RPM up and down

Need a little help from the experts here
After the car is up in temperature the idle speed goes up an down when stopping at a light 1300 then next stop 1300 and so on
Is there a regulator that controls this,where should I start
1988 328gts

 

First off check the carpet, the cable can get caught. Then assuming injection engine you will see a spring loaded bracket on top of the engine , this is the cable from your feet to the engine, see if this is sticking and give a squirt of wd 40 , work it by hand so it snaps shut against the stop. If not that then plenty more it could be.

 

Could be a bad 02 sensor and it’s cycling but could be any other things too.

 

I checked all that also did the lube just to make it clear the RPM changes up and down without touching the gas pedal

 

There are no Cat on the Car just a true pipe with the sensor in it

 

Ok so it does still have the 02 sensor hooked up, try unplugging the wire and see if the idle still Fluctuate up and down.

 

Probably not even relevant here but there is a small hose located under the coolant expansion tank on my old QV that worked its way off and caused RPM to swing from 800 - 1200 RPM. Just needed to pushed back in place and problem solved. Hoped the fix is as easy for you

 

This has to wait till the Car is on a lift

 

Ok but I think you can access the plug from the o2 sensor from the top or the rear right wheel well.

 

Are you saying that sometimes when you come to a stop the idle is OK at 1000 RPM (and steady) and then other times when you come to a stop the idle is 1300 RPM (and steady)? Or please restate the trouble as you wrote "1300 then...1300..." (like it never is changing).

If so, you should verify the operation of the throttle idle microswitch. At idle, it should be closed, and this "tells" the Microplex ignition ECU to retard the timing a few degrees which reduces the idle speed and is the condition where the Mechanic set the 1000 RPM warm idle. If it doesn't close at idle (as it should, the idle speed will be increased). One easy way to test this is to just unplug it when at warm idle. If the idle speed increases = it's working correctly. If the idle speed doesn't increase when you unplug it = it's not working -- i.e., if at 1300 RPM idle speed, and you unplug the throttle microswitch and nothing happens = it's not working (and could just be mis-adjusted or bad):

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Is that the switch at the quadrant on top of the engine where the accelerator cable connects ??

 

Also, verify the RPM's drop rapidly when releasing the pedal.

 

Thank you Steve just to make it clear when I stop with a hot engine the RPMs can be at a 1000 or1300 or 1300 and go down to 1000 al by itself just sitting at a red light

 

Yes sometimes when I olio the pedal is goes down to 1000 RPM but it also goes back up by itself just sitting there

 

It mounts on the other end of the throttle shaft -- item 48 here (for a 328):

https://www.ferrariparts.co.uk/diagram/ferrari/328-gtb-gts-(1988)/017-throttle-housing-and-linkage

 

I recall it from my 3.2 mondial but gone 7 years ago. Owned for 20 years, pt ex and used prices went through the roof 12 months later.

 

Yes, that would be a strong symptom that the idle throttle microswitch is the trouble (either being misadjusted or having a slightly changing/random high resistance at the idle contacts when closed that is sometimes low enough for the injection ECU to think that it is closed and other times high enough to think that it is open), and should be the first thing to rule in or out. As I said, when it is (wrongly) at the 1300 RPM warm idle, just unplug it -- if the idle speed doesn't go up = it has a problem. Likewise, when at the correct 1000 RPM warm idle, if you unplug it, you can confirm that the idle speed increases.

The advanced class would be to unplug it (key "off") and measure the resistance between pins 2 and 18 of the throttle microswitch as you have the throttle plate at idle (measure resistance), open the throttle plate by hand (should be infinite ohms), release it back to idle (remeasure resistance), etc. a few times. In the idle position, it should be a just a few ohms resistance maximum. Something like ~30 ohms would be iffy, and hundreds of ohms, or more, definitely bad.

 

Is there an idle valve / regulator in the 328?

 

No, no idle air valve (IAV) is used on Ferrari's implementation of any of the Bosch CIS systems that they used.

 

Hi Steve or anyone I need your help I testet the TPS switch and this is what I got

Terminal 3 and 18
Idle position Reading OL
Full throttle. 0.2 ohm

Terminal 18 and 2
Idle position 3.8 ohm (Soft release)

But 18 and 2 when I open the throttle and let it snap back i get 45 ohms and it slowly goes down to 4 ohms by itself
What do you think
Thanks

 

The 3.8 Ohms on 2-to-18 may work OKish, but the 45 Ohms is almost definitely bad.

 

Thank you I ordered a new one is there a setup

 

You'll see on the throttle microswitch that the mounting ears where the screws go are slots. It needs to be rotated into the position such that the idle switch closes when the throttle plate is in the idle position (i.e., 2 is connected to 18), but the idle switch does not restrict the throttle plate mechanism from reaching its normal idle position.

 

I had the same problem on my 208 turbo and it was due to dirty in the additional air valve, Part No. 118620. It's located under the cooling system expansion tank: on the USA 328 that part is replaced by Part No. 121744, but it usually just need to be cleaned.

Ciao