I started up my 04 Marauder yesterday, it started and ran like normal, however the rpm's on the tach were very low. It didn't sound like the engine was running at 250. The oil change is less than 500 miles old, the dipstick was on the full mark. There were no odd noises from the engine, just the tach showing the low rpm's. The engine rev'ed like normal, but it would return down to under 500. The car has an unknown tune from the previous owner, 4.10's, k and n intake. Any help or ideas as to the cause would be greatly appreciated.