nib5

I cleaned up the throttle body on my car and have now acquired a 1K idle. It starts @ 850 & works it way up to 1K as it warms up. There is no fluctuation and there are no mods to the engine. I have been reading up on it on the board but it seems that the ISV pushes it very high when faulty (C.2K+ or so). The vacuum hoses that were tinkered with when I removed the TB seem okay. Any bright ideas?

AutoXdriver

My idle jumped to 1200 RPM a couple of weeks ago. I had my local Porsche mechanic look into it when I had him reeplace the motor mounts and retension the belts. He did the same thing you did, however it only came down to around 1000, sometimes 900. I know it was around 800 before that. Hell at this idle RPM I could have left the motor mounts alone!

Der Cupmeister

The throttle stop switch might need adjusting ? DME might not think the throttle plate is closed.

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Travis - sflraver

both my 944's idle at 1000. I never thought that was a bad thing. what are they suposed to idle at? my 944na had a bad break booster and it made the idle jump to 1500 i guess to compinsate for vacuum. I replaced it with a used one off ebay and it came back to the usual 1000. both have chips so that could be a reason maybe.

Travis - sflraver

I saw where you talked about the throttle position switches on the throttle body above. There was a mod I was thinking about and I would like some feedback on it. When you open up the throttle position switch you see two micro switches and a small cam. One switch is for the closed position and the other is for the 3/4 to full open position. Would it give you any better response if you were to make that little cam so it hit the open switch at maybe half throttle rather than 3/4. What exactly does that switch tell the DME.

mxsav

O.K. nib5, I've got a 2400 rpm idle. What is an ISV and how do you fix it? Already replaced vacuum hoses and replaced the Y and T splits on my na in case they were bad. Still have 2400 rpm's at idle. Help!

Travis - sflraver

The way I tracked down my break booster problem was when I would press the break the idle would increase. somthing to check maybe.

nib5

[quote] What is an ISV and how do you fix it? <hr></blockquote>

Idle Stabilising (aka Control) Valve, it is under the intake manifold, between No.2 & 3 pipes. It has two hoses (a tap into the big hose just after the Air Flow Meter, passing through the valve and ending up joining the underside of the IM near the No. 4 pipe), and two wires going into it. It changes the airflow into the intake manifold at start up before the engine warms up. It can sometimes get stuck. You have to take the intake manifold off to get to it (bravo! designers - slow hand clap). Some people have had success cleaning it, otherwise it has to be replaced. The F1 idle speed you have is a symptom of a fault in it.

Toolmaster

Cool thread here!

Ok - idle in our cars. This will focus on the Turbo's BTW.

Idle should be (all things being equal and I'm talking a STOCK car here) around 840 +-40 rpm. Chips shouldn't mess with the idle, though highly modified cars with things like fuel computers, etc, might.

There are a couple things that can effect the idle.

1) TPS sensor. With the car OFF, gently move the throttle plate and listen carefully. You should hear a click from the TPS as soon as the throttle plate starts to move. If not, adjust your TPS till you do, or replace it if it's not clicking. To adjust it, loosen it in it's mount, and rotate it till you just hear a click when you open the plate. Lock it in place, and re-test. You should be able to just open the throttle and hear the click.

2) Vacuum leaks will increase idle speed. Here's a trick for you. Get a fuel filter for your car (when was the last time you changed it anyway?) and CUT IT in half. I typically replace the fuel filter, then cut the used one in half. After allowing it to dry and insuring there's no gas in there of course.

Remove the fittings from either side, and insert a tire valve or an air chuck in there. You'll notice that on BOTH ways it fits perfectly. Then, remove your air cleaner and AFM assembly, and find that the fuel filter happens to be a PERFECT fit into the J boot. Pressurize your system to about 7-8 psi, and spray a mixture of dish soap and water (50/50) on all of your vacuum connections. The ones that bubble leak. Fix them all. Don't forget to hit the idle screw with some soap, I'll bet that it's leaking if it hasn't been replaced recently. This will also find all your boost leaks. If you wanted to, put a wet rag in the exhaust at the same time, and you'll also find all your oil leaks and exhaust leaks too!

3) ISV circuit. The Idle Stabilizer circuit can be disabled by bridging two pins in the test connector for the KLR. The two pins to bridge are "B" and "C". "C" is the one all by itself, and "B" is 2 pins over COUNTER CLOCKWISE. Jumper these two pins with a piece of spare wire, and use the idle adjustment screw on top of the throttle body to move the idle to the 840+-40 range.

If you test and do these three things, most idle problems will go away. Of course there are other potential items, like a fuel issue, or ignition issue, but this should take care of MOST of them.

HTH!

my944

I had an idle that stayed at 1200 after the supercharger was installed...dumb a** told me that was "normal". Caruso Motorsports in Westport, CT has no clue.

nib5

Surely with a supercharger, some adjustments would have to be made to accomodate the extra airflow - even at idle there would be something coming off the blower. As there was no sc 944 from Porsche, I guess the rule book is sort of torn up.

mxsav

Toolmaster! what is a KLR and where is it located? Couldnt find it in the haynes (like I thought it would be in there!) manual. My idle is still at 2400 RPM'S and I dont want to take off the intake just to test the ISV circuit. Just recleaned the AFM and the TS and replaced all the vacuum lines and the RPM'S are still 2400! <img src="graemlins/crying.gif" border="0" alt="[crying]" />