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Re: My 1989 22re idle surges when warmed up and brake...
Check the vacuum hose from the engine to the power brake vacuum reservoir, it make be loose or cracked and will cause an erratic idle because of the vacuum leak. Please rate this answer, thanks.
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The power brake booster runs on engine vacuum to provide the power assist. Since it surges at idle and you mention that hard brake pedal application causes the surge as well, along with the knowledge that the engine was recently replaced, I'd be looking for a vacuum leak somewhere.
If you had the engine installed by a reputable shop, you should take it back to them assuming it started doing this just after the engine was installed. If they have a smoke machine for locating vacuum leaks, that should make the search even easier.
www.jaguarforum.com/showthread.php?t=54266 Mar 3, 2013 - I recently bought a 1993 6.0 V12 XJS and when it is started from cold it runs ... to 1300 RPM so it wants to surge forward when braking which is strange. ...Classics · XJS 3.6,4.0,5.3 & 6.0; 6.0 V12 XJS High RPM When Warm ... You might want to adjust the aux (extra) air valve to bring the idle speed down.
When idles surges its due to false air, The MAF (mass air flow) calculates the amount of air and responds to the proper amount of fuel, When you get false air such as a broken PCV valve,or ruptured vacuum hose the idle increases and you get the surge that you are describing,Your basically out of fuel control .
The idle adjustment screw in throttle body has carbon build up on its tip.need to remove screw clean depoisits off tip,carbon in idlescrew port(with carb clean) re-install idle screw,seat it,then back out 1 1/2 turns.start car and hold at higher idle to blow out carb. clean &deposits out of throttle body then recheck for surging once warmed up.
block off vacuum hose to brake booster and see if idle returns to normal if it does you need new brake booster has hole in diaphram internally some times slight hissing noise is evident in cab when pressing brake pedal to section where engine surges or idles high. also check for fuel leaks from hoses if you can smell fuel in engine bay while running and engine warm some leaks only leak while running and hot
check the swiches at the brake pedal their should be two. one for brake lights and one for transmission dump valve it prevents the engine from loading up at lower rpm. ie stoping at lights while in drive
1990 22re same problem surge when pedal was depressed thought it was booster or check valve still didnt fix it i even put a brand new booster on it just to make sure still no fix it finnally went away on its own for about a month now it does it just sitting at an idle with out the brake pedal depressed traced all vaccum lines no problem there and still have no clue
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