Stock 1980 FI idle surge

The forum for all of your technical questions on your classic FIAT autos
Post Reply
User avatar
PhillySpider
Posts: 371
Joined: Wed Aug 31, 2016 9:38 pm
Last Name: Gomolinski
First Name: Mike

Stock 1980 FI idle surge

Post by PhillySpider » Sun Jul 01, 2018 10:28 pm

Hey Folks, starting to chase an idle surge that I was hoping my planned maintenance items would take care of. The car has always surged warming up from about 400 to 800 rpm. Warmed up you hear and see a slower surge on the tach...about 850 to 1,000 rpm, basically ilding strong around 900-950 and occasionally dropping for a moment every 10 to 20 seconds.

In first gear it was hard to give a light throttle and not buck a bit. Since swapping the fuel filter this evening she is smooth in first FWIW. Post filter swap I'm still seeing surging cold and warmed up, but not as frequent.

What's been done so far in the last year:
Timing belt
Alternator belt
Tstat
dizzy cap and rotor
plugs and wires
water pump
Heater core / valve
New radiator hoses and radiator temp switch

Where to go from here, or is some surging normal and to be expected.

Thanks!
"Life is what happens while you're busy making plans"
Garage:
1980 FI Spider 2000 MT
2014 Audi A4 MT
2014 Mercedes C300 AT
User avatar
rridge
tremila club
Posts: 3358
Joined: Sun Jan 24, 2016 9:18 pm
Last Name: ridge
First Name: richard

Re: Stock 1980 FI idle surge

Post by rridge » Mon Jul 02, 2018 6:58 am

Surging at idle is often related to poor mixture control. Check that the O-ring on the idle air screw is still sealing. Set the idle per the manual. Then check that the throttle position switch is properly adjusted.
Richard
'81 Turbo Spider
Rockville, MD
User avatar
bartigue
cinquemila club
Posts: 5767
Joined: Sat Jan 23, 2016 11:49 pm
Last Name: Artigue
First Name: Bradley
Contact:

Re: Stock 1980 FI idle surge

Post by bartigue » Mon Jul 02, 2018 7:48 am

Surging is almost always an air leak. Check the usual spots. then check the unusual ones. Something as simple as the electronic ignition vacuum canister being bad can cause surging.
-----------------------------------------------------------
Brad Artigue
1982 Spider 2000
I've restored, worked on, sold, bartered, and bled for:
1970, 1979, 1980, 1981, 1982 124 Spiders -- 1969, 1970 850 Spiders -- 77 X1/9
http://fiat.artigue.com
User avatar
lanciahf
Posts: 656
Joined: Sun Jan 24, 2016 7:37 pm
Last Name:

Re: Stock 1980 FI idle surge

Post by lanciahf » Mon Jul 02, 2018 12:30 pm

Mike, while the car is idling spray short bursts of brake clean around the rubber seals and see if the idle changes.
If the idle changes then you found the leak.

Also check the underside of the big rubber air hose & aav hose.

Did you ever change your fuel hose and seals at the injectors?

Ralph
Ralph DeLauretis
2013 Fiat 500 POP
1984 Pininfarina Spider
Recovering Scorpion Owner.
User avatar
jseabolt
seimila club
Posts: 6057
Joined: Sun Jan 24, 2016 7:27 pm
Last Name:

Re: Stock 1980 FI idle surge

Post by jseabolt » Mon Jul 09, 2018 5:49 pm

When you mean surging, do you mean the idle speed is going up and down in a perfect rhythm? I had an X 1/9 do that after I gave it a complete tuneup with a new oxygen sensor. In this case afterwards the idle speed jumped to around 2000 rpms . Then it seemed after a few minutes (I suppose the O2 sensor getting heated up), it would lope up and down. It ran fine otherwise.

I finally traced it down to the short cable between the valve cover and throttle body. There is supposed to be a bit of slack in this cable but someone took all the slack out of it so the throttle body was cracked open. Instead of using the adjustment bypass screw. Not only that the TPS was also out of adjustment.

I realize the Spider does not have this short cable but what seemed to happen was someone monkeyed with this car trying to get the car to idle instead of giving it a much needed tuneup. Fuel consumption went from 20 mph to 35 mpg afterwards.

I can unplug the O2 sensor on my Spider and it doesn't seem to make it idle any different but for some reason on this X 1/9, the high idle speed caused the engine to lope. Maybe in conjunction with the misadjusted TPS the new sensor was detecting an abnormal amount of fuel and was trying to cut back on the mixture then turning around and throwing more fuel in a viscous cycle. I'm not real sure what was going on. I just know once I lowered the idle speed it took care of the lope.

I know this doesn't pertain to your car but on carburated engines, I have seen a blocked fuel bowel vent do the same thing. That was with one of those old Zenith carburetors.
User avatar
rridge
tremila club
Posts: 3358
Joined: Sun Jan 24, 2016 9:18 pm
Last Name: ridge
First Name: richard

Re: Stock 1980 FI idle surge

Post by rridge » Wed Jul 11, 2018 5:56 pm

To follow up on Seabolt's point, it never hurts to check the TPS after adjusting the air bleed and throttle position screws. There's two switches in the TPS. One senses full throttle and added enrichment. The other senses closed throttle and cuts the fuel above a certain rpm (overrun) and takes the O2 sensor out of the control loop at idle to prevent "hunting". You can hear the switches click as the throttle plate moves to the ends of its range. A VOM on the connector will confirm the switch operations. Middle contact is the common wire.

If adjustment is needed, be careful not to apply much force to screws that loosen and allow the TPS housing to rotate. They are small diameter and easily sheared if corrosion has developed in the threads of the throttle body. Let penetrating oil loosen things up overnight.
Richard
'81 Turbo Spider
Rockville, MD
User avatar
PhillySpider
Posts: 371
Joined: Wed Aug 31, 2016 9:38 pm
Last Name: Gomolinski
First Name: Mike

Re: Stock 1980 FI idle surge

Post by PhillySpider » Sat Jul 14, 2018 12:42 am

Thanks folks...going to locate and check out the tps. Regarding the 02 sensor...that's likely the original to my knowledge. Guessing I should figure out how to check that as well. I'm sure it's covered in detail here. Love this place, thanks for the help!
"Life is what happens while you're busy making plans"
Garage:
1980 FI Spider 2000 MT
2014 Audi A4 MT
2014 Mercedes C300 AT
User avatar
jseabolt
seimila club
Posts: 6057
Joined: Sun Jan 24, 2016 7:27 pm
Last Name:

Re: Stock 1980 FI idle surge

Post by jseabolt » Sat Jul 14, 2018 4:38 pm

PhillySpider wrote:
Sat Jul 14, 2018 12:42 am
Thanks folks...going to locate and check out the tps. Regarding the 02 sensor...that's likely the original to my knowledge. Guessing I should figure out how to check that as well. I'm sure it's covered in detail here. Love this place, thanks for the help!
You can hook a voltmeter to the O2 sensor. Pull back the connector and test voltage. If it's working it should cycle between 0 and .9 volts. If it's zero then its dead. You can also unplug it from the ECU and it should at least read something between 0 and .9 volts. Make sure the engine is heated up.
Post Reply

Who is online

Users browsing this forum: No registered users and 6 guests