I just installed new throttle bores with slightly larger bores/butterflies from CFM. Along with matched-flow injectors, I really like the improvement in my '92 TBI. What's hanging me up is that the idle is unnecessarily high because the butterflies want to be open more than closed. They actually don't completely close so I installed another return spring that brought the idle down from way too high to just too high.

The other issue, and the one I'd appreciate some feedback on is that the idle is obviously adjustable upwards using the "hidden" adjustment screw, but in my case the adjustment screw isn't even touching the pivoting lever. Thus, there seems to be no way to adjust the idle downward. Is this true?

Thanks. Dave

 

You should be able to drill through the tb and get to the idle screw. There is a thin piece of tin or something and right behind it is the screw that is a star fitting if I remember right.

 

Thanks, I referred to the idle screw as "hidden" because to most people it is. In my case the throttle body came with it exposed. The issue is that since the screw is not even touching the pivoting lever "backing off" it to adjust the idle downward isn't an option.

How much does timing affect the idle speed? I assume the car is at 0 BTDC and will likely be adding some advance this afternoon. Is that the knd of thing that would give me more power but a lower idle? Doesn't sound right now that I've typed it, but maybe?

Thanks.

Dave

 

Oh ok got it. Sorry man I have no ideas for you

 

I know you said you put a stronger spring on the Throttle linkage.
Are you able to lower the idle by physically closing the throttle plates by hand?

Is there a vacuum leak? Did you use your original IAC, TPS etc...? Maybe the IAC needs reset.

I bought a CFM-Tech TB from a member here on TGO just to check it out. He indicated he had a lot of problems with getting the idle right and to work correctly in general. Once I rec'd it, I could see why- The throttle plates were shifted slightly on the shaft, this would not allow the plates to close the correct amount. If allowed to close too tightly, it is difficult to twist the Throttle Shaft from completely closed to open position- it will tend to "pop" open, affecting drivability. There was also a dingle-berry in one of the idle cicuit ports. I saw it come shooting out when cleaning the unit with compressed air.

I think you said the unit is bored out. Is the idle circuit still usable? The one I had bored by Tom Bishop (eBay) had the idle circuits plugged (on purpose) prior to it being bored- I had to drill them out to re-estabilish the idle circuit. If the idle air cicuit is still usable, it will appear a single small hole in each bore of the Throttle Body- just above each throttle plate- towards the front of the unit.

Have you contacted the manufacturer? I know these units are pricey when purchased directly from CFM- they should have a few pointers also.

S-D

 

Did they install bushings in the tbi? The areas in the casting that the throttle shaft rides on will wear into an off-center egg shape from the force both on the tbi blades and the return spring. This causes the throttle blades to hang on the walls of the bores. Easy way to tell is to open the throttle 1/4 of the way by hand and firmly try to move the throttle shaft up and down.

 

Is that for real??? Can you post a pic of the engine compartment? Id like to have a look at how well the 305 fits.

Actually, on second thought, emailing the pics would be better so I dont hijack your thread. Dimented24x7@aol.com

 

The issue was resolved last night. Thanks to all who responded. Perhaps being able to sit down and write about it cleared the fog or let me have a new look at the situation. It turns out that the idle adjustment screw was functioning properly and after I reset the timing, the idle was adjustable back down to "normal". As for the CFM throttle bodies, I couldn't be happier with the quality of the product and their follow-up to issues. The "pop" that was referred to where the throttle gets buried in the bore and srtticks momentarily is the exact reason I switched out my old popping throttle body. If you have one that pops, it's pretty old. Again, my experience with CFM is very positive. Thanks again.

As to the question of the 300TD, yes it's real...and I will take pictures when it's presentable. It fits "fine" but the engine compartment isn't ready for any pictures yet. One day soon. Thanks for the interest.

Dave