Ldorris

2001 S600 i'm sorting out. OBD2 throttle position starts around 5 but only goes to 37 even at wide open throttle (performed test both with car running and also just the ignition on but car not running). It also seems to drop quickly to the 16 range while holding WOT. Thought this should be 80 at minimum. RPMs only go to around 4000 and then stop climbing. Runs pretty good below 3000 rpm (after a restart with no misfiring). Idles smoothly at 650 rpm.

Other symptoms are lack of acceleration and occasional misfires that often disappear with a restart. New MAF, plugs, vacuum lines, 02 sensors on bank 2, vacuum is 19" hg at idle, no codes (when not misfiring).

Car is a rescue attempt... bought it with plugged PCV venturi and smoked like crazy. So, could it be a clogged cat? Bad throttle position sensor? Throttle body? Fuel filter?

wallyp

The computer does not think that it is a good idea to blow the engine, so it won't let you do it by over-revving in neutral...

You can check for a partially-plugged exhaust by hooking a vacuum gauge to manifold vacuum. While watching the vacuum gauge, rev the engine to 2500, and hold the throttle absolutely still in the same position. The vacuum should drop as you pop the throttle open, then stabilize at a reasonably high reading and stay there as long as you hold the throttle still. If the reading drops with opening, then stabilizes at a high reading for a few seconds, then starts slowly dropping, the exhaust is partially plugged.

Ldorris

But I'm not over-revving the engine if the engine isn't running. The sensor still gives throttle position with just the ignition on but not started. Does the car being in park automatically restrict thr throttle position, even if the engine is off?

I performed the vacuum test... holds steady, doesn't drop.

tusabes

ctravis595

Ldorris

Thank you. And i think you're onto something with the cats... going to attempt unbolting them and see if performance improves.