Ok, I just got finished rebuilding my 420a. Timing is set to TDC, I did double check it. It starts fine but idles at 1000-1100, then climbs to 2500rpm and stays there. I checked the tb, and if I cover the opening completely it stalls. The is a hole on the bottom of the tb inside the intake hook up which I beleve goes to my IAC. When I put my finger over this hole is starts to die but right before it stalled I moved my finger and it stayed at 1100 rpm, first question is, is the hole going to the IAC? Or is it to another sensor? Next is with the 1000-1100 idle, I have high compression pistons, would this make the idle change to be that high or would that be a vac leak? I have searched but cant find anything in the forums like my problem. Please help if you can, I also have no Idea how to check for vac leaks, I read about the gauge you can get but I dont have a lot of extra cash, any way to check it with out the gauge?

Originally posted by EclipseGS45150
There is a hole on the bottom of the tb inside the intake hook up which I beleve goes to my IAC. When I put my finger over this hole is starts to die but right before it stalled I moved my finger and it stayed at 1100 rpm, first question is, is the hole going to the IAC?

Yes, if your car was down for a while, you may want to just unbolt the TB, and clean the IAC and its passage out. It's pretty simple There's a write-up for this on the main page under the maintenance section.

Originally posted by EclipseGS45150
Next is with the 1000-1100 idle, I have high compression pistons, would this make the idle change to be that high or would that be a vac leak? I have searched but cant find anything in the forums like my problem.

This IDK someone else could help out I'm sure

Originally posted by EclipseGS45150
I also have no Idea how to check for vac leaks, I read about the gauge you can get but I dont have a lot of extra cash, any way to check it with out the gauge?

I believe you can just spray your vaccuum lines with carb cleaner and if there is a leak when you spray it, there will be a noticeable change in the idle

Also if you really don't want to actually check your vac lines, you can just replace with all new since they're cheap

I was thinking about replacing them also, do you think the silicone type you can get from autozone will do just as good a job?

Originally posted by cs82685

Originally posted by EclipseGS45150 There is a hole on the bottom of the tb inside the intake hook up which I beleve goes to my IAC. When I put my finger over this hole is starts to die but right before it stalled I moved my finger and it stayed at 1100 rpm, first question is, is the hole going to the IAC?

Yes, if your car was down for a while, you may want to just unbolt the TB, and clean the IAC and its passage out. It's pretty simple There's a write-up for this on the main page under the maintenance section.

Originally posted by EclipseGS45150 Next is with the 1000-1100 idle, I have high compression pistons, would this make the idle change to be that high or would that be a vac leak? I have searched but cant find anything in the forums like my problem.

This IDK someone else could help out I'm sure

Originally posted by EclipseGS45150 I also have no Idea how to check for vac leaks, I read about the gauge you can get but I dont have a lot of extra cash, any way to check it with out the gauge?

I believe you can just spray your vaccuum lines with carb cleaner and if there is a leak when you spray it, there will be a noticeable change in the idle Also if you really don't want to actually check your vac lines, you can just replace with all new since they're cheap

For the high idle it sounds like you have a vacuum leak, check and recheck all hoses and connections and do a leak test.

I checked the vac and no leaks, I found the wires on the CTS needed redone so I did that and now it idles about 1000, but if I give it gas then let go it slowly goes down from 2000 and almost dies???

What compression pistons? What else did you do upgrade with the rebuild?

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