Technical Tipo 1.6 i.e. erratic idle rotation speed

[floring67]

Hi everybody!
There's been some time I have this problem and nobody managed to find the cause. First of all I'll apologize if my English is not very clear.
I have a Tipo 1.6 ie S model 1993, single point injection with Magnetti Marelli Digiplex 2.
It started with too low idle speed when engine was warm, even at the point that engine stopped running. This looked somehow favourised by humidity. Later, the idle speed changed to something erratic, going from 500 to 3000 RPM and ending with engine stopped. After all garages I tried failed to diagnose the problem, I decided to try to do it myself. I used a contact cleaner spray on some plugs; it seemed to work ok after cleaning the crank sensor plugs. Had no problem for a year but now it started again. This time cleaning the contacts did not do the job anymore and I am no longer so sure that cleaning these contacts was really the cure.
It does not seem to be an ignition problem, removing any of the spark plugs contact does not change the behavior. Even cleaning the connector of the Digiplex 2 does not solve the problem.
Unfortunately cannot touch any diagnostics tool except multimeter and mini-oscilloscope, and no garage has it for my car model.
I'm new on this forum, any idea where should I look first? It would be useful if someone has some oscillograms that I could compare.

Thanks
Florin

 

[jonboy739]

have you checked the idle valve on the air flow? i had a problem with mine, it first started cutting out when cold then after a few months would just start revving really high at about 3000rpm. it turned out to be the idle valve which was sticking. i striped it down and cleaned it out which fixed the problem. i dont know where it will be located on the 1.6 but i know it is located on the right hand side of the engine next to the distributor cap on the 2.0 version.

 

[floring67]

Thank you for the answer!
I took a look on the actuator, it seems to work fine. Did clean it though, but with no effect
so far. I didn't have very much time for it either.
But another observation is that when the engine tends to stall, the vacuum meter indicator tends to go on the red zone, as if I pressed the accelerator pedal. More the engine stalls, more it goes on the red zone. This also makes me think to one of the sensors.
Any data for what should I measure on the lambda sensor, air pressure sensor or temperature sensor? I know the pulley sensor should have 700-900 ohms.

 

[floring67]

Ok, after some more study I noticed there is no real vacuum sensor but it's calculated according to the throttle position; so maybe the throttle position sensor can be the answer to my problem. My question would be if anyone knows if this sensor is the same that drives the vacuum meter?
Data on the temperature and lambda sensor could still be useful.

I guess nobody knows any diagnostic tool for the ECU, got no success in searching all the web for it, but it can't hurt asking again.
I know it is 8051 based and therefore it uses RS232 3 wire protocol since 8051 has an incorporated serial interface.