have seen this problem posted multiple times, but never a solution. I stumbled on the answer after widening search to whole web. During warm up, the exhaust valves expand quickly and can stick open, causing rough idle, loss of power, check engine lights. when valve guides/heads heat up to match, engine runs normal again. I put new valve springs on just exhaust valves and engine ran normal for 6 months , then started to relapse. new springs were just stock aftermarket replacement springs. are there any better valve springs than stock that will fit the 2.3l engine?