My recent rebuild is having trouble idling below 1k rpm, It has a couple hours of run time. I know rebuilds have a hard time idling low, so it is recommended that the idle is increased for the first 500-1000 miles.

It's an automatic transmission. I can adjust the idle, and set it at 1.5k rpm, and it will sit and run all day long smoothly and without any throttle manipulation. When the car is put in gear, the engine speed drops below 1k rpm and the car dies, so we're unable to drive it to break it in.

Is there any way to manually adjust the idle speed while in gear, so we can keep the car running? Or am I going to have to let it run every day to get the equivalent of 500 miles of driving (10-12 hrs).

 

The idle should be set with the car in neutral. Does it die as well when in neutral or just drive?

 

Just drive and reverse. It idled once, but the rpm dropped to 750. Will the idle in gear be proportionate to the idle in neutral? I mean, if I raise the neutral idle, should it raise the in gear idle as well?

 

There is more load on the engine when in drive so the neutral idle should be a bit higher than in drive. Setting the idle a bit higher in neutral should bump up the drive rpm. If the brakes are being applied when in drive but not neutral that also could drop the idle some as it does on mine. Make sure the brake booster hoses don't have a vacuum leak as well.

 

No vacuum leaks. Went over everything, and even smoked it yesterday, no vacuum leaks at all.
No dip in engine speed when brakes are applied, and when attempting to put it in reverse, I had the car on flat ground, and did not use the brake. Running a bit low on fuel, so the plan for now is to get more gas in it and try letting it run for a few more hours.

Still open to other input, if there is anything that I should check, please speak up.