air meter and throttle body

[todd84944]

Using a volt meter does anyone have the correct readings for the air meter and the throttle body, testing them off of the car. I did not have the na shutter untill I took the throttle body off to clean it. After putting everything back together I had the famous up and down idle. I took the throttle body back off and ajusted the throttle position switch out to just before you feel it "click". The up and down idle is gone, but the car is idle at about 1100 rpms. I relize ajusting the throttle position switch made it idle higher. But why did the up and down idle start after I took the throttle body off and cleaned it. The car is running great, just idles at 1100. My prized toy is a 84.

[divezic]

There is a screw on the throttle body that acts as an air by-pass which sets your idle speed (not the throttle position switch).

Let the engine warm up to normal operating temps. If you are idling at 1100 then turn the screw down slowly until you get a constant 900+/-50rpm.

[SoCal Driver]

Search the archives. Been posted before -- many times.

[Porsche944]

You simply un-did the previous owner's "fix" for the "944 Shudder."

The problem is with the timing the DME uses to approximate engine slow down when the throttle is closed.

What happens is when the throttle is closed, the TPS sends a closed throttle signal to the DME. If the engine RPM is above a certain value, the DME assuemes a trailing throttle condition and turns off the fuel injectors. As the engine comes to a normal idle RPM, the DME is supposed to turn the injectors on.

However, the engine slows down faster than the DME is programmed for, so the idle falls below normal. The DME turns the injectors on, causing the engine to shudder as it comes back to idle.

Another "symptom" of this maladay is a hunting idle. In this case the idle speed is set too high. The DME sees the high idle and cuts the injectors. Idle falls and the DME turns the injectors back on.

Apparently all of the early ('83 to '85.0) 944 engines will do this.

You have a some options:
1. Set the TPS so the throttle closed signal is never sent to the DME.
2. Get a "Shudder Fix" from F.R. Wilk
3. Replace the stock DME and Air Flow Meter with parts from an 85.5 or an 86. You have to replace both the DME and AFM because the early AFM is not compatible with the later DME.

I have done all three of these. #1 is not really a fix, but is more of a work around. #2 is a permanant fix, but you need to have the proper soldering tools and skills. IMHO #3 is the best fix.

Replacing the DME and AFM is basically plug and play. You may need to adjust the engine idle a tad, but that's no biggie. One major upside is you can use a performance chip.

Hope this helps.