i got a 90 gtu, its stock w/ only a rb daul exhaust system n a rebuilt tranny, but it has a high idle at 1500 - 2000. any idea how to fix?

 

1) Make sure the TPS is adjusted to 1K Ohm at full operating temp, then 2) Short the initial set connector and adjust idle to 750. Adjust screw on top of the throttle body (don't forget to remove the initial set connector short). If the problem still exists, check the tension in the throttle cable. If the problem stilol exists, start looking for vacuum leaks.

 

YOu could also check the throttle plate clearance with a feeler gauge. Specs are in the FSM.

 

My thermowax was bad and wasn't kicking down the fast idle cam.

 

i kind of have the same problem too. I adjust the throttle body a couple times and its still is the same too. There's is no vacuum leak on mine. It will be warm up and then maybe after 30 minute or 20 minute of hwy driving the idle will come down to where it suppose to be at 750. The tps is dead on too. Is there a possible chance that it could be the thermowax that making it idle high or something. After the highway driving it will stay there for the whole day until the next day when i start it cold again and then it would idle high again. It will still idle high if the engine is warm no matter how much i mess around with the idle screw. sorry to high jack the thread.

 

i have the same problem as well, i have to wait for at least 30 minutes on a really hot day or even some times ill have to wait 40 minutes until the idle gos down...

 

what could the problem be? I'm irritated by the rpm not going down. I don't want my clutch to be engaging at that high rpm because i still want my clutch to last me.

 

hope it gets sorted

 

anybody have anymore idea on what the problem could be.

 

Reviving thread from the dead to figure this out for myself as well. If I loosen the throttle cable, it idles fine, but will not start unless a 2nd person is barely pushing on the throttle from under the hood. however, if I tighten the throttle cable enough, it starts fine! but it idles at about 1500 with the idle ALL THE WAY DOWN. thats with a wire going from that one wire test connector to the neg battery terminal. AM I DOING SOMETHING WRONG?

 

if idle fluctuates at all theres a vacumm leak somewhere. all the vacumm lines going to senors, actuators, solenoids, ect. take them off, plug them, and see if the idle steadys out. if it takes that long to warm up id bet theres a clog somewhere preventing the thermowax from getting hot coolant, or the wax has melted and seeped out over time. if you remove the decel dashpot on a n/a you can move the screw the thermowax should push, to see if that is the prob.

 

Look in the FSM; adjust the throttle plate such that its clearance at idle throttle (slack cable) is 0.016" - 0.020". There is also usually a hole in the primary thottle plate, which should not be clogged/covered. Once those are verified, adjust the throttle cable such that it is just slack at idle; you be able to push on the throttle linkage and not get any movement, i.e. it is already resting on the stop. Check the thermowax/fast idle cam and make sure it is completely off the roller when the engine is at temperature. Then adjust the idle per the FSM procedure, with the jumper in the initial set connector, and using the idle adjust screw on the top of the throttle body.

Check the BAC for resistance and proper operation per the FSM procedure.

 

If i adjust the throttle cable to where the throttle doesnt move at all when pushed, it idles at about 3000 rpms. and thats WITH the idle set screw all the way down.

How do I replace the thermowax, or where do I even get one?

 

check AWS resistance and for any leaks. its responsible for the 3k rpm at startup.

 

Sounds like you are adjusting in the wrong direction. Adjust the nuts on the throttle cable until the cable is *slack*, such that the throttle spring is putting the throttle against its idle stop. If you can push it further towards idle and get it to move, i.e. it is not on the stop, the cable is not slack enough, or maybe your spring is busted?

On the stop, with the initial set connector jumpered, and the car at operating temp, you should be able to measure 0.016" clearance between the primary throttle and the bore; and the fast idle cam should be clear of the roller. From there you should be able to adust to 750 rpm with the idle set screw.

Its on the back side of the throttle body, near the left side. You can get a new one from Mazda, or a used one from a recycler. Try ApexAutoParts if you do not have a local source. But before you go replacing the thermowax, make sure it is the problem; there is a procedure for testing it in the FSM. There is a mark on the cam for 77F temp; it should be at that position prior to start & warm up. Once at temp, the cam should be completely off the roller. If it is, the thermowax is not the problem. If it is not, it may be just an adjustment. See the FSM.

A 3000 rpm idle is normal for 17 sec after a cold start, due to the AWS system. See the FSM (look at the S5 manual, better description of this system).

 

Make a test light to set the tps, then every time you adjust the idle stop screw, set the tps using the test lights. Do a search and you'll find how to make your own test lights with about 5.00 worth of parts from radio shack.

What had been done to your car prior to your idle issue?

 

It belonged to somebody else. I purchased it for $750, and I KNEW it was floodedd, so I bought it, changed the plugs, wires, let it dry out, shot some oil in, and it started right up.

But something tells me, when it flooded, this guy thought something else was wrong with it and had a field day trying to figure out "why his car wouldn't start".

He told me it'd just been sitting for about 2 months, but those spark plugs had so much liquified, fresh gas on it. he also said the fuel pump was messed up, and he replaced it. There is no receipt. I'm about to pull out the FSM, and do everything to a T. first things first.....Change the coolant thermo sensor.

 

Is your idle bouncing or is it at a steady 1500 - 2000 rpm? Does pushing the clutch in change the idle at all (stop bouncing, cause bouncing, stall car, etc.)?

Have you checked the compression?

 

or air entrance, maybe on the flow .. some little leak there

 

whats the aws resistance ,cuz my car does go up to 3k then goes down to 1200 rpms lowes,,

 

Depends on the temp; there is a table of resistance vs. temperature in the FSM. See the FAQ section. You can defeat the AWS by either starting in gear with the clutch in, or blipping the throttle once right after start. It should then come down to 1500 rpm (cold start), after which it will drop down to the set idle (should be 750) after fully warmed up, assuming the throttle plate is set properly (o.016" clearance at idle; fast idle cam fully off the roller at temp; idle set to 750 with the idle set screw on top of the throttle body while the initial set coupler is jumpered.

 

going to check that out car has been in my cousin house for a couple weeks once i get some of this car im working on out of here ill bring it back to the house and check that out, hopefully by this weekend,thanks

 

I want to correct a technical error in my previous post; the primary throttle plate clearance of 0.016-0.020" is set not at temp with the fast idle cam off the roller, but rather at 77F, with the 77F mark on the idle cam at the center of the roller.