Ok, I can't find my previous thread on this, so I'll make a new one. About 3-4 weeks ago, I posted a thread about an engine swap I did. I put an S4 NA engine into an '82 RX-7. Got the car to run, but the engine has serious idle issues. They are so bad, I won't even consider driving the car untill solved. But anyway, my fuel pump seized up, so I'm waiting on that right now. I just want a few opinions.

When warming up, the car seems fine. Runs at a steady 1700 rpm. Don't know what its supposed to be at since I'm a noob to the 2nd gen engines. But, after you rev the engine up during warmup, the revs will go down to about 1400 rpm then back up to a solid 1700 rpm. Other than this, warmup is fine.

Now, on to idling when warm. This is where it gets weird. The car idles at 1700 rpm. Also, it will slowly surge up to almost 3000 rpm sometimes. When the revs come back down from the surge, it will drop to about 1400, go to 1700 rpm for a sec, then repeat. It sorta sounds to me like the TPS is just garbage. The ECU is just not seeing where the throttle is.

So, any thoughts? Any input is appreciated. Please remember that its going to be about mid next week before I get my fuel pump replaced.

 

Nobody have any ideas?

 

What wiring did you use in your FB? Did you swap everything to S4 FC wiring?

 

Likely a combination of the TPS, and vacuum leaks.

When you start a 2nd gen, it should shoot up to 3000RPM for 15 seconds (thankfully, on many cars, that feature is broken or bypassed) then drop to about 1500. As the engine warms up, the idle should fall to the stock 750. Idle issues as you describe are almost always TPS or vacuum leaks.

 

Ok, Thanks aaron. I adjusted the TPS via the "2 light tool". Seemed to be off by quite a bit. I'll also look into removing all those useless emissions solenoids.

 

The "two light" method is useless (in my opinion). You should adjust to the resistance of the TPS. You want to adjust for 1K, and the engine must be fully warm.

 

Ok, thanks, I'll do that then. At least the 2 light method gives me a rough starting point. Where do I measure the resistance at? At the green check connector or what?

 

If you search for "TPS" adjustment, there should be quite a number of threads. You are measuring at the TPS itself. Actually, inlcude my name in that search, because I've posted the procedure many times.

 

Thanks again. Hopefully I get my fuel pump tomorrow and I can see how it goes.

 

HEY!!! I am having the exact same problem with a 91 nonturbo. Everything you are saying happened with mine. It is running like crap and i cant keep it running. It idles so roughly that it eventualy just dies. If you find the the prob please help me!!

 

In my current situation, it seems like it was indeed a combination of the TPS and a vac leak. Right now I've gotten to the point where I beleive the intake manifold gaskets are cracked somewhere. The way I ended up testing it was setting the TPS so its pressed almost all the way down and unscrewing the idle adjust screw until the thread is showing above the intake manifold. That got the car to stay on and idle on its owm (it has a hunting idle that oscillates between 1500 and 1700 rpm). While it was running I spray throttle body cleaner around the edges of the intake manifold gaskets and listened for the engine speed to change while I'm spraying and it does. Once I stop spraying (maybe 2-5 seconds after stopping) the idle goes back down to its previous hunting pattern. Based on that I'm assuming that there is not a tight seal around the gaskets so I've ordered new gaskets which should arrive on Thursday and I'll see if that fixes the problem.

So... my problem isnt fixed yet but thats where I am. Figure you guys might want to try the same process. You shouldnt have to use throttle body cleaner though. I'd say any non-oil based, flammable liquid should work, so basically just dont use WD40 or anything like that. Some people say that even butane works but I tried that but didnt get a response from the engine.

 

Ok, I got my fuel pump today. I started the car up, the engine shoots up to 2000 rpm and then starts to run on 1 rotor. I think this is because I forgot to put one of the large hoses back on the thing I can't remember the name of. Anyway, its the thing on the intake manifold above the exhaust header. I knocked the front hose off (plugged with a bolt since there is no air pump), and I am assuming this caused a major vacuum leak, causing it to just barely idle on one rotor. Anyway, I'll see what happens when my battery is charged up enough to get the engine unflooded from stalling.

BTW, the two light method seems pretty accurate to me. I checked the resistance, and with the two light method I ended up at 1006 ohms.

 

Well, no change. I got her restarted, and she idles solid, but its at 1500 rpm. When the car was warming up, it would surge between 1000rpm and 1500rpm. But when the car was warmed up fully, it would idle at 1500 rpm solid. I think I have a vacuum leak. It runs on both rotors when your on the gas and above 2000 rpm, but only runs on 1 rotor when at idle, which suggests a vacuum leak. I went through this with my carbed 12A before it died. But anyway, now I can't get the car restarted. I think I might be out of gas though, so I'll just go out and get a can of gas whenever my sis gets home with the good ol buick. But anyway, I'll have to go over all the vacuum lines to try to track down this vacuum leak.

 

If you're idling at 1500 RPM when warm, it's likely your cold start cam. Did you run coolant to the thermowax?

 

Hmmmm, mabey thats my problem. For some reason, I can't get coolant to circulate through the engine. It just spits it back out. But now the car won't start again. I went for a ride around the block and it stalled on me about half way around. Now the f***ing thing won't start again.

I really didn't want to do this, but a carb is sounding real nice right now. From the short ride I did have in it, the car had LOTS of power. Even at 1/4 throttle it felt much more powerful than the 12A.

 

Oh yeah, I forgot to mention the condition of the spark plugs. The rear rotor plugs were BLACK. They couldn't have been any blacker. The front plugs were kinda blackend. More normal looking.

 

I idle at a constant 2100 rpm. This is because my idle air control valve or whatever it's called. (The thing that is connected to the intercooler on the left side) is broken. I took that thing off because it acted like a huge vaccume leak, so my car would constantly die at stop signs. I took the vaccume and ran it directly to the intercooler, so now It just idles high.

 

Non turbo here.

 

Always start simple, make sure the springs on the throttle body are in good order and not sticking. I just had that problem w/ my FC as the car would have a high idle on and off until one day it just stuck @ 3K. The TB springs were worn and lacked tension so I picked up a dual return spring setup from the local speed shop. It came w/ a nice polished bracket and fit perfectly...now the idle is rock solid and the throttle has a stiffer more solid feel. A good $5 fix , though one day I'll get a spare TBw/ good springs to be ported/polished so everything is OEM.

 

Nope, throttle is not sticking. I already checked that.

 

Both the leading and trailing plugs? Black plugs would indicate an ignition misfire, or the rotor running rich...Try swapping front/rear injectors.

 

The high idle can also be inoperative thermowax. That was my problem. I took off the throttle body and backed off the cold idle speed untill the cam didn't change the idle position. This is just temporary untill I can replace the thermowax.

 

Ok, this is going to sound stupid, but what is this thermowax you all talk about? I'm still new to these FI rotaries. Another thing I forgot to mention is that the idle adjust screw on top of the throttle body didn't change ANYTHING at all. I turned it all the way out and all the way back in and it didn't change a thing.

 

The thermowax is a component of the cold start system. It's a small wax thermostat that has a plunger. At cold start, the plunger holds the cold start cam in a position with cracks the throttle slightly. This allows the 1500 RPM warmup idle. As coolant flows through the throttle body, the wax melts, plunger goes down, and cold start cam closes the throttle.

If you do not have a coolant feed to the throttle body, the thermowax never melts.

 

Looking at you TB, you see the coolant tube on the top back pointing toward the firewall? The thermowax is the plunger thingy just below it pointing downward. As it's warmed up by the coolant going through it, it pushes out the plunger, which in turn rotates the fast idle cam. All of this crap is almost impossible to see (let alone adjust) with the TB on the car.

Hope that helps.

you might also want to get an FSM for the model year of your engine. They're available on line.