Bad idle after rebuild
 

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Got everything assembled. Figured wouldn't start bc I am new. It pushed started but wouldn't idle and no codes. Drove fine so long as I didnt let it drop below 2000rpms. It felt like vaccum leak to me so I started searching. Found a nipple broken that connected to the purge valve super glued and tried again. Still would crank no start. Push started and still no idle. I tested compression with a piston(ikr not accurate but getting desperate after 3 days of trouble shooting ) 80 psi on front and 30 on rear! Feeling desperate again and not wanting to start over but i am starting to accept that I did a shitty job. I put atf in the low comp housing, about 50cc. Still would crank no start but sounded faster.

The whole time it feels like afr is off. Let it be known that I am at 6,800' above sea level. I checked the ultra gauge and it says afr is .9 to 1.0.......I really hope it means 9 to 10. Its actually the same as it was before the rebuild. Well looking into how it calculates ltft and stft I started messing with those sensors. This is where I came to the baro sensor.

I disconnected the baro and I got it to crank and START ! It still idles like shit and is spitting out a ton of white smoke (hope that's the atf bc didnt get that before). Finally idling. Checked oil for coolant and spark plugs, didnt find any but about 15 min of idling started to climb to 230 °f. Turned it off.

I plugged the baro back in while idling and the rpms bounced around and even stabilized a bit but returned to shit eventually.

I suspect that a seal in the rear rotor was binding or stuck. Maybe the atf loosend it up? Or maybe I built a shitty engine, not ruling that out yet and prepared to give it another go. But first, Gonna recheck the comp on the rear tomorrow. Then on the baro gonna test continuity, resistance and wave pattern on the baro bc that bugger is not cheap.

I suspect that the baro may be bad I found an engine control diagnostic that should get me started troubleshooting. It seems that the sensor controls a lot of things including thermostat which may explain it running hot ?

Before removing th baro I did the following:

I have verified spark with test light(bhr coils, wires and new plugs)

Checked fuel pressure in engine bay before injectors ~60 psi

Cleaned maf sensor with electrolytic cleaner.

Reset computer and pulled room fuse.

Cleaned ess.

Gutted cat. ( I removed and cleaned o2 sensors too)


Any suggestions?

This is exactly why I always recommend an engine swap. If you are getting horrible compression in the rear rotor, something is very wrong and ATF isnt gonna solve it. If anything, it can make things worse by damaging your engine coolant seals.

Did you inspect your housings and rotors before putting the engine back together? What did you replace in the engine? Which rebuild kit did you use? It's possible your rear rotor had bad housing or rotor itself. It's impossible to exactly pinpoint what it could be without removing the engine again and cracking it open. Theres definitely a serious problem if you are only seeing 30 PSI in your rear rotor.

.9 to 1 sounds like it's showing you lambda. 1.0 lambda = 14.7 AFR, right on the money.

Also given that it barely runs, I wouldn't put too much stock in the fuel trims it has learned. What is the MAF airflow rate on a warm 800 rpm idle?

See if compression has improved now that you have run it a bit.

I recieved rebuild kit when I purchased car. All inclusive deal. I didnt choose the stuff but it seemed reasonable at the time. It is the Atkins kit and it included new housings too. I understand that their seals are not the greatest. I did corners, sides, apex, oil, and water.

I understand it's easier to swap but I didn't buy a rotary to swap. I want to learn. If it costs me more time and money to do it again. I am not disappointed, It was expected.

It sounds good in theory but here's the mistake you made. You buy the kit only after you crack the engine open so you know what you need. Did you reuse any components? Bearings, seals, springs or otherwise that maybe shouldnt have been reused? Did you clean all the old parts before reinstalling?Sounds like all the problems are on that one rotor if everything you have tried so far has failed. What are your full compression numbers? That will give you a better clue where the problem is. Is it 30 psi across all three rotor faces?

I just tested comp now. Rear one is now 70 psi.

Not sure how I measure across each face ?

Well, ideally you want to use a rotary specific compression tester but you can use a normal one it's a bit more complicated. Check the link below on how to do it. You want to make sure you are hot testing the engine. Cold numbers dont mean anything.

Ok and thank you very much.

It did start right up this morning and the cold idle was great. Before it got to 80° f the idle dropped from 1200 to 800 and it died right away.

At what rpm? Compression on a rotary varies with engine speed, so 70 psi at 200rpm is far better than 70 psi at 300rpm.

It was with engine off so starter speed and it's the upgraded starter.
70psi at 200rpms

That's quite concerning. Look forward to your results.

Definitely with engine off ;)
The upgraded starter, attached to a good battery turns around 300rpm. Age, battery charge level, poor battery connection, etc can all reduce the starting speed. Best to measure it.

Battery is an Optima and I keep a float charger on it.
Good advice and thanks !

My guage doesn't have a Schrader valve..well it does, its built into a button. Attempting to rig something up.
Suppose I gonna have to push start it to get engine warm.

It died before it held 800rpms. But around 1200 it was 7-9

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Cant get my comp test to read all 3 faces. Going to take to Mazda and have them test if I cant get it good by next weekend.

It's been idling and running cool for 25 min now. Its racing up to just under 2k and drops to 800. When it drops to 800 it is rough. The ltft is constantly increasing. Started at 12 and now 17. I think it might be learning ?
Baro sensor is hooked up. Tested fine I just cleaned it.

Just borrow or buy a regular tester they are super cheap. All you want to do is confirm your engine is not broken and that compression is close to passing. If it is, then pay to have it tested by Mazda. Save yourself a few bucks in case your engine is the problem.

I have the harbor freight one. I just tested it hot and it looks bad . Around 60. That's also after driving it. For 20 min. Then it wont start hot.

Looks like I gonna have to pull the engine again...

Where do you suggest I buy the internals from this time?

And of course i will tear down first before i make any purchases.

You'll have to tear it apart again then if you can send pics of all the parts you are using. Any parts you reused the first time should be ordered. You should pretty much see what needs to be replaced. Parts are pretty easy to source, I would reuse the brand new parts you put in for sure. That sucks man sorry, rebuilds can be really tricky to get right. The saving grace is at least now you know exactly where the problems are and what to look for.

No need to feel sorry I really enjoyed the tear down and assembly. If any thing you need to say your welcome. You have helped me a ton and I really appreciate it.

I gotta take a break. Been obsessed for last 3 weeks.
I might tinker with this a bit but probably next weekend I will pull it again. I bet i can do it in half the time this go around.

The right attitude to have about it. I'm sure it will be a beast this time and crush that test.

Just thru me a p0506.

Actual rpm at rough idle is 700 ?

Wondering if I have a vac leak ?

Could be an intake vacuum line, could also be the throttle body itself. Is your air filter also clean? You could also try taking off the intake accordion tube and seeing how the throttle body condition is.

Yeah I just researching all of that. I also noticed that internal engine failure is also a possibility.

I get on it tomorrow and update. Thanks!

Where are you located?

You'd need a real compression tester to be sure, but the wide variance between rotors on a piston tester is not confidence inspiring.You can try manually rotating the rotors with the spark plugs out and see if you can actuate the apex seals by hand to eliminate their being stuck in the rotors. It is possible a corner seal fell out or any number of possibilities, if compression is the source concern.

Most common post-rebuild no start/hard start/rough idle with the RX-8 relate to the fuel injector connections being swapped around. It can mirror weak compression in the sense that it cleans up as RPM increases and the other injector sets are engaged (secondary ports open), though that happens higher in the RPM band than you indicate the engine will remain operational.

This doesn't provide RPM windows, but the second injector set comes online with the secondary intake ports, fueling the two primary ports in addition to the secondary ports. The tertiary ports do not have injectors and are 'air only'.
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