First start after rebuild. Need help with 2 issues
 

I started my rebuilt engine last night, and it started right up and ran well. I let it idle at 2k for about 20 minutes, then drove around my block a couple times and parked it and let it idle more. I ran into two problems.

First, I have a decent oil leak coming from around the turbos. After idling there was a 2" puddle under them, and today I see oil on the subframe and streaks on the turbo heat shields. I can't figure out where the oil leak is though. I started taking stuff out, but I feel like the oil that was on the turbos all burned off, so I am not sure how to track down the leak. There are several streaks across the entire heat shield, which makes me think it's coming from higher up somewhere.

https://cimg0.ibsrv.net/gimg/www.rx7...f447935fa7.jpg


The second issue is the idle. I kept trying to back it down to 1500rpm but it would start sputtering and dipping. By the time I shut to car off, it was doing it up at 2000rpm too. I'm not sure how to begin addressing this, or if it's normal for a fresh engine. The first start instructions I have made it seem like it should be able to idle at 1500 pretty quickly. Here's a video, any help is appreciated


<iframe width="560" height="315" src="https://www.youtube.com/embed/2-1IjfChqhU" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>

On the oil leak, I've had this happen to me when I filled the oil in the car without a funnel, just dumped the oil in the fill neck. Some of the oil went into the PCV hose, which goes to the intake, which can drip down from above to the turbos. That may not be anything big to worry about. I would probably check the turbo oil feed line to make sure it's dry, but besides that you're probably OK.

I can't watch the video right now but it's not uncommon to have idle problems on a fresh motor. Could be a vacuum leak, MAP sensor not hooked up right, plug wires on wrong, etc. - there are a lot of variables. I'll try and watch the video later so I can see and hear what you are experiencing.

Before the rebuild was the motor running well? As in all the stuff bolted to the motor was in good shape?

Dale

Thanks. I may just start the car again and see if there is still that much of a leak, and see if I can spot the source this time now that I know roughly where to look.

The motor ran great before the rebuild. It had good compression and the turbos worked well (correct boost pattern), although the cracks inside the cast iron housings and oil leak on the rear turbo make me think they're at the end of their life. The rear turbo had oil residue but never dripped on my garage floor before. I wouldn't have rebuilt if the thermostat hadn't failed to open, causing me to overheat and lose a coolant seal.

I replaced all my vacuum hoses with good quality silicon, but maybe there is a vacuum leak somewhere. I haven't wanted to start it again yet to find out, on account of the oil leak. Dumb question, but where is the MAP sensor on this car? Is it inside the throttle body? I don't recall seeing it

Firewall, drivers side near the brake booster.

https://www.rx7club.com/attachment.php?postid=1027458

Ah yeah, it's hooked up with new silicon

Do you have a PowerFC or stock ECU?

ISC hooked up?

Dale

Stock ECU. I have a PowerFC, commander, and datalogit in a box which I'll install as soon as this car is running OK. I added a downpipe with the rebuild to replace the precat, and the powerfc is to account for that. If the ISC is also called the idle air control, between the throttle body and firewall, then it's plugged in.

I feel dumb - I just remembered my check engine light came on when I started it. It told me that there was a problem with the intake air sensor (code 11), and it turns out it wasn’t plugged in! I fixed that, so I’m willing to bet my idle problem will be fixed. I’ll find out tomorrow

As a buddy of mine used to say "that may not be the problem but it's sure not helping things".

Keep us posted!

Dale

Alright, I drove around for about an hour today. The oil leak seems to be gone – no idea why. I'll just keep an eye on the oil level and turbos to see if it comes back.

The check engine light is off now that the intake air temp sensor is plugged in, but the idle issue remains. Pretty much anything under 2k and it starts acting up. It does it sometimes when I let off the gas in gear also. I'm not sure what would cause this, so I am not sure how to start troubleshooting it

Years ago I had a similar 'hunting idle' issue (but never the excessively high rpm) that ultimately was "fixed" by adding a couple of extra wiring grounds. I say "fixed" because after adding the grounds the problem went away...but I've not gone and unhooked them to see if the problem returned.

I swapped to a different used set of plugs and double checked that the wires were going to the right plugs, and I'm still having the idle issue.

I did also discover that the idle surges when I push in the clutch. It stops dropping and slowly climbs to around 2500 rpm. I'll start researching what would cause that.

One other question. I've started the car 3 times now and each subsequent time I've had to add a lot of coolant, maybe a pint or so. I hear gurgling when the car is cooling off, and this last time I saw a lot of smoke on startup. I rebuilt the engine due to a blown coolant seal so this really makes me nervous. Is this normal for a rebuild?

I find that it takes about week to completely burp the engine after rebuild.

Try disconnecting the ISC when the engine idle starts hunting. You should notice it will stabilize.
Try adjusting the manual idle screw in or out ... then reconnecting the ISC to see which improves the hunting problem.
Count the turns to full close before the above step as reference.
Barry

I checked everywhere I could reach with carb cleaner, and didn't find a vacuum leak. My vacuum is about 18inHG at 2k rpm anyway, which I think is good? I double checked the grounds that I know of. By the ECM, under the AC compressor, and UIM to firewall.

I realized that this is probably not 'idle dropping' but rather surging/hunting. If I give it some gas while parked in neutral, the same thing happens. I have to apply an actual load on the engine (such as driving) for it to stop.

I have a J&S knock sensor installed by the previous owner, and I had to cut the wire from the sensor to get the engine out. I didn't know if it could cause the ECM to act up, but I reconnected that wire and nothing changed, so I'm still looking.

I unplugged the idle air control valve, started the car, and it immediately started hunting again just the same as before

Any porting done when the engine was rebuilt?

No, the car is stock except for a handful of things. Downpipe, RB catback exhaust, Koyo radiator, and silicon vacuum hoses installed during the rebuild.

The first-start instructions from my engine builder had me adjust the coarse idle screw, the one just to the front of the throttle body pointing up. I turned it about 3 turns in so it would idle over 1500rpm. It's still turned a lot more than it used to be, and from what I am reading that could affect how the TPS reads? If so, should I readjust the TPS and see if that fixes it, or put the screw back to a normal position and hope the new engine doesn't wind up stalling?

Shouldn't need to mess with any TB settings on a rebuild unless there are compression problems. I never have that I can recall on the engines I built. I have done it once to bandaid a problem that turned out to be low compression from poorly resurfaced housings.

Don't adjust TPS to suit temporary TB settings.. that would just make the ECU think you're throttle is closed when it's actually cracked open. You'll have to re-adjust after returning TB to correct setting, which IMO should never need to be fiddled with.

Set throttle body screw back to stock best you can and see what that does for you. If you really want the car to idle up, use the air adjusting screw under the TB/intake elbow.

Also, you might consider hooking up the PFC. It's an INVALUABLE tool for diagnosing bad sensor inputs as you can display sensor voltages on the commander. Compare those voltagees to FSM values. In addition you can use the PFC to change idle speed from the commander... no screw tinkering necessary.

I messed with the coarse idle screw and got interesting results. After I backed it off enough, the engine actually idled perfectly smoothly. With the screw all the way out I got down to 1000rpm. As soon as I gave it gas though without any real load (not driving), I got the same surging. I'm attaching a new video. So the problem still isn't solved, although I guess I made progress


I am worried about installing the powerFC now because the instructions say the car has to be in good running condition to install it, and with this surge issue mine is not. Is it safe to install at this point? Can I install it without starting the car and get valid voltages from the sensors?

You'll be totally fine installing the PFC now. That will also let you check all the sensors to make sure they're reporting in properly.

I would also pull and clean the ISC, if it sticks you can get that surging idle. Also make sure the throttle cable isn't too tight, that will do weird stuff. And check the clutch switch, a bad clutch switch will do a goofy idle on the stock ECU.

Dale

I just realized you wrote the install guide for the PowerFC that I'm using, Dale!

My surge went away after install the PowerFC. The TPS and MAPS voltages are in spec when the engine is warm, but I do now have a slight misfire every couple seconds when I'm not idling. The car wanted to die returning to idle at 900rpm until it got warm, which is annoying but probably due to it being a fresh rebuild. I'll look into ways to prevent that, and I'll pick up a new set of plugs before I jump to conclusions about the misfire.

What is the difference between the PowerFC and stock ECM that would cause the surge to go away with the switch?

The PFC controls idle differently than the stock ECU. Hell, could be the clutch switch (you can check that easily in the sensor check screen) - the stock ECU will do all sorts of weird crap with a bad clutch switch.

The slight misfire is probably due to new engine and break-in. I wouldn't worry too much about that.

The coolant correction maps in the PowerFC aren't great out of the box, when it's closer to 30-40 deg. outside I would have problems with the motor wanting to stall. I imagine where you are the temps are cold. I can't remember if I put that in the FAQ or not, it may be written up somewhere. It's an easy change on the Commander.

Dale

Dude, the PFC and proper use of it solves most running conditions on these engines. If I had it my way, you wouldn't be able to legally register an FD with the stock ECU in the US.

Where you should be worried is altering ignition or anything that affects fuel delivery without doing a ton of research first.

Nice work, sounds like you're back on track.

Alright, I think I've almost fixed all my problems. Tonight I noticed that the neutral switch was not on on my powerFC, even when I was in neutral. Turns out the sensor was loose, and after tightening it the car ran better all around. According to page F-75 of the service manual, the neutral switch, like the clutch switch, has an impact on idle. This explains why I got a surge when I pushed the clutch in on the stock ECM – only when the clutch was pushed in did the ECM think a gear wasn't engaged.

I do still have a little trouble returning to idle on deceleration. I set my non AC idles in the commander to 900rpm, and the corresponding fuel cut rpm to 1200, but when I let off the gas, the rpms drop straight to 1k, then bounce up to 1500, then drop, and repeat this surge a couple times before settling around 1000rpm. So it still has a temporary surge on deceleration and a slightly high idle that I need to figure out - let me know if you have ideas.

The misfire seems to be fainter. I'll still throw new plugs in anyway but it's probably just new engine stuff (it only has 35 miles on it now). I'm happy that my car is drivable just a week after the first start. My GSL-SE took months of tweaking throttle body settings before it idled and ran perfectly, and lots of learning.

Thanks for all the help in this thread!!