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Amedee, Former ASE Master Tech
Category: Car
Satisfied Customers: 24123
Experience:  ASE certified tech advanced level specialist. Wisconsin certified emissions state inspector
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I own a 1986 Bentley Eight..sitting..high revs..engines

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I own a 1986 Bentley Eight. My problem is that although I can get her to start, but not to run on idle even after say 5 minutes of sitting there maintaining high revs !
I wonder if there is a simple answer as I am not in any ways good with engines . Maybe the automatic choke is not working. Even so if it were not surely she would tick over after getting warm with the temp dial reading at 3 oclock !
Any ideas out there as she is due for an MOT next week but I dont know how I will get her there as I would not want to engage the gears when the engine has to run at such high revs !
Monty Nunn
Hello there!

Did you say that the engine is reving high at idle? Does the rpm fluctuate when its trying to idle?
Customer: replied 6 years ago.

no the engine is not reving at idle . in fact it will not idle. If I take my foot off the excellerator pedal after say 5 mins of reving higher than idle it just dies , but I can just 'catch' it if I push hard to the floor to get it back.


You might have an air or a vacuum leak. This is very common! Open the hood and listen for a hissing sound when the engine is running.
Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow.
If it is hard to pinpoint take some brake cleaner or starting fluid around the intake manifold and vacuum lines and see if the engine stumbles or if the idle is affected. Be extremely careful when doing this!


Also, your throttle body may be carboned up and need to be cleaned! This can cause all sorts of idle and hesitation problems. This is caused by the throttle plate not seating properly. The First thing i would do is clean out the throttle body with some throttle plate and intake cleaner and a small brush. Another common cause would be the Idle Air Control motor. This is very common on older cars. The IAC motor gets lazy and cant keep up with the fast idle changes. Also when the IAC motor is out, I rec to check the passages for carbon build up. If they are plugged they need to be cleaned out.


Check for the following conditions:


Poor connection at PCM or IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
Damaged harness. Inspect the wiring harness for damage.
Restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element, or foreign objects blocking the air intake system.
Throttle body. Check for objects blocking the IAC passage or throttle bore, excessive deposits in the IAC passage and on the IAC pintle, and excessive deposits in the throttle bore and on the throttle plate. Check for a sticking throttle plate. Also inspect the IAC passage for deposits or objects which will not allow the IAC pintle to fully extend.
Vacuum leak. Check for a condition that causes a vacuum leak, such as disconnected or damaged hoses, leaks at EGR valve and EGR pipe to intake manifold, leaks at throttle body, faulty or incorrectly installed PCV valve, leaks at intake manifold brake booster hose disconnected, oil filler cap, oil level indicator loose or missing, etc..

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