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I took a drive last night and my brake assist was at first intermittent. By the end of the 25-minute drive, the brake assist was totally gone, plus the car was idling around 1500rpm or more. I'm assuming it sprang a vacuum leak somehow. I think I'm hearing an unfamiliar whistling noise in the engine bay but can't pinpoint it. Any ideas?
 

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It sounds like you sprung a leak in the vacuum hose for your brake booster. I'm not familiar with the Esprits so I can't tell you where to look but you're looking for a large vacuum hose, about 5/8" or 15 mm diameter. The hoses typically fail near where they connect to the engine intake, where the heat from the engine decays the hose and they'll start cracking. Often you can just cut off the bad part of the hose and plug it back in, good as new. If you can pinpoint that new whistling noise I'm sure you'll find the problem.
 

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As you have a V8 ? (always helps to put your year in the question) your brake assist is electric not Vacuum so in theory they are not related, but its a Lotus so anything is possible :D The higher Idle RPM could be the ECU compensating for something, such as a Vacuum leak at the intake manifold.
 

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The V-8's use a vacuum booster. The "electric" stuff is the ABS. It *could* be a hose problem but it can also be a leaking booster. Plug the hose by the motor and see if the noise goes away. If it does, pull the hose by the booster and plug it and see if the noise goes away. I don't think on the V-8's a vacuum leak is going to give you that high an idle unless it is in the idle motor system. Vacuum leaks are best found by using a smoke machine. It makes the invisible, visible.
David Teitelbaum
 

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1988 Esprit Turbo
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Waiting for confirmation of year/model....
 

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The V-8's use a vacuum booster. The "electric" stuff is the ABS. It *could* be a hose problem but it can also be a leaking booster. Plug the hose by the motor and see if the noise goes away. If it does, pull the hose by the booster and plug it and see if the noise goes away. I don't think on the V-8's a vacuum leak is going to give you that high an idle unless it is in the idle motor system. Vacuum leaks are best found by using a smoke machine. It makes the invisible, visible.
David Teitelbaum
The service/parts manual show a Vacuum booster on pre-98 MY while later V8's have an electric vacuum pump (see Atwells post above re: model year)
 

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All V8's used a vacuum booster. Vacuum source was a hose to the manifold.
Travis,
That’s actually what I thought, so I just pulled up the parts manual for a quick look and found two options? I thought it odd too as I could hear my S4 electric pump no problem and no such noise on my V8 (which is new to me so I haven’t looked in to the brakes......yet:D) curious though where on the manifold? as its under positive pressure (from turbo boost) so where does it pull a vacuum? (As this connection could be the original posters issue)
 

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When you are under boost the check valve holds vacuum for the booster and typically you are not using brakes when under boost. The booster can hold enough vacuum for 1-2 pumps of the brake pedal. A bad check valve can cause braking problems under boost so it should probably be checked to make sure it is working, besides checking for vacuum leaks. There is an "operational check" of the servo in section JG page 17. The hose supplying vacuum to the servo comes off the front, right side of the motor, a large black hose. Refer to section ED page 65. #23. BTW, there is a vacuum reservoir to supply vacuum during periods of boost for the climate controls. In actuality you really are not under positive pressure (boost) very often or for very long so typically you would not notice any fluctuation in your vacuum controls. On cars with vacuum advance, it is usually disconnected when you install positive aspiration. On a Lotus V-8, ignition is controlled electronically by the ECU so you don't need vacuum for it. The evap system is not operating during boost so it doesn;t mind the lack of vacuum for a short time.
David Teitelbaum
 

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When you are under boost the check valve holds vacuum for the booster and typically you are not using brakes when under boost. The booster can hold enough vacuum for 1-2 pumps of the brake pedal. A bad check valve can cause braking problems under boost so it should probably be checked to make sure it is working, besides checking for vacuum leaks. There is an "operational check" of the servo in section JG page 17. The hose supplying vacuum to the servo comes off the front, right side of the motor, a large black hose. Refer to section ED page 65. #23. BTW, there is a vacuum reservoir to supply vacuum during periods of boost for the climate controls. In actuality you really are not under positive pressure (boost) very often or for very long so typically you would not notice any fluctuation in your vacuum controls. On cars with vacuum advance, it is usually disconnected when you install positive aspiration. On a Lotus V-8, ignition is controlled electronically by the ECU so you don't need vacuum for it. The evap system is not operating during boost so it doesn;t mind the lack of vacuum for a short time.
David Teitelbaum
Yup,
All makes sense now, and i believe the two pump options on the V8 were for the HVAC vacuum, not the brakes (same as the S4 where the Vacuum pump does not have anything to do with the brakes) I haven't driven my V8 enough to even get aquantied with all the systems yet, but the AP brakes are awesome! found that the servo vac hose connected to the front right bank of the manifold (attached number 23)
 

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