Not revving high when cold and minor miss

[rjkoop]

Things are generally good with the car. Just 1 last nagging issue that's difficult to figure out. When I start the car cold it will start but doesn't rev very high. Maybe about 1000rpm and when warm idles about 850rpm. There isn't much difference in the rpm between a cold start and a warm engine. And when it's warm and you restart it idles low for the 1st 30 seconds or so then seems to move back up to about 850rpm. Never have to use the gas to keep it going but struggles a bit. Not sure it's related but when running I sometimes hear what sounds like a minor miss or a muted puffing sound (hard to describe). RPMs sometimes go up and down and only slightly (don't even see the RPM needle move though you can hear a slight change). Driving and acceleration are perfectly fine though. Things I've checked...
- coil - within specs
- distributor - looks fine
- AFM - taken apart, track good, door moves freely
- no air leaks - tested by removing, looking for cracks and using propane when engine running
- AAV - cleaned and I see triangle through opening when cold
- ECU - checked resistence values
- cold start injector - works - engine won't start cold with it unplugged
- coolant T temp sensor - resistance looks correct at various temperatures when measured from ECU connector
- all grounds all cleaned and connected fine - including main ground straps
- plugs and connectors good
- fuel pressure good
- fuel clean
- fuel return (or is it called one-way, can't remember) valve working correctly (was plugged up before but I fixed this)
- replaced O-ring on idle adjustment screw
- adjusted idle correctly

Anything else to look into? Or maybe I should be happy that it generally runs fine...

Here's a few videos. Not great but someone may notice something.

Cold start...
https://youtu.be/6eNUsQJyX0c

Running when cold...
https://youtu.be/-FJuNw7mJfI

Running when warmer...
https://youtu.be/Y6vqjvQav3E

I'm leaning towards a minor air leak but couldn't find one.

Richard

[kilrwail]

Maybe dirty injectors. Buy a can of Sea Foam, put it in the tank and let it run until warm - drive it if possible. Can't hurt and might help.

[rjkoop]

Maybe dirty injectors. Buy a can of Sea Foam, put it in the tank and let it run until warm - drive it if possible. Can't hurt and might help.

Good idea. I used seafoam before when I 1st got the car. Used it in tank but after that a lot of work done. So maybe I'll give that another try. It actually caused a few minor leaks which I fixed but its worth a try.

Richard

[rjkoop]

Another video after Seafoam...

https://youtu.be/iVdgdCxDsk8

Looks like at 1:40 the Seafoam kicked in possibly. Or maybe just a coincidence.

I never had my injectors cleaned when I rebuild head. Maybe I should.. or more Seafoam!

[kilrwail]

Sea Foam is cheaper!