LongARM

I need some help from the experts Please. Replaceed blown airbox over the winter. first start-up here in Canada was March 13. It start right up, but idle went 4000 rpm and won't come down, i have searched on here and no similar complaints.
Have double checked all lines and components.

LongARM

Sorry it's 1977 911s 2.7l

rusnak

I don't have a CIS, but did you check to see if your throttle is closed? It sounds like there may be tension on the throttle lever, or it may be held open by something that was moved during the airbox install.

LongARM

i have checked linkage, throttle plate.etc,idle setting turn in cw.when i press accelerator it jumps to 5000 then back downto 4000 when i release it.

rusnak

I am not completely sure, but from my college days, my old BMW had a plate that needed to rest closed. If this plate inside the intake plenum is raised, then the throttle would rise as you describe. Perhaps this plate is not closing inside the intake plenum (sorry I don't have a workshop manual at work, and I can't remember what it's called).

theiceman

okay slow down here ... lets look at it logically ...

Assuming you have replaced a cracked airbox you have changed your mixture. an actual bigger factor for idle is the mixture more than the idle screw.
did you check your CO after your airbox replacement ?
Mine idled low right after I replaced my air box and I had to back increase the idle setting. when the engine warmed up and I put the AFR meter on it and i tuned the CO the idle went way up and I had to readjust the idle. it was a bit of playing back and forth till i leveled it out.

Also did you check for the 1mm gap for the air plate as in the service manual. Also verify you have the WUR plugged in. the heating element will close off your fuel pressure and reduce your idle .

If it idles smoothly but high it sounds like you just need to make a few adustments.

LongARM

Thanks iceman, wur is all connected,air plate is smooth and has proper gap. Fuel mixture makes sense , i will check that tonight. ccw to decrease cw to increase.?? i have no CO meter yet.

rusnak

cw richens, ccw leans.

Isn't the airbox upstream of the airflow plate? In other words, the airbox is not a source of unmetered (false) air, is it?

The idle screw is an air bypass screw, and it sits on the throttle body. It lets air in, but that air is also metered by the airflow plate.

theiceman

absolutely the airbox is downstream of the plate. The airbox is actually a plastic intake manifold atached to alluminum runners that atatch to the head.
i would not recommend messing with the idle mixture without a AFR meter . Either borrow one or pay a mech a few bucks to set up your final mixture. Too bad your in kingston. A renlister in TO has one I borrowed to set up mine. If you get it wrong and lean it out to much , gues what , you just ate another airbox/ I just did mine this time last year and it was a really enjoyable project. I imagine you replaced your throtle bushings and other while your in their projects.
if your interested search air box replacement by me as I outlined my whole process. The critical part as you have found out is getting those damn rubber sleeves to line up and sealing the runners square to the head, and of course the final mixture.

Good luck.

PS Markus Blazack lives in Kingston and although he is a 944 guy he will for sure be able to help you out.

LongARM

I tried decreasing fuel mixture a few clicks, no luck still racing to 4000 rpm at start-up. Just trying to get a proper idle at this point, will fine tune later. I replaced throttle bushings ,intake sleeves ,gaskets and all vacuum lines while doing airbox. Would timing allow it to go that high..?

rusnak

is there a vaccum actuated fuel pressure regulator, or cold start valve? Just throwing stuff out there, since I don't have a manual.

LongARM

been over everything, is it possible to get the air baffle in throttle, in wrong..??? Does anyone have a photo of the top view of a throttle body.???? (77 CIS)

Brett San Diego

4000 seems way out of whack. Major air getting around the throttle somewhere or the throttle is open. Even if the AAR is stuck open, that only gives about a 1200-1500 rpm high idle (normal cold start rpm), and that's a sizeable auxiliary air supply bypassing the throttle. I couldn't imagine a 4000 rpm high idle from "casual" air leaks or typical part failures. I guess I really don't have any help, except to say double check the obvious: massive air leaks, throttle stuck open...

Do you have cruise control? I had a high idle problem that I finally found was the cruise control cable not allowing the throttle to return to fully closed.

Good luck with it and let us know the resolution.

Brett

autobonrun

+1 on the open throttle. Make sure the linkage in the engine compartment is allowing it to return to the low position. See if movement by hand lowers the rate.

theiceman

I am not at home so don't have any pics handy but if you searched my thread yo should see some. You should be able to take the kidney boot off for closer inspection with everything still in the car. did you check for proper throtle closure before reinstalling the CIS ? if that plate is resting at 1mm with hte engine off make sure your butterfly is closed check with a dental mirror.