Sudden change to 2000rpm idle speed
 

Greetings all. I have a stock 94 R2 that I bought with 8k miles on it about 6 years ago. I now have 58k on it. it is completely original with the stock motor turbos etc. I am not a newbie when it comes to the FD and am somewhat educated on the 13B. Now it has never given me any major trouble except for the basic RX-7 problems (Y-pipe couping etc). But recently all of a sudden while driving the idle speed has jumped to app. 2000rpms. Whether it is cold or warmed up doesnt make a difference. Upon startup it instantly revs to 2100rpms then within a second or two it starts to bounce from 1900 to 2100rpms on a very steady rhythm. It does this warm or cold (quite embarassing at the fast food drive-thru window :twitch:). I can blip the throttle and it will then fall to about 1100rpm for a second then go right back up. Additionally I have noticed a substantial increase in the rich gas smell from inside and outside the car. Fuel mileage is affected somewhat also. I have jumped the TEN/GND connections and unplugged the map/boost and the ISC for test purposes with no real notable change. Im hoping that someone here has been through this and can offer a piece of advice (no luck with what I found searching this forum). The only thing I think may be left is the lower intake manifold gasket (I cant see if its the metal or paper one) or a loose vacuum line that I may have overlooked. Any advice from a fellow rotaryhead would be greatly appreciated. Thanks.

PS- I plan to get a quick video clip very soon showing exactly what its doing. I figure that would help paint a clearer picture.

Is this car auto or 5sp?

its an R2 so its a 5 speed manual. I will also add that performance doesnt seem to be too affected (although I havent been getting on it real heavy) but the on/off transitions of the turbos is pretty jerky now. Makes it hard to drive smoothly.

Most likely a vacuum leak, or bad idle air control motor, or something is causing the throttle to hang up. Easiest thing is to start spraying carb cleaner around the engine bay and listen for the rpms to drop. When they do, you are near the leak. The IAC often clogs up and sticks. You can try removing it and cleaning it but you can find a good used one cheap.

Thank you 'rotaryexperimentseven' for the tips. I have unplugged the IAC which caused no change but I am going to remove it and check continuity on it. The FSM says it should have 10.7-12.3 ohms. I'll keep you updated. I have uploaded two videos showing the problem on a cold engine and on a freshly driven warm engine just for reference. BTW, I seem to get slightly different rpm results every so often, but I'm sure that doesn't really matter.


94 RX-7 R2 Idle Problem VIDS

http://www.mediafire.com/?sharekey=0...f6de2f38d93145

UPDATE so far...

As I stated before, unplugging the MAP/Boost sensor electrical connection showed no change in the high rpms, BUT I have found that unplugging the vacuum hose from the sensor DID! It still was a little high and smoked a little too much but it made a dramatic improvement (app. 1000 rpm idle). I thought what appeared to be a black check valve at the sensor was broke (as it flowed both ways), but good ol' Dave Clark informed me I was wrong about it. Seriously, thanks Dave.

I have took off the extension manifold and can't find any loose or damaged hoses. I have checked the most common check valves and they all seem okay. I've checked the IAC and it measured 11.3 ohms, so it's good. Also there is no hung up issues with the throttle parts either. I simply see nothing wrong.

So now I think it could be the MAP/Boost sensor itself is bad (because of the change when hose is unplugged). Does anyone know the test procedure for it? I can't seem to find any resistance figures for checking out this sensor. Any further ideas would be truly appreciated. Thanks.

the idle goes to hell when you unplug the map sensor on every rx7.

Do you have any ECU codes?

Also I suggest you verify that your TPS is adjusted properly. How-to is in the FAQ somewhere. :)

Dave

Agree with catch-22 that unplugging a good MAP sensor should cause idle to drop and car to run rich and roughly. That sensor measures the vacuum or boost in the intake manifold and adjusts the A/F mixture to compensate.

A possibility for the high idle is your Accelerated Warmup System ("AWS") valve located under the UIM. It's the one farther toward the LIM than the IAC valve, and if it leaks, it would have the same effect as having the IAC valve open too far. Its coil resistance should be 9.3 - 11.3 ohms, but even if that is OK, there could be something on its valve seat preventing total closure.

(BTW, I have been chasing a high idle for 3 years, and still have not found the source. Only thing left for me is the LIM-to-engine gasket leaking.)

I haven't noticed any. But funny you mention that, because that's the first thing I'm going to check to be definitve (the extension manifold is still off right now though). I'll have to let you know on that. I so wish I had made a specific effort to check that when it was still assembled (my dad was the one in the drivers seat during those times).

>wstrohm, the thing is it idles at like 1800rpms with the map sensor connected. I had disconnected it (per FSM) to check for change. only until I unplugged the hose from it did the rpms drop. That's the only thing that making me wonder.

I'll definitely check the AWS but isn't that only for cold engine? My issue is constant under any temperature.

So how high is your idle? Three years, that sucks! I can only hope it's not the gasket myself. That's a real PIA as I understand...

I have considered (and researched) that, but the screws holding it are completely tight. The idle problem happened all of a sudden months ago. I guess I figured that if it didn't move then it wouldn't be the problem. But yeah absolutely I should at least check for the proper volts in short/full range. :)

i unpluigged my map/boost sensor and my car stumbled and cut off what could this mean?

1500 rpm with the Air Bypass Screw closed, and both primary and secondary throttle screws backed completely off.

when idling i have idle surge from 3000-3500 rpms when i unplugged the TPS it idled steady at about 3800 rpms... is this abad TPS btw the car was cold

Hi, do you still the smell fuel? If so you might want to fix that first. I have 1993 CAL car and had some what same problem. My idel was high and will not come down. My fuel smell was coming from the primary injector. Found 1 was leaking and replace both. This is a good time to (replace with better brand). If not go stock, they are not cheap. After i replace the fuel leak and smell is gone, my idel was still high but i feel safe because there is no more fuel smell. You might have to do a TPS adjustment. I don't have the link but you can find it on this fourm. I did the adjustmento and now its fine. Idel at 800 rpm when fully warm up. Let me know if you help?

[QUOTE=fongman916;8954918]Hi, do you still the smell fuel?QUOTE]

The fuel smell is still there. It only happened when my idle speed went awry (very suddenly). It's strong enough for me to notice in the cabin, but not over-powering or anything. I haven't had a chance to mess it with these last few days, but I going to re-check for an engine code and check the voltage of the TPS first. I'll definitely update here what I find.

A fuel smell (unburned fuel) is a much more serious problem than a high idle. If the Fuel Pulsation Damper is leaking, or a fuel injector O-ring, or a bad fuel hose, you run the risk of a fire. The FD seems particularly vulnerable to fires due to fuel leaks, from what I have read on this forum. We had a fuel leak on our '94, and it was the FPD.

Fuel leaking will effect your idel too. I would 1st fix that. To check for the leak, you would have to take the Upper intake manifold off. You should be able to see the fuel rail. Turn you key on, engine off and jump the wires on the diagnostic so that the fuel pump will ran. You should see fuel or smell fuel

i did this same test when i was putting my engine bay together, i saw/smelled no leaks with this procedure, but on the first start up i had a strong fuel smell and it made a puddle under my car. then i took the manifold off again and did the same test and again no fuel, so i used pliers and pinched off the fuel return line and then i saw the fuel leak, so it would be a good idea to squeeze off the return line when testing for leaks, it seems to be a better test then just running the fuel pump on high.