My RX7 idled just fine until I went in for a clutch job and halfway through decided to check the condition of the turbo. Half the damned engine was torn apart before I got that thing out. (By the way, it's just fine.) Well, the car's back together now, but it's not idling right. It'll start out at 3K RPMs for cold idle, then drop down to 1500 or so, then try to drop lower, but it'll sputter, stall, and die instead.

So, what did I screw up? Where's the vacuum line or missing gasket that's causing this issue? Could definitely use some expert advice!

 

Sounds like possibly a vaccum leak. Did you remove the any of the intake manifold?

Make sure if you removed the MAF that it is plugged back in, but I doubt it would start if not.

Also double check that you hooked up the neutral switch on the transmission, it's located near the shifter.

Oops sorry you asked for expert advice. I'm not an expert.

 

I did not remove the intake manifold, but I did remove just about everything that connects to it. I replaced several cracked vacuum lines with 7/32 hose (I think). I suppose it's possible that one of them is leaking. Is there anything I can do with the car at my house to test for leaks?

The MAF was reconnected.

All of the electronics on the transmission were reconnected with one exception. There's a thin single-wire connection which goes into the harness. I can only assume that it's a ground, because on the end of the wire is a thin black box with a metal stub sticking out that a bolt is put through. I couldn't find any bolts near enough to use.

And as for the expert comment? I've seen professional mechanics scratch their heads and give up, then my friend's father comes in, and has it running in under 5 minutes. I'd like expert advice, but I'm more than willing to try anything

 

Check your neutral switch for continuity in neutral, and none in any gear. Does pushing your clutch to the floor or letting off of it while in neutral make any difference in idle (bouncing vs non bouncing)?

What model 7 is yours? Figure out if that is a ground wire and find or make a place to ground it. I do not think I have a ground wire coming out of that harness down there, not on the transmission harness. One wire goes to the oil pressure sensor, then on down the line I have starter wires, the reverse/5th switch wires and neutral switch.

If you can keep your car running (giving gas or otherwise), then you can take a propane torch turn it on but NOT light it, and blow the gas around everywhere you could possibly have a vac leak. If you get a jump in idle you'll know you found it. Can be done with starter fluid, but it doesn't seem very friendly toward hoses, wires, and being liquid it's more likely to catch fire when it comes in contact with the exhaust, etc.

 

Look at the link below, 1st post second pic and look at the item labeled "C." Is this the item you speak of? It needs to be connected to a proper grounding place such as your slave cylinder which is where it comes connected from the factory but as long as it's grounded properly it doesn't have to be connected to the original spot.

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/starter-wiring-question-pictures-included-907304/

 

The 3000 rpm after a cold start is normal for the first 17 secs. if you don't want it to do that, start in gear (clutch in) and it will defeat the AWS system, or give it a blip on the throttle after start and it will stop the 3000 rpm warm up sequence. The 1500 rpm idle after cold start (afte 17 secs) is normal operation of the fast idle system. After warm up, it should drop down to 750, assuming all is stock and properly adjusted.

If it will not idle after warm up, there are several possibilities:
Vacuum leak
BAC valve not hooked up/not operating
Bypass hole in primary thottle plate clogged
Idle speed setting too low
Idle mixture set to lean or too rich
TPS adjustment

Given the history, i would bet it is a vacuum leak...

 

I wondered if that might be what he was talking about but he said it goes to the harness? That one simply goes from the slave cylinder to the firewall. Mine does at least.

 

That is indeed the one I'm looking at. It goes from the slave cylinder to a connector, then from the connector to the engine harness (or at least a harness under the hood). I'm glad you guys told me where to put it - I was just going to leave it where it was.

So, back on the idling issue: I pretty much drenched the engine bay with carb cleaner attempting to track down the leak while a friend held his foot on the gas to keep the car running. There was no engine response whatsoever. If I've got a leak, it's hidden pretty well.

That leaves the following options:

BAC valve not hooked up/not operating (How do I check?)
Bypass hole in primary thottle plate clogged (Could someone show me a picture?)
Idle speed setting too low (The cables are very slack. I assume this is how you set the idle?)
Idle mixture set to lean or too rich (How do I check and/or adjust?)
TPS adjustment (Elaboration, please?)

 

 

BAC - it's probably fine, unplug it and see if anything changes

Bypass hole - look up ^

Idle speed setting - there is a screw on the back of the UIM that is the stop/idle adjustment it's about an inch or so in front (toward front bumper) of where your throttle cable adjusts.

Idle mixture - factory ecu controls it and adjusts according to airflow, tps, etc.

TPS adjustment - See pictures below. (click thumbnails to enlarge)

Go to Radio Shack and get 2-12volt dc lights (led pictured, but other should work fine as well)

Connect the wires as pictured with spade terminals 3/16" I think(pos/neg doesn't matter, they will light either way)



Take about a 12" piece of wire and attach another spade terminal to one end, and strip the other as shown



================================================== ====
Next get the car up to operating temperature then do the following......


Hook the lights to this green harness as shown (dual wire should be in the odd slot, single wires in the two parallel slots)





Hook the 12" wire to this terminal and to the NEG on the battery post as shown

 

Turn your key to the ON position.

Only one light should be lit up like this.



If neither or both are illuminated, then turn the screw behind the alternator (need to remove the intercooler if Turbo) until only one light illuminates. If you turn it counter clockwise until both light up, then turn it clockwise until one goes out then +1/8 turn. You should be set.

I tried to get a picture of the screw, but without removing the intercooler it's about impossible.
I just grabbed some more batteries I'll go try to get a picture of that adjustment screw for you.


(here you go here is the screw on an s5 TII) the picture distorts how far back that screw is, it is a good way back in there, not near the alt + connector like it looks in the picture.

 

.....

 

One last thought..........

I wouldn't touch the tps adjustment other than maybe to see if one light lit up or not. If it hasn't been tampered with, odds are it's not the problem unless it's going out.

What's the odds that the tps or anything else failed at the exact same time the clutch did? I would go back to the sensors, switches, and the wiring on the transmission, before tinkering with everything else.

I would even check the compression before I started "adjusting" things. The same thing that wore out your clutch could have worn out seals, etc.

 

Thanks Satch for the clarifications.

I've got an S5 and have not tooled on an S4 model, so I was unaware of that difference.

If you still have A/C you should probably use a BAC. <--- Based on what I've read, and I kept mine.

(Satch he doesn't say his is not connected, that was a suggestion of a possible problem)

 

Idle is set with the idle adjust screw, on top of the throttle body where it joins the plenum. It controls the amount of air allowed to bypass the closed throttle through a small passage.

The throttle cable should be adjusted so that is it just barely slack when the primary throttle plate is fully closed, i.e. with your foot off the gas, you should be able to push on the primary thottle linkage and get no movement because it is on the stop. Any more slack than this is not a good thing, as it makes for a 'dead spot' in the initial throttle response.

you can check the BAC by pulling the electrical connector off; if there is no change in the idle, its not working. You can check the BAC for resistance (spec in FSM), and sound (should click when 12v applied).

Dunnno about the S5, but in my S4 there is a *second* intake air temp sensor, mounted in the plenum chamber, which is there to adjust the BAC signal for changes in its resistance over temperature.

 

The ground that TeeJayHoward left off the one labeled as 'C' in the first picture on https://www.rx7club.com/showthread.php?t=907304

What part of the wiring harness does it come out of? For I don't know how long.