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

[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.