928GT8108

Dear members,

My 928GT having the subject issue. Sometimes when i need to shift down the gear (example: 3 to 2), once i press the clutch down, the rpm will drop down so quickly close to 0 rpm and lead the car stall. I have to restart the engine immediately, since all the elecetronic are off too. Anything i have to check? I already check all the hoses and replaced the throttle position switch.

John Speake

What is the idle speed with the car in neutral ? Does the idle speed hunt around at all, or is it constant ?

FredR

When you replaced the switch did you adjust the position such that the idle contact was functioning correctly? It is a very subtle adjustment and does not take much to get it off. you cannot simply unbolt the old and pop in the new and expect it to work correctly if that was what happened.

It is a very fine adjustment and if it does not click and make/brake contact immedately the throttle moves off rest/back to rest position the ISV will not kick in and the engine will stall.

Also, if you had the inlet off, are you sure you connected the ISV connector correctly? It can be difficult to get that thing to seat correctly and if that is not connected properly the ISV will not work

Regards

Fred

Ducman82

^^^^^ i had to sit and "listen" for the switch to click then tighten the screws when setting for idle.

WallyP

Quick check for the throttle switch:
- Change the dash to read the fuel economy.
- Drive the car at highway speed.
- Release the throttle almost all the way and note the fuel economy.
- Take your foot completely off the throttle and note the fuel economy - make sure that the road speed is high enough that the engine speed is still above 1500 RPM.

If the throttle switch is adjusted correctly, and the wiring to the ECU is good, there will be a major difference in the fuel economy between the two tests. If there is no difference, the switch is not functioning correctly, is not adjusted correctly, or there is a wiring problem.

928GT8108

The idle speed in neutral is about 950 and it is stable. The only problem is when driving shifting down gear. Once i press the clutch, the rpm will drop it so quicky.

928GT8108

May i know what is ISV?

928GT8108

Will try it later when available.

FredR

Idle stabiliser Valve- it modulates pilot air flow to control the tickover speed.

If yours ticks over at 900 rpm when it is warm then something not right- usually an air leak for that symptom.

As to why the revs should die when changing gear no thoughts to explain that one at the moment.

Fred

928GT8108

Oh, that parts just replaced it 3 months ago.

Alan

Since you have a 1990GT with a digidash - you can modify Wally's procedure to be really much easier. If you are driving at say 50+ MPH you can set the digidash center display to instant fuel economy mode (MPG) mode and take your foot off the gas. If the idle switch engages properly you should see fuel economy of exactly 90MPG (a default max). This is the overun fuel cut-off mode - it only happens when the TPS switch is in idle mode. Same test just easier to do...

Alan