rough idle after flushing coolant.
 

Car: 93 rx7 with 91k miles. rebuilt engine with 1.5k miles on it.

I did a pressure test on the cooling system about 2 weeks ago and found a leak (small crack) on the heater hose near the firewall. (The hose looks like this https://www.mazdatrix.com/product/ho...-eng-to-pipel/.) Today, i replaced the hose and flushed and replaced the coolant. I started the car to burp the cooling system out and the idle is rough now (between 500rpm to 650 rpm). The car feels like it wants to stall but it doesnt. I followed the FSM on how to burp the coolant system but the car still idles rough. Before all of this, the idle was usually around 900 rpm. Any thoughts on what can be causing this or why it is doing this?

lots of white smoke at start up then it's fine. when the car is at operating temp (82 deg C), i get a burst of white smoke then it goes away.

Is the car not overheating when you drive it? Sounds kinda scary like a pinched/failed coolant seal. Usually water might leak in ever so slowly and then get pushed out with air from combustion and fill the coolant with air and force it back into the overflow tank. Start the car and check if bubbles just keep rising after you bled it. White smoke usually means water is being burned. Once it heats up it might seal the issue/push air into the cooling system instead of water entering the engine anymore.

the car never overheated before and water temp is usually in the 85 to 87 deg C range when i drive it. There are no bubbles when i start the car and when it's idling. as it is warming up i see an occasional bubble here and there. when i rev up the engine to 2200 to 2800 rpm like the FSM says, i will see some champagne bubbles but it will stop.

i let the car cool down and now it's hard to start. i will have to rev it and keep the revs up (1k-ish) for about 30 seconds before it stays on it's own.

Have you tried adjusting the idle screw (under the intake elbow)? I don't know why it would have been fine before and acting up now, but coolant temperature determines your idle RPM via the fast idle cam. I've had the opposite issue in the past- coolant was no longer reaching the fast idle cam since air bubbles got into the system, and the cam was staying open even after the engine had warmed up. My idle would sit at around 1300 and refuse to go any lower. Coolant is supposed to gradually melt the wax pellet in the cam and cause your idle to drop from ~1800 RPM down to the ideal speed.

It sounds to me like your engine isn't getting enough air. Try getting it running on its own and then slowly open up the idle screw (counter-clockwise). If you think you still need to burp your cooling system, remove the small hose on the back side of the throttle body and have a rag ready. If no coolant comes out, add more like normal and squeeze your radiator hoses until coolant starts to come out of the hose for the throttle body. Reattach that hose, and now you shouldn't be able to add much more. The last bit of remaining air will make its way out via the overflow tank after a few drives.

Try ignoring it

https://www.rx7club.com/3rd-generati...change-712877/

Yeah it ought to settle out if you burp it good.

I was thinking that too but would it fail in a low idle?

Hopefully you just drive it a few more times and it bleeds out the extra air finally. A lot of people have trouble bleeding the coolant. Although if it's not overheating I guess you did a fairly good job.

it is possible the thermowax was plugged or stuck or something, and someone set the idle up like that. then your flush unplugged/unstuck it and now the idle isn't right...

if you're actually seeing smoke, pressure test it again.

Probably what I'm about to say is not the case, but...

When you flushed, you may have dislodged some corrosion that was the last thing supporting a coolant seal and caused a coolant-seal failure. If that's the case, some coolant may be getting into the combustion chamber and causing the low idle and white smoke. Keep a close track of your coolant level. If it continues to go down, you will need to do a cooling system pressure test to diagnose the root cause.

Hopefully it's not a coolant-seal issue.

I doubt it's a coolant seal issue, especially on a fresh engine.

Did you knock the vacuum line to the MAP sensor off while you were working in that area?

You may just have lightly fouled plugs, especially if you backed it out of the garage to do the work then started it after a cold shut down.

May just need a good drive and see how it does.

Dale

i already did a pressure test yesterday after i put everything back together. it held steady at 18 psi for over an hour.

So I looked up the symptoms of a bad or missing map sensor and that does sounds a lot like what my car is doing. Did do a lot of pulling and jerking that hose around to get it off. I'm about to go check it out.

so i feel very stupid. The map sensor was knocked off like Dale said. I remembered see the the line disconnected awhile i was under the car yesterday and i though it was for something else. Since I had the car running 3 separate times for about 30 min each to remove the air from the system, should i change the spark plugs and oil before i go on a drive? I was planning to change both before i tune my car after all this COVID19 stuff calms down.

haha nice! Dale to the rescue, I'd hold off on it until right before you go get it tuned just so you know they're minty fresh. I don't imagine a little drive would hurt it. Also depends on how long the oil has been sitting/how hard you push it. Over a year and change, I'd replace the oil. I say keep the plugs in unless you still have an issue. That way your going into the tune with the freshest plugs possible.

Yay! Glad that was it!

I don't think you have to change oil/plugs because of that. You can just drive the car as usual.

Dale

yesterday after reconnecting thr map sensor the car started fine. I just turned it off and went back in the house. today the car won't start. I was about to take it for a nice drive in the cool weather?

fouled plugs?

Oh man lol, maybe could try and deflood or cranking without EGI in and flush a little fuel out and try again. Engine was probably too cold when you turned it off and the plugs got dowsed and couldn't burn off the fuel from their tips.
I think I read on here somewhere if you got a stock ECU cranking with pedal pushed to the floor puts the car into an auto deflood mode and doesn't fire injectors.

i gotta love being a newb and messing up my car every time i try to fix it. I tried deflooding it. cranking 5x15 seconds when the egi fuse is removed. didnt work. Pulled out the 2 spark plugs i can reach from above the car and they were completely black.

buying new spark plugs and it will be round 2 tomorrow.

thanks for the help.

Bruuutal, should be good after a quick replacement! We all started somewhere! one day you'll be able to figure this kinda stuff out fast.
You figured out the flooding issue fairly quick too. Hope she starts up again with no problems.

Your plugs may have been overdue for replacement. Old or fouled plugs can contribute to flooding problems.

Plugs last maybe 10,000 miles before they start showing signs of age. RX-7's chew through plugs pretty quickly.

In the future, if you need to start the car cold and move the car, you may want to let the car idle for a few minutes then bring the RPM's up to 3000 RPM and turn off the key. That can help a lot. Many times, though, if I need to work on the car in the driveway I'll just push the car where it needs to go.

Dale

Spark plug life depends on the usage, if you're just going down the freeway at 47mph like everyone does here, than you can go 30,000 miles on a set of plugs, however most of us don't, and we should be changing the plugs more often.

https://www.rx7club.com/single-turbo.../#post11743171

"I've visibly witnessed this phenomenon while test firing plugs in a pressure chamber. When BUR9's are brand new they seem ok; however, in very short order they start to wear at the firing end and the spark likes to move way down inside the plug which seems to shroud it from the chamber."

"The hypothesis that I advance is that as the spark moves down inside the plug and/or onto the nose insulator's surface, it becomes effectively more shrouded, cooler and delays flame front travel into the chamber which, for all intents and purposes, "retards" the timing and may slow the overall burn rate as well. This offers one possible explanation for poor or inconsistent power--and that which occurs without an apparent misfire (may also produce high egts too). "

The big thing to remember is this isn't your daily driver Toyota, you won't get 100,000 miles on a set of plugs. The center electrode does wear down over time, it starts as a sharp cylinder then wears down into a rounded nub. The farther it's worn the bigger the plug gap and the weaker the spark.

Rotaries need a LOT of spark energy due to the long combustion chamber, that's also why there are 2 plugs per rotor.

How long they last really depends on how much power you're making, how hard the car is driven, etc.

Dale