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 Post subject: “Jerky” throttle
PostPosted: Sat Jan 05, 2019 11:57 pm 
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Joined: Tue Jan 01, 2019 5:36 pm
Posts: 14
Model: 924
Hi guys, went for a ride in a 924 today, was great fun.
However, when accelerating it had a tendency to jump or jerk, as if the throttle was intermittent, I thought perhaps it wasn’t get a smooth constant fuel flow or something, maybe a clutch slip? But felt a lot more like it was in the throttle somewhere.
It had the same feel as a new driver doing the kangaroo thing. It wasn’t a constant thing, just did it a few times. Mostly under acceleration.
Is this a common fault?
Any ideas anyone?
I’m thinking of buying it but I want a smooth drive! And don’t want to spent a fortune on fixing it.

Cheers all.


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 Post subject: Re: “Jerky” throttle
PostPosted: Sun Jan 06, 2019 9:44 am 
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Joined: Mon Jan 04, 2010 11:24 pm
Posts: 16864
Location: Gloucester
Shouldn't do anything like that, could be a misfire under load or sticky parts in the fuel distributor/ air flow meter. Revs would rise if clutch is slipping.

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1984 924 N/A RUBY RED METALLIC - 924 of the Show, National 2018
1988 924S Guards Red - sold
1986 924S Guards Red - sold
1984 924 N/A Black - sold
1980 924 LE MANS#1 - sold
1980 924 LE MANS#2 - sold
1977 924 Martini - sold


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 Post subject: Re: “Jerky” throttle
PostPosted: Sun Jan 06, 2019 12:03 pm 
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Joined: Tue Jan 01, 2019 5:36 pm
Posts: 14
Model: 924
Good point in the clutch.
The revs certainly dropped out when it did it. Not for long. Just a fraction of a second at a time in a burst.


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 Post subject: Re: “Jerky” throttle
PostPosted: Sun Jan 06, 2019 12:10 pm 
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Joined: Sat Jan 30, 2010 11:13 pm
Posts: 15405
Location: Somerset
Model: TheOnly Way Is Turbo
Could be many things in the ignition and fuel system. Start at the coil through to spark plug first. Broken wire, rotor, dizzy, leads, plugs. Could be something super simple like a loose lead not seated correctly.

Then fuel system. Could be anything from dodgy fuel pump(s), dirty fuel filter, gummed up dizzy to knackered or dirty injectors. Has the car been driven much recently? How much? Old fuel? Italian tune up needed?

When was the last full service when all consumables were replaced?

Needs physical diagnosis not remote. Sounds like one or more cylinders are misfiring under load. Spark plug colour may give a clue to which one. May be more sooty. Then methodical fault finding. If it only happens on acceleration, then it could far harder to find. Maybe really obvious once rooting around

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1980 924 Turbo Series 1 - Alpine White & Guards Red
Omega forged pistons, lightened and balanced bottom end, ARP studs + Cometic MLS HG, Piper fast road cam, K27/26 3257 hybrid turbo, 951 ducted FMIC, Custom intake manifold, Mittelmotor dizzy & cam pulley, Adj boost - dyno’d at 225bhp @ 1.0bar on previous CGT turbo, Engine datalogged and on boost fuel enrichment managed with Zeitronix ZT2 & Phormula KS4 knock sensor, 944 turbo all alloy radiator, Hayward & Scott custom tapered race exhaust, GAZ Gold coilovers, Fuch'ed up, Quaife LSD
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 Post subject: Re: “Jerky” throttle
PostPosted: Sun Jan 06, 2019 12:21 pm 
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Joined: Tue Jan 01, 2019 5:36 pm
Posts: 14
Model: 924
Carrera RSR wrote:
Could be many things in the ignition and fuel system. Start at the coil through to spark plug first. Broken wire, rotor, dizzy, leads, plugs. Could be something super simple like a loose lead not seated correctly.

Then fuel system. Could be anything from dodgy fuel pump(s), dirty fuel filter, gummed up dizzy to knackered or dirty injectors. Has the car been driven much recently? How much? Old fuel? Italian tune up needed?

When was the last full service when all consumables were replaced?

Needs physical diagnosis not remote. Sounds like one or more cylinders are misfiring under load. Spark plug colour may give a clue to which one. May be more sooty. Then methodical fault finding. If it only happens on acceleration, then it could far harder to find. Maybe really obvious once rooting around


Cheers, will have a look. Was still happening driving normally, just seemed to do it more when you opened up the throttle.
Hasn’t been used much at all lately.


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