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Globedog12
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Joined: April 11, 2024
Posts: 223
Location: Atlanta, GA
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 Posted: Mon Jul 28, 2025 6:51 pm Post subject: 76 2.0 Fi with jumpy idle |
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I’m trying to figure out my idle problem. It varies from 850-1000 rpm. Drops down then jumps up on repeat.
Current:
Valves at .006
28 degrees before tdc all in with hose removed.
Idle screw out about 2 ¾ turns to get around 950
Dwell 49
I’ve addressed a vacuum leak at the aar and throttle body gasket no change.
Currently the brake booster has been holding 10” vacuum for ½ hour. Check valve is ok.
I’m going to do another smoke test in the engine compartment just to be sure but last time I think I got everything.
Wondering what my next steps should be? My first thought was checking fuel pressure to make sure I’m not over pressurizing the fuel rail and maybe pushing too much fuel through the fuel injectors creating rich then not then rich…
After that I’m at a loss. Anyone have any wisdom to give me?
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1976 VW Type 2 Original fuel injection |
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SGKent 
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Joined: October 30, 2007
Posts: 42752
Location: at the beach
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| Posted: Mon Jul 28, 2025 7:00 pm Post subject: Re: 76 2.0 Fi with jumpy idle |
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what do you know about the engine and camshaft?
Also have you done a cylinder balance test to see if one cylinder is dropping out?
Have you watched the timing when the change occurs to see if it is stable?
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"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin |
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Globedog12
Samba Member
Joined: April 11, 2024
Posts: 223
Location: Atlanta, GA
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| Posted: Mon Jul 28, 2025 7:20 pm Post subject: Re: 76 2.0 Fi with jumpy idle |
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| SGKent wrote: |
what do you know about the engine and camshaft?
Also have you done a cylinder balance test to see if one cylinder is dropping out?
Have you watched the timing when the change occurs to see if it is stable? |
I know very little about the history of the engine and camshaft. Top end was done by me recently. New cylinders pistons and heads. The number one piston had a bad leak at the head and the piston had some damage. Everything ccd compression ratio set to 7.3 The timing jumps with the rpm’s. Not sure what you mean by cylinder balance test. I’ve pulled each fuel injector connector to see if rpm drops with each (it does) but I haven’t watched to see if leaving one cylinder disconnected makes rpm stable. Reconditioned distributor, new cap rotor and wires.
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Wildthings
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Joined: March 13, 2005
Posts: 52460
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| Posted: Mon Jul 28, 2025 7:23 pm Post subject: Re: 76 2.0 Fi with jumpy idle |
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You did set the timing at >3500 rpm, didn't you?
If you haven't done so add some FI cleaner to your tank. |
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Globedog12
Samba Member
Joined: April 11, 2024
Posts: 223
Location: Atlanta, GA
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| Posted: Mon Jul 28, 2025 7:33 pm Post subject: Re: 76 2.0 Fi with jumpy idle |
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| Wildthings wrote: |
You did set the timing at >3500 rpm, didn't you?
If you haven't done so add some FI cleaner to your tank. |
I did but the fi cleaner is probably a good idea. They sat in a plastic bag for a couple months while I did the top end.
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SGKent
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Joined: October 30, 2007
Posts: 42752
Location: at the beach
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| Posted: Mon Jul 28, 2025 9:05 pm Post subject: Re: 76 2.0 Fi with jumpy idle |
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a cylinder balance test is where you gently pull each plug wire with a dry rag at the distributor and verify each cylinder is firing.
The timing should be stable at idle. It should not move around. When the engine gets up between 1000 and 1100 it will start advancing. You want to be sure that the ported vacuum is on the distributor. The constant plenum vacuum goes on the fuel pressure regulator and the decel valve.
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