Hello all,

Before I begin, I am aware of what the accelerated warmup sequence is.

Now, on to the problem:

My friend just bought a '90 GTU with 10k on a rebuilt motor. When he starts it cold, it will rev to 3k, then drop down and fluctuate between 1500 and 1200 rpms until it is 100% warmed up (meaning thermostat gauge is in the middle). If he starts it in gear, it will rev to 2k, then fluctuate between 1000 and 1200 rpms.

As the car warms up, the fluctuations occur at a faster rate. Once the thermostat is warm, a quick blip of the throttle gets the rpms to sit at 800 perfectly, with no fluctuations. No idle problems at all after it is warm.

My idea is that the ECU was confused somehow when the motor was rebuilt, so the accelerated warmup sequence is a bit screwy.

Also, I believe blipping the throttle if cold starting in neutral cancels the accelerated warmup sequence. This method does not work on this car, which leads me to believe that the sequence is screwed.

 

**** like this happens to me to.. i dont know..

 

I have an 89 GTU with about 7500 miles on a rebuilt engine and mine does the same thing. I haven't worried about it 'cause when it warms up it idles very well at 700-800 rpms. I am mre concerned about the engine bucking when it gets below 2000 rpm when I am in first or second gear. I am working on that and will see if it helps the idle surge problem.

 

Well the flucuations are normal for a rotary. I've had my car 6yrs and mine has always done that.

 

really? thats what i though to but about two weeks ago there was a write up about idle problems. i forgot who wrote it though. i think the idle is suppose to be steady. supposedly it fluctuates because of a loose vaccuum tube.

 

Common? Yes. NORMAL? No.
I doubt they ran that way when they were new.

CW

 

It is NOT normal for a rotary. When it starts, it should rev up high, then go to a lower RPM, then idle RPM. Not up and down continuously for 5 minutes.

 

Mine idles perfectly normal after the warm up. During the warm up for the last 6 yrs its has always flucuated. The rpms of the car are controlled by the vacumn during the warm up process so as the car warms up the rpms go down so, the flucuations seemed normal.

 

mine just started doing this a few days ago... ~12K on the rebuild.

i dunno what it could be... also, i think my timing is off

 

After the ~15 second 3k fast idle the ECU limits idle revs to 2K.
If anything (fast idle cam, idle stop, or vac leak) pushes it faster, the ECU gives a short fuel cut.
If it's a vac leak, fix it & the zoom zoom goes away.
If not, adjust the fast idle cam screw back to below 2K an it should fast idle smoothly.

Then after it's warmed up, recheck the TPS setting.

 

Here, This is what stopped mine. OEM Mazda Thermostat, make sure you have the right one, and the cold start system, make sure the resovior is full and the little pump for it works.

 

Awesome. I'll check these both out!