,preferably when your tank is low on fuel. Sounds like a vacuum leak, maybe one of the components or one of the hoses at that age of the car. Have the engine computer codes read, they may reveal teh problem.