constant 4000 RPM after engine install

Well, I just put the engine back in a 96 sl2. I replaced a couple of sensors while it was out. now the thing only runs at 4000 rpm? any ideas? thanks.

DOHC or SOHC? what was done to the engine when it was out? rebuild/replace? more info the better. but start by checking for vacuum leaks, check intake manifold gasket, injectior O-rings, vaccum hoses, throttle body gasket(been known to drop out of place during install before), IAC, throttle plate fully closed.

Check idle air control activator/motor/valve. It's on the throttle body, below the position sensor. If it doesn't move, the rpm will be what ever it's stuck at. If you can move it all the way out, your engine won't even start without stepping on the gas.

well, i don't think its the air idle control thing. it was plunged in but i pulled it all the way out and it still runs at over 4000 rpm. thanks any way. i'm dreadin' the intake gasket. oh... its a dohc sorry. does anyone know how to run the computer check (if you can without a code scanner)?

with 96 and up a scanner is needed. i also forgot to say buy a can of carb and choke cleaner. with the engine running spray it in the areas of a posible leak. the rpms will drop when you spray near the leak.

Does it make a difference that i do not have the belt on?

will no belt cause a 4000RPM idle? no
will no belt cause problems? yes, namey no alternator to charge the battery and no water pump to cool the engine. do not run the engine without the belt, you risk major engine damage.

yeah, it only ran for 30 seconds at a time... well, on to the intake i guess. what do you suppose the odds of replacing the gasket with the engine in are?

its been done in under 45 minutes, so i'm told, book time is around 5 hours.

that gives me hope. i'll start it nov 4. i'll keep you informed. thanks again.

it actually might make a difference that the belt isnt on. One word, LOAD. The Idle Speed Control accounts for all the accesories that would be driven by the engine. Its giving the engine enough air and enough fuel to drive all the accesories but there is none of that load on the engine. Since the xtra power it gets to drive the accessories isnt driving the accessories, the energy isnt wasted, it just idles higher. the energys gotta go somewhere, it doesnt just disapear. Plus i dont recommend ever running an engine without a belt. its just not that smart. you need all the accessories for the car to run right. You just might screw something up if you dont think about things before you do em.

yeah, i know, thinking back on it all though, the belt was on initially, but it still ran much too fast. the water pump was leaking a bit so it has been removed to be replaced. from time to time, i'd start it back up for ten seconds at time or so... with out the belt... i think i will have to elimenate the intake gasket as a possibility first, then i'll get the new water pump on and belt and go from there i guess.

Check all your vacuum hoses and make sure there is no cracks or make sure there isnt one missing. Sometimes that can cause high idle but i never heard of 4000rpm cause of a vacuum hose. Make sure all your sensors are plugged into the right places. You get all kinds of symptoms when you leave sensors unplugged.

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Does it make a difference that i do not have the belt on?

I think you should always wear the seat belt........

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