Remove Deceleration valves

[Bitsyncmaster]

Since I had my old throttle body with the bad deceleration springs, I decided to test what it would do with the valves sealed shut. I just used a rubber washer under a #10/32 screw and nut to close the openings in each throttle plate.

I've only done testing in the garage but it looks like the only possible change is the RPMs may undershoot just a little (with my micro ECU) when you take your foot off the gas. I think that makes sense since with the valves working it would open them at that time and result in "more throttle". There were a few people that tried this 6 or 7 years ago but I don't remember what problems they had running the stock ECU.

I'm going to road test it and if that works out OK, I can modify my ECU software to fix the undershoot.

[dmc6960]

The primary purpose of the decel valves is emissions related. Though it can have an affect on keeping the engine running with a stock setup if the RPMs drop real fast. When I did this I set the idle bypass and balance screws opened up to just under the threshold of needing the idle motor at all. That theory should be no different with your custom idle ECU. Only difference is that yours can probably react to a fast dropping RPM quicker than OEM.

Hot Engine Idle Air Requirements (no accessories on) - 90% bypass screws, 10% idle motor.

This also has the advantage of leaving a large range of movement available from the idle motor for more loaded situations (engine load that is). AC and alternator (fans) load, torque converter (ATs), and even engaging first gear on a manual without using the gas pedal (assuming your fairly soft on the clutch).

[DMCMW Dave]

Since I had my old throttle body with the bad deceleration springs, I decided to test what it would do with the valves sealed shut. I just used a rubber washer under a #10/32 screw and nut to close the openings in each throttle plate..

I would weld or solder the holes. The last thing you want getting sucked through the engine is a #10/32 screw and nut.

Note that the original spring assembly is soldered in place.

[Bitsyncmaster]

I would weld or solder the holes. The last thing you want getting sucked through the engine is a #10/32 screw and nut.

Note that the original spring assembly is soldered in place.

I used nylon locking nuts. Yes the OEM has a threaded adjustment but they soldered to lock it there.

[DMCMW Dave]

I used nylon locking nuts. Yes the OEM has a threaded adjustment but they soldered to lock it there.

I've seen screws pounded into piston tops. After tearing up an intake valve. Not pretty.

[Bitsyncmaster]

I've seen screws pounded into piston tops. After tearing up an intake valve. Not pretty.

Interesting. I would not think the vacuum could pull a steel screw up from the mixture unit into the intake.

[mluder]

Slightly aside on this topic...

If I understand correctly, when the car decelerates it is normal to see a slight RPM surge as you come to a stop... This is the result of the decelerator springs doing their job to keep the engine from dying as you settle into idle?

I've never driven any other DeLorean but my own so I was curious if my car acted normally in this instance.

Cheers
Steven

[DMCMW Dave]

Interesting. I would not think the vacuum could pull a steel screw up from the mixture unit into the intake.

Lots of air flow there. It only has to get around the W pipe and then it's down hill.