Status Update, Fast Idle - put to bed finally Options

[lsintampa]

75 2.0L D-jet

Hey guys, it's been a while but I thought I'd just sort of give a status update on my car.

I had a number of posts about fast idle, surging, hunting, and other sorts of D-jet issues, but now that I've had my MPS rebuilt, replace the TPS board, etc. etc. and also went to school (thanks to those that offered their expert advice), I'm happy to report that I finally am happy with where I'm at.

A while ago I asked why some throttle body plates have holes in them and others do not. Well I still don't know, but I have a pretty good theory which is this:

My car had dealer installed A/C - which some PO removed a long time ago so it's long gone. I think that when the dealers installed A/C, they needed to adjust idle settings for the compressor being an added burden on the motor. Especially when the clutch engaged. So what I'm thinking is they replaced the throttle body plate, with one that had a small hole in it. This would cause the car to idle faster without mucking with the air bypass control.

In any event, I have no way of knowing if that's a valid theory or not, but I can tell you that I took the plate off and soldered up that hole, and my idle is now manageable!!!

Curious if anyone knows if this makes any sense. I talked it all over with a fairly good Porsche guru and he thinks it does. Again, no way of knowing but the results of closing up that hole has made a big difference.

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Thanks to all that got me parts and schooled me - you all know who you are!!

Len

[Dave_Darling]

Many cars without AC also had holes in the throttle plate.

--DD

[lsintampa]

Many cars without AC also had holes in the throttle plate.

--DD

I thought that may be the case. I just don't know what function it serves and why on some and not others.

The AC theory made some amount of sense.

Do you have an idea why some do / some don't??

[r_towle]

Aliens.

[yeahmag]

I wonder if the throttle shaft itself is worn and air is bypassing the throttle plate more than normal...

[JamesM]

Many cars without AC also had holes in the throttle plate.

--DD

I wonder if the throttle body difference is based on the CCV setup used? Early cars oil tower vents to manifold vaccum which would potentially allow more air past the throttle plate at idle, later cars vent to the air filter so perhaps a small hole was needed in the throttle plate to compensate?? Just a theory.


My guess is the hole in the throttle place is not the actual problem here though.

[914Mels]

Way back when, I had a single center carb system on our 914, the combo of carb and cam wouldn't allow me to get a high enough idle speed without really cranking the idle adjuster screw. This created a problem with the transition port in the carb as the throttle plate was open more than designed just for no load idle. to fix it I drilled a 3/16" hole in the throttle plate to create more of an air bypass allowing the throttle plate to stay in it's normal idle range. Obviously the carb was not matched well to the application but it is what I had to run with at the time.

[lsintampa]

IDK,

I've yet to have anyone tell me why some plates have holes and why others are without.

That said, and all that I know is that my car HAD AC, now it does not. Rebuilt motor and just about everything else and it wanted to idle fast. YES, valves adjusted, no leaks, good MPS, good TPS, good aux air valve, good timing, good everything. Still fast idle.

Solder up that hole - everything else being equal - good idle.

End of my story.

BUT anyone have any clue why some plates had holes and others not???

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