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quick question

is the TPS the same thing s the idle stablizer? How can I check to see if it working correctly?

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Old 10-21-2004, 02:36 PM
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NO actually............

The idle stabilizer is located under the intake manifold and the TPS is located on the throttle body.

Whats happening that you suspect either of these?
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Old 10-21-2004, 02:40 PM
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Which one do you want to see if it is working correctly?
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Old 10-21-2004, 02:44 PM
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They problems they cause when they fail are compledely different as well. What's not working right? Whad kind of symptoms do you have?
Old 10-21-2004, 03:36 PM
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I have an 85.5 944 so there shouldn't be any engine shudder, but there is. when i start the car it shudders and then stops at idle. It also shuddes whenever I let off the gas, the idle drops to 700 and then returns to normal. I'm positive this is not motor mounts. How can I fix this annoying problem?
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Old 10-21-2004, 03:44 PM
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Your idle-adjuster screw is too far in. Unscrew it by 2 full turns and the idle won't drop below 900rpm when you let off fthe gas.
Old 10-21-2004, 03:56 PM
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.... give that a shot.. You may find that if the idle is a little too high she will also start to hunt for idle.

The other thing you want to do when you set your idle is to bypass the idle stabilizer ......... So you have to rig a jumper wire for the test plug
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Old 10-21-2004, 04:04 PM
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"You may find that if the idle is a little too high she will also start to hunt for idle. "

That's why you want to make the idle-adjustment without disabling the idle-stabilizer. As you open the idle-screw , the DME closes down the stabilizer to maintain the same idle speed as before.

The reason you have the idle-drop below idle-speed and the recovery is that your idle-screw is too far in. So at idle, extra air is vented through the idle-stabilizer to provide enough air for 900rpm idle. So the split may be 70% idle-bypass around the throttle-plate and 30% from the idle-stabilizer. The problem with this is that it takes a fraction of a second for the idle-stabilzier to respond and open up when you let off the gas.

Then as you're driving along and let off the gas, closing the throttle, you're only getting 70% of the air needed to maintain idle, so idle-speed drops below spec. Then it takes a tiny time-lag for the idle-stablizer to open up and supplement idle-air, and the idle-speed recovers.

So what you're doing by unscrewing the idle-adjuster is to provide 100% of idle-air from the bypass only. Then the idle-stablizer stays closed at all times (exccept for cold-starts and AC operation). That way, when you let off the gas and close the throttle, you're getting 100% of the air needed for idle from the bypass, thus no more dropping & recovering idle.

The other thing to watch out for is intake-manifold leaks. The 4 gaskets or those vacuum hoses and tubes that come off the manifold can lead to leaks. Then you'll have rhythmic up and down hunting idle as the stablizer tries to open & close to compensate for the leaks.
Old 10-21-2004, 04:13 PM
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OK I'll give it a shot but I already tried re-adjusting the screw. The throttle is as far open as it can be right now. Can there be any other causes?

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Old 10-21-2004, 06:55 PM
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