2nd Generation Specific (1986-1992) 1986-1992 Discussion including performance modifications and technical support sections.

S5 rebuild throttle and idle problem

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Old Jul 8, 2019 | 10:22 PM
  #1  
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TN S5 rebuild throttle and idle problem

So I just finished my rebuild about a week ago and have been frequently running engine to try and warm up compression. I've heard that idling it a couple hours will soften up the idle and make the car start easier. My car certainly starts easier, on cold and full battery charge starting is very easy and throttle responds instantly, though it does not idle for a short minute. Starting hot is still a bit difficult but with charge it's still doable without messing with oil. As engine warms up from cold start, it gets better at idling but worse at responding to throttle until giving throttle actually drops revs. If I turn it off and on again throttle revs fine for a couple seconds, but it stops after that. I've looked around and noticed this case might have been somewhat unique, and am just looking for a place to start looking. Anyone have a clue about this

?
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Old Jul 8, 2019 | 11:08 PM
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Have you checked your fuel pressure? Do you have a new fuel filter?
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Old Jul 8, 2019 | 11:16 PM
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A friend of mine changed fuel filter and did fuel work back in February, car has been sitting ever since while rebuild happened.
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Old Jul 9, 2019 | 01:58 PM
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So, when warmed up you push the gas pedal and rpm drops?

I would check fuel pressure while this is happening. Have someone push the pedal while you observe.
I would also check compression if it hasn't been checked already. It's easier to face the music right away.

Post back with fuel pressure readings, fuel pressure readings during bogging and compression readings(warmed up). That info would help a lot.

This could also be an ignition issue.

Last edited by Rotary Alkymist; Jul 9, 2019 at 02:01 PM.
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Old Jul 9, 2019 | 06:23 PM
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Still waiting on fuel pressure tester to come in but I checked compression on it and the compression's sitting around 60psi. I've been running it on and off for about a week probably 2 and a half hours total on used plates. Does compression usually get better as you run a rebuild?
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Old Jul 9, 2019 | 07:11 PM
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Also there is an exhaust leak might be a contributor
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Old Jul 10, 2019 | 11:41 AM
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Vacuum hose on fuel regulator was not connected... WOW I'm a dumbass
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