92 MX-3 GS 1.8L - engine revs up and down

[zerialz]

I just got a 92 mx-3 GS.
Not to familiar with the K8s but here goes:

After the car reaches operating temp the car constantly revs between 900 RPM and about 1400 RPM back and forth.

When I bought the car, upon further inspection what appears to be the IAC was unplugged. I plugged it back in and there was no change.

I just did the GND STI(TEN) to put the car into diagnostic and the fans did not come on that should eliminate the cause as being the TPS, right?

If I unplug the TPS the check engine light illuminates but the cars idle stops revving and stays at about 1800 RPM

In diagnostic mode the CEL flashed but I did not count the flashes. The check engine light is not on while driving so I assume it's either flashing the PASS code or stored TPS code from my other diagnostics.

I checked the coolant and it appears to be full with no evidence that I'm losing coolant.

What else should I check?

[zerialz]

A guy from here is going to send me a complete throttle body so I'll update this thread if it resolves my issues. Also while my throttle body is off I plan on replacing as many of the vac lines as I can get to and thoroughly examining the intake tube for splits or cracks.

[mitmaks]

Most likely vacuum leak.

[Daninski]

In diagnostic mode the CEL flashed but I did not count the flashes. The check engine light is not on while driving so I assume it's either flashing the PASS code or stored TPS code from my other diagnostics. What else should I check?

Count the flashes and tell us what codes your throwing then maybe we can help you.

[zerialz]

The codes it threw were isc 34 and tps 12.. to be expected as I unhooked the tps during troubleshooting and the iac was unhooked when i bought the car.. the iac did not throw a light though.. the tps did.. new update: When I unplug the iac and push my AC button the idle stops surging and settles around 1500 RPM I do not have any AC components(compresser, lines, condenser etc.) so it must be some computer parameter like how it idles up for ac clutch engagement and power steering .. at this point I'm fairly confident a complete TB and TB gasket will fix the idle issue.. the TB will ship tomorrow and gasket should arrive tues.. 1 question.. on some diagrams I show you need 2 TB gaskets on the k8 throttle body. Do you? and I do not mean the IAC to throttle body gasket.. it appear as 2 throttle body to intake gaskets.

[windofire]

that really sounds like when my ignitor broke, so my best bet is your ignitor.

what happened to me was that it started to stumple/revs flying all over the place, when it got warm. but if i let it sit, it would drive perfectly after 10-15 mins.

I think that your codes only came because of your isc plug wasn't connected.

[zerialz]

I plugged the iac in with the car running and it starts surging.. unhook it and it stops but only with that ac button on. weird.. I'm not low on coolant so I think the iac is bad..

[windofire]

Okay i see, it isn't the ignitor then.
Check the manual to see if there's a way to test your isc

[[LVPA]93GsSe]

Try checking the connector for the IAC and make sure it isn't checked and broken. This just happened to me and took me a while to find.

[Daninski]

In the old days we all knew what the cause of these issues,,,,Mr EGR He is evil and upsets even the most finely tuned MX-3.
Anyway double check for vacuum leaks then set the TPS, if you haven't done that then that should be step one. setting the TPS should take about 20mins to 1/2 and hour. Take your time it's a very important step.

TPS Adjust
Connect ohmeter to 2 bottom pins (BR and BK/DB) and you should get continuity. If not, loosen 2 TPS retaining bolts and rotate until continuity has just barely been achieved. Semi tighten 2 TPS bolts.
Insert .006" (0.15mm) feeler gauge between the throttle stop screw and throttle lever. This should not break the continuity. If it does break continuity, slightly adjust TPS rotation again to regain the continuity. Insert the gauge in and out a few times to verify.
After confirming continuity with 0.15mm feeler gauge, insert a .020" (.50mm) feeler gauge. This should just barely break continuity. If not re-adjust TPS rotation again. Re-confirm by re-inserting feeler gauge.
In essence, continuity on initial connection to TPS.
Continuity with .15mm gauge inserted.
No continuity with .50mm gauge inserted.
Tighten down TPS retaining bolts.
Re-connect TPS connector.

Once you've adjusted the idle and or TPS let the car run for at least 15 minutes so the ECU can learn the new settings.

Idle Setting
Before adjusting remove the screw and ensure its clean and not damaged.
The screw on the top of the throttle body is what your looking for. Start by adjusting it about 3 turns out then start the engine. With the engine warmed up turn it in till the engine starts to die then gradually turn the screw out untill you read 650 RPM in Diag mode (Ten and Grd jumped). If you turn it too far out your engine will be less responsive so if it feels sluggish afterwards readjust the screw.

[zerialz]

In the old days we all knew what the cause of these issues,,,,Mr EGR He is evil and upsets even the most finely tuned MX-3.
Anyway double check for vacuum leaks then set the TPS, if you haven't done that then that should be step one. setting the TPS should take about 20mins to 1/2 and hour. Take your time it's a very important step.

TPS Adjust
Connect ohmeter to 2 bottom pins (BR and BK/DB) and you should get continuity. If not, loosen 2 TPS retaining bolts and rotate until continuity has just barely been achieved. Semi tighten 2 TPS bolts.
Insert .006" (0.15mm) feeler gauge between the throttle stop screw and throttle lever. This should not break the continuity. If it does break continuity, slightly adjust TPS rotation again to regain the continuity. Insert the gauge in and out a few times to verify.
After confirming continuity with 0.15mm feeler gauge, insert a .020" (.50mm) feeler gauge. This should just barely break continuity. If not re-adjust TPS rotation again. Re-confirm by re-inserting feeler gauge.
In essence, continuity on initial connection to TPS.
Continuity with .15mm gauge inserted.
No continuity with .50mm gauge inserted.
Tighten down TPS retaining bolts.
Re-connect TPS connector.

Once you've adjusted the idle and or TPS let the car run for at least 15 minutes so the ECU can learn the new settings.

Idle Setting
Before adjusting remove the screw and ensure its clean and not damaged.
The screw on the top of the throttle body is what your looking for. Start by adjusting it about 3 turns out then start the engine. With the engine warmed up turn it in till the engine starts to die then gradually turn the screw out untill you read 650 RPM in Diag mode (Ten and Grd jumped). If you turn it too far out your engine will be less responsive so if it feels sluggish afterwards readjust the screw.

Sounds like the complete throttle body and tb gasket will take care of this.. I'll let you all know..

[Daninski]

Sounds like the complete throttle body and tb gasket will take care of this.. I'll let you all know..

You'll still need to set your TPS and Idle. Anyway, if your not interested that's fine just understand that all the rebuilding in the world won't help if the TPS is out of adjustment. Good luck.

[zerialz]

Sounds like the complete throttle body and tb gasket will take care of this.. I'll let you all know..

You'll still need to set your TPS and Idle. Anyway, if your not interested that's fine just understand that all the rebuilding in the world won't help if the TPS is out of adjustment. Good luck.

Trust me.. I fully understand and will not ignore your advice. It's good advice.. I'll use the information you gave to ensure the TPS is in spec and set the base idle with the screw.. Thanks for your help man.

[SuperK]

You will want to make sure the throttle stop screw is still set to factory and hasn't been removed or modified.
Once you verify that the stop screw is in position and hasn't been tampered with, then adjust your TPS. You will want to adjust this no matter what throttle body you have.
Once the TPS is adjusted, then adjust your distributor timing to it's proper location.

If the idle RPM isn't where it should be, then you can fine tune with the idle air adjustment.

If the throttle stop screw HAS been tampered with, then you will need to modify the position of the idle stop screw, THEN readjust the TPS, then timing, then the idle air screw until you're still on the right timing and idle configuration.

remember, every time the idle stop screw is adjusted (heaven forbid it's been tampered with) then the TPS has to be readjusted with a multimeter and feeler gauge.

[zerialz]

I got the throttle body a couple of days ago and the intake gasket set yesterday. Day off is tomorrow so I'll be swapping everything over and setting the idle according to the info given here. Also change the oil and The OPS. About a month from now I have about 12 days vacation so I plan on doing upper gaskets(Everything above the head, VCs, IM, etc.)

Also I need to re-add all the AC components to this car looks like the PO wanted to reduce weight and deleted all of the components. So if any of you had the same goals and have the components laying around that would be great as I'd be interested in purchasing them. No AC in Vegas is not exactly fun.