Alfa Romeo Forums banner

1 - 6 of 6 Posts

·
Registered
Joined
·
246 Posts
Discussion Starter #1
hello to all,

I have a slight surge ( less than 100 rpm) when at idle, fully warmed up.
This was worse ( 200 rpm hot and cold) when I started tracking down the problem, have replaced several hoses, checked the AAV, new donut for
idle speed adjustment. Found a leak ( and repaired) in the hard plastic part of the air intake where it bolts to the valve cover. But this last little bit is escaping me. Any thoughts ?

Thanks in advance
 

·
Administrator
Joined
·
16,621 Posts
What did you find when you checked the AAV? Fully open (or nearly so) when cold? Fully closed when warmed up? I had an AAV that I thought was OK on visual inspection. Looking through it when it was warmed up (I put in a 150 degree oven for ~20 minutes) the internal vane blocked light. Then I tried blowing through it and it would still alow air to pass through. I checked another AAV and found that when its vane was closed it blocked the passage of air. Installed the second AAV and all was well.

There could still be another intake air leak.

Is the TPS (Throttle Position Switch) properly adjusted? With the engine off, listen carefully to the TPS. As you move the throttle off idle, you should hear the TPS click after moving the throttle ever so slightly (1-2 degrees). There are pictures and more info in the L-jet page - see my signature for the link.
 

·
Registered
Joined
·
246 Posts
Discussion Starter #3
Eric,

Thanks for replying so quickly. I followed the L-jet guide as closly as possible.
As for the AAV, I went so far as to disconnect and plug the ports to eliminate that. The TPS "clicks" when the throttle is barely moved so that seems right. I guess I'll have to look around some more for vaccuum leaks. I've gone over everything I can think of at least twice. I even disconnected and plugged the vaccuum advance sensor so as to eliminate that. I'm staring to wonder if i need to look at the afm flap and see if it is out of adjstment.
 

·
Administrator
Joined
·
16,621 Posts
How old is the O2 sensor? A typical life span is about 60,000 miles.

Your '88 should have the 3-wire type - one wire for the sensor and the other 2 for a heating element to keep the sensor at operating temps. If the sensor is at the end of its life or if the heating element isn't keeping it up to temp then the ECU (computer) will go into 'open loop' (ignoring O2 sensor input) which is a slightly richer mixture by default. A slightly rich mixture could explain the surging idle. (and it isn't good for the catalytic converter...)

Look here for info about replacement 3-wire sensors.
 

·
Registered
Joined
·
246 Posts
Discussion Starter #5
The O2 sensor is less than 6 months old. It is a universal 3 wire. I will check it's output next time I have a chance to get back in the garage. Most likely next friday as my work schedule is full till then. Thanks for all your input , i'm sure i'll be back in a couple of days to pic your brain some more :D
 

·
Registered
Joined
·
246 Posts
Discussion Starter #6
Eric you were right on about the O2 sensor, after bringing the engine up to operating temp the voltage reading was only .17 . Looks like I'll be pulling it out and checking the connections. :eek:
 
1 - 6 of 6 Posts
Top