Replacement engine stalls at idle?
 

My '04 (totally stock) just had it's engine replaced, along with:

Coils/wires/plugs
Front O2 Sensor
Battery
Battery terminals
Clutch
Belts
Engine Mounts
SSV

I went to pick up the car today, and when I started it (cold) in the lot, it started fine... but the idles surges up to 3,000 rpm, cuts out, catches itself around 1,000 rpm, surges to 3,000 again, cuts out, catches itself around 700 rpm, surges up again, cuts out... stalls. Repeat for every start.

It didn't idle rough, it just wouldn't stabilize... surge, cut, surge, cut, stall.

Obviously I left it with them, and they'll look into it tomorrow. I'm just fishing for suggestions to pass onto him? I searched, but most of the suggestions were to replace things I already replaced, as you see.

Anything obvious the tech may have missed when installing a new engine that would account for it?

Might it be as simple as needing to do the 20-stomp brake pedal thing? Wish I'd thought of that while there...

You are just having all sorts of problems aren't you? lol.

Honestly, I think after everything I've read since joining, that really should be the very first thing an owner does after getting their car back.

BC.

Are there any CEL's? Sounds like the throttle position sensor is acting up. Like the throttle butterfly is stuck. I would look into that.

You took the words out of my mouth, lmao

Does this not happen after the ECU is reset until it re-learns , it does with my 04 .

I wondered, but they drove it for at least 12 miles after the engine was replaced, then replaced the SSV (it stuck when hot), and said it was running fine at that point.

I've pulled the Room Fuse a few times over the years, and yes, it idled a LITTLE erratic (like betweeen 750 and 1000) for a few seconds then settled down.

This is crazy though, it zooms up to high rpm, cuts out, catches itself just before it stalls... zoooms waaaaaay back up, cuts out... repeat a few times when it just dies. It's not slightly erratic, it's possessed.

No CELS when I tried it, no. And it started pretty easily. Just won't stay running. And hey, at least it didn't flood, lol.

They're looking at it now. I guess you guys are as puzzled as I am, and there isn't much to suggest?

I'll mention the throttle thing though, and the eccentric shaft.

Vacuum leak?

Although the amount of swing in your idle numbers is greater than I have seen posted by others here, another guess might be a problem with either the neutral or clutch switches. Here are a couple of good posts to check out to see if this is a suggestion worth pursuing or not:
https://www.rx8club.com/series-i-trouble-shooting-95/neutral-switch-133529/
https://www.rx8club.com/series-i-do-yourself-forum-73/diy-test-neutral-reverse-switch-200453/

Hey, that's very interesting, especially since I had the clutch replaced along with the engine. I've sent these ideas on to the tech. They're gonna hate me playing mechanic lol, but anything I can do to get a working car back asap I'll try.

Well they checked the switches mentioned (amoungst other things) and they seemed OK.

The tech experienced the idle problem too when he started it cold this morning, but they've since run fuel injector cleaner through it and have been driving it around all day... and it's idled perfectly since then.

They also let it sit for two hours, and it still idled OK when started again.

But a similar thing happened yesterday too, as it ran and idled fine all day while they drove it around, so they assumed everything was OK and scheduled my pickup. But after it'd cooled for many hours, it idled erratically for me when I got there.

So whatever the issue is (hopefully WAS), it only happened when the engine was cold, if that's any clue?

To close this issue...

Got my car back tonight (woo hoo!) and it's been idling fine now, even when started cold.

The difference is that they cleaned not only the injectors, but also the throttle body, air intake system and intake valves.

So it'd seem that some or all of those things can fix an erratic idle problem :)