Hello, so my son and I are working on an OG restoration for a 1993 FD while I take a couple weeks off work, and first step is replacing emission parts so we can get a clear smog check in California (it had passed a few years ago under a prior owner). After that we will step into an engine rebuild. Current problem is that car is currently running really high cold idle (3,500 rpm).

So car had heavy modifications when we bought it, including high flow exhaust (downpipe, cat, cat-back), double throttle delete, EGR delete, ISC delete, AWS delete, ACV delete, air pump delete, AEM Wideband UEGO O2 sensor, aftermarket intercooler, aftermarket coils and wires, and a Power FC. O2 sensor is also currently not connected to power FC, and power FC has O2 control and idle control disabled (we'll eventually add a second stock O2 sensor to the Power FC so it can better clean up emissions). Rats nest previously had vacuum hoses replaced and injectors cleaned, and the car still has the twin sequential turbos. Note that a lot of parts around the engine were not bolted back in place and had uninsulated unused wires left exposed so I'm not sure how careful the prior owner had been.

So to retrace our steps we had purchased a used OEM cat and downpipe and installed those with no problem. Car ran fine, although didn't sound as fun.

Then we installed used air pump with new belts, used ACV, used secondary air pipe, and used AWS, and when we started up revs were super high (~4k). We only ran for a few seconds at the high revs cause it was pretty scary.

After that we tried removing AWS, swapping back and forth from power FC to stock computer, installing ISC, uninstalling ISC, and in all cases revs were still high at cold startup (note we didn't think to enable idle control in the Power FC, but we did try the stock computer).

We also tried testing the MAP sensor which was healthy, checking the TPS which gave in spec readings at hot idle and wide open, inspecting the butterflies which sequence correctly and rotate freely, and rotating the high idle cam at startup to try and lower the revs with the hot idle throttle position but none of that made a difference.

Tomorrow I'm getting some more vacuum caps for the upper intake manifold caps as they looked pretty cracked and I disturbed them, and will run a smoke machine through the intake to look for leaks as the upper intake manifold has been on and off a bunch and we might have caused a leak. Other than that we're pretty stumped and looking for ideas. As I see it with the port plates for ISC and AWS back in place there really isn't difference from the prior throttle config which could introduce extra air nto the intake manifold (assuming that's the problem). I also figure the ACV can't have an effect on the intake as it doesn't connect into that part of the system, but I might be wrong? Could a leaky hose even cause such high throttle?

Well any way, would appreciate any advice - we're pretty new to RX7 engine work and have been learning a ton through the manuals and forums. We will hopefully be pushing into an engine tear down next week, but really want the car back in a healthy running state first!

Thanks!
Walter

 

Almost has to be a huge (vacuum) leak into the intake manifold past the throttle body to let in enough air to raise the idle that much. If it's not that, then the throttle plates are being held open by some interference or not enough slack in the throttle cable to allow the butterflies to close.

 

So we had a somewhat successful day today. We found two cracked caps on the manifold that we replaced and that got us a stable idle at 2,500 rpm - high but way less scary than yesterday. Adjusting the throttle position down a bit on the next run gave a surging idle between 2,200 rpm and 2,000 rpm every couple seconds. We watched the exhaust UEGO O2 sensor and manifold pressure - when ramping to 2,200 rpm air/fuel was about 14 and vacuum was ~20 inHg, and when dropping to 2,000 rpm air/fuel was about 20 (lean) and vacuum was 15 inHg. Not sure what to make of that but seems interesting to me (I like data).

When we had the manifold off we also checked the butterflies by shining a flashlight from behind. There was no light getting through at the hot idle throttle setting, and the mechanism moved freely. Note my son hasn't been pushing the throttle when starting, so the butterflies shouldn't have moved and had a chance to get stuck open.

Another finding we had when tracing the rats nest was that we missed running the vacuum line for the ACS solenoids when we installed that system. That means the relief1 and switching solenoids don't have a vacuum feed which would make the system behave weirdly. We won't be getting more Viton check valves for a couple days so can't finish hooking up the vacuum feed for the ACS tomorrow which is a bit sad.

So tomorrow we'll run the smoke test on the manifold to look for other leaks (the tester arrived after we packed up today), and we'll try disabling the rest of the ACS system and air pump to see if that affects idle. Let us know if anyone has any other things we should try - given we won't have the Viton valves to finish the ACS, if we don't find something interesting in the morning we'll probably proceed with the engine rebuild.

 

Put 2 coins between the 'B' adjusting screw so you can knock the high idle cam out of the equation. Tune it after you get the car to idle right; the throttle body is a learning curve on its own. Here is a useful thread to read. Post number 8 is handy too.. https://www.rx7club.com/3rd-generati...ncing-1147118/

 

Read my guide for some info -

https://www.rx7club.com/3rd-generati...ncing-1147118/

Chip away at it, many times it's multiple small leaks.

Dale

 

Thanks Dale and CreepenJeepen for the link to the post. I think I nailed down all the leaks!

The smoke machine showed that the gasket from the manifold extension to the lower manifold was leaking. Looks like someone had abused the gasket at some point. Added a pic below with smoke coming out (looking at the front inside seam of the manifold, you can kind of see some smoke streaming out on the lower right side of the picture), and another with yesterday's two cracked caps and today's damaged gasket. We swapped out the gasket and the car started up at a stable 900 rpm! Woot!

For reference we bought the smoke machine from Amazon for $50 (AutoLine Pro HyperSmoke Automotive Smoke Machine) - worked great and connected easily into the fuel vapor hose into the manifold. Smoke is a bit tricky to source, but shows up well with a flashlight and a dark background. Highly recommended!

We also tried putting the used ISC back into the manifold (after cleaning with part cleaner as mentioned in Dale's thread), but that brought idle back up to 3,000 rpm. We rechecked for leaks with the smoke machine but no new leaks. I figure that ISC must be bad which is unfortunate. Perhaps I could dunk the non-electrical end into an ultrasonic cleaner to see if it can come back to life? If it's a bad seal in there I'm not sure there's any way to pull those things apart and repair, but seems like carbon buildup is the only likely failure mode. Maybe perished rubber?

One other fun note - when the air control valve (ACV) was running without a vacuum source for the relief 1 and switching valves the car was super throaty under the hood - I think with the weird ACV valve config there was a path from the exhaust manifold to the intake through the air pump. Unplugging the three ACV solenoid connectors and the air pump clutch connector stopped that noise before we took the car for a test drive - sounded cool but maybe bad for the engine. Waiting on Dave's sweet check valves before hooking that ACV vacuum line up correctly

Well at any rate, should be easy to get the idle dialed in now, but we'll tackle that after the engine rebuild. Wish me luck! Also if anyone knows how to rebuild an ISC or AWS valve let me know!

 

So, the later JDM ACVs don't even have the relief valve 2, split air bypass valve, and the port air bypass valve, those are the three plugs on your wiring harness. They only utilize the "bigger" valves controlled by vacuum, which are the Relief Valve and the Switching Valve. Also, the housing is built differently, so you can't really just unplug it if you want to do the "updated" version. I have the JDM ACV installed, but there is no data to show if it's working properly compared to the USDM version. Do with this information as you will; a lot of people don't mess with emissions, so this info is limited on the forums. The benefit of "updating" the ACV to the JDM one is that they're still available new. If you take apart your USDM ACV, you'll quickly realize the parts are full of carbon and need a good cleaning. Also, the seals on the two "bigger" valves are probably worn or brittle. Rebuild kits used to be sold for these with new valves, but they're hard to find now. Anyway, it's a big rabbit hole; this topic needs a thread on its own.

I would just use what you got now and see what happens. A lot of tedious jobs with these cars.

 

Great summary of your efforts and it sounds like you are close to having things sorted. Obviously you have studied the threads thoroughly.

I don't recall if you mentioned the idle air screw (in the TB) above.

At one stage, in our efforts, we simply removed the ISC valve and left the port open.

The roar was incredible, really gave an appreciation of the violent internal air flow dynamics.

Having been through a reconstitution of a complete sequential set up, I can appreciate your efforts.

In the end, we were defeated by some unforeseen issues, blew a corner seal, and ripped everything out again to put in a super-simplified Power FC set-up.

The very experienced shop, that did the work, argued that they just could not trust a 30 year old stock ecu.

I am sure you have read about Xavier's work with FC tweak, etc. If you love data, that may be a route you eventually take.

 

After thirty hours of shop time, we finally got it running. Has run beautifully ever since.

 

Sorry, took a minute to reply as my engine is scattered over the driveway atm. Thanks creepenjeepen for the info on the JDM ACV, and I’ll poke around for the rebuild kits - at least the ACV is pretty easy to pull off the car so I can hit that later.

To redbul’s point I haven’t played with the air idle screw yet (like the screw under the main butterfly) but it’s on our list after we get through the engine rebuild. Congrats on getting your engine running smooth! To Dale’s point seems like most idle issues are just leaks past the throttle body which benefit from careful assembly (and a smoke machine). Also once everything is up and running I’m really looking forward to getting a Datalogit and playing with the tuning. I’ll check out Xavier’s work