2.4 coupe idle surge

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Juliasprint
Posts: 7
Joined: Tue Mar 08, 2016 11:48 pm
Dino: Fiat Dino 2.4 Coupe

2.4 coupe idle surge

Post by Juliasprint »

Hello Everyone

In neutral, my idle surges and stays at 1800 to 2000 range... very rarely blipping the gas will bring it down to 1200 or so, only to be hung up at 2k at next stop light..otherwise car runs really well... idle jets were increased to .060 due to low rev stumble, which may have worsened this issue..
Also any brilliant suggestions to get rid of fume smell in the cabin.. I have a new tight oem exhaust, the trunk lead seal is good. Can the fume come in through the slatted vent in the rear pillar on either side?
Thank You
Dario
Posts: 117
Joined: Fri Nov 29, 2013 12:18 pm
Dino: Fiat Dino 2.4 Coupe

Re: 2.4 coupe idle surge

Post by Dario »

Hi, these are two different problems. The exhaust smell needs to be tracked down: likely culprits are a missing shift gator under the tunnel (look under the ashtray to see if you can see a rubber gator over the shift stick); gaps where the exhaust tubes join (especially at the 3in1), I used metal sealing tape over all the joints and this helped a lot; and holes in the firewall where the heater tubes, lines, and wires go through. The rear vents are designed to create a suction, not allow air in. Anyway, by turning the knob to the closed position, it should seal them somewhat using the leather flap that is inside. Are the hoses to the front air vents intact?
For the surge in the idle, I would make first sure that none of the throttle linkages are sticking. Can you bring the idle down by pushing on the pushrods on the carbs? If so, the problem may be there. Another problem source could be the distributer if the advance weights are getting hung up. I would check the advance, linkages, and then think about the carbs: have they been rebuilt? Are the pump diaphragms intact, the jet seats ok, etc...
Good luck,
Dario
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doublegarage
Posts: 212
Joined: Thu Nov 14, 2013 4:22 am
Dino: Fiat Dino 2.4 Coupe
Location: California, USA

Re: 2.4 coupe idle surge

Post by doublegarage »

I would definitely do all the things Dario suggests. Then if that doesn't work:

Look for air leaks around the intake manifold - some suggest testing by carefully spraying starter (ether) spray in a suspected area and listen for change of idle speed.
Sometimes it's possible to mis-tune these carburettors by leaning out the idle mixture too much, then over-compensating by speeding up using the idle throttle stop-screw. This holds the throttles open at all times, exposes the progression holes and then you have the problem. On a DCOE you can remove the progression hole inspection cover and observe with a briight light where the throttle plate is when it starts to move - it should be behind the first hole. If it isn't, then both the idle screw and the progression hole are contributing mixture at idle. (But, I'm not sure that there is such a cover on the DCNF and whether you can see into it)

The fix for that would be to baseline the carb back to standard settings and start tuning again. It does sound like you have one carb that is just more throttled than it should be.

-Richard
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