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Old 09-03-2001, 02:42 PM
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Join Date: May 2001
Posts: 301
I'm mystified by these 420 problems


The car..... .......1991 420SEL
The mileage......,161,000 well maintained

The main problem......While sitting at idle (600rpm) in park I press lightly on the accelorator brining the revs up to 1000. it will stay at 1000 for a few seconds then suddenly fall off to maybe 400 then quickly go back to 1000. It will also do this if the car is coasting at 5-10 mph and I step lightly on the pedal. It is kind of a surging feel. It's not a faulty tach, you can feel the dips and see the oil pressure react as well.

A smaller problem... Turning the wheel while stoped or at low speed makes a squeek that sounds like rubber against metal. I thought I remember someone writing about a rubber bushing that I could lubricate.

Thank you for your opinions

Last edited by fredsegal; 09-23-2001 at 02:38 PM.
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Old 09-04-2001, 01:32 PM
mburman's Avatar
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Join Date: Jul 2001
Location: Tampa, FL
Posts: 69
Sounds to me like an air flow meter problem or mixture problem. Pull your spark plugs and see if they are clean and properly gapped. Check a chilton manual for how to read your spark plugs to see if you're running too rich or too lean. I don' t know if you have an air flow meter, but it could be the cause of your problems too. Maybe someone else has some other suggestions.

About your steering... I don't know anything about a bushing, but check your power steering fluid level and the tension on the belt. you should be able to push the belt 1/2 inch at its longest run.

Good Luck!
71 MGB
76 450SL

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Old 09-04-2001, 02:08 PM
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Join Date: Jul 2001
Location: SoCal
Posts: 1,303
The FI has a separate idle circuit switched in when the throttle closes. The ECU sets the idle speed by adjusting the injector flow. When the throttle opens back up, the switch opens, returning the ECU control to running mode, where fuel flow is determined by airflow. It sounds as though there may be an incorrect adjustment affecting the switchover - it may occur at too wide a throttle opening.

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Old 09-08-2001, 09:09 PM
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Join Date: May 2001
Posts: 301
I'm thinking I may have a leaky injector. Can I change them 1 at a time or must it be all at once?
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Old 09-23-2001, 02:43 PM
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Join Date: May 2001
Posts: 301
I have also noticed that if the a/c is on when I start the car I can smooth the slightly rough start up idle by turning it off. Conversly if the a/c is off at start up, the idle is smoothed by turning it on. What the heck?
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Old 09-23-2001, 06:27 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Well, Steve might have something with that throttle switch even though the explanation needs some serious help.

The mixture while altered electronically by the EHA is always controlled by the airflow meter working on the fuel distributor. The airflow at idle is managed by a second small throttle (the idle air valve). The air that it lets into the motor still passes and is measured by the airflow meter.

The idle switch is a signal used by the idle controls to tell them that the throttle is closed and to go ahead and feedback control the idle (feedback control means that if the idle is too low it adds air, if too high it shuts down air... it reacts to the condition). One must realize that if the idle is too high the valve shuts down. If this were to occur as one drives (the speed is high so the valve is shut) then the valve would be shut when you rapidly realeased the throttle and the engine would die. When the system is off idle the controls hold the valve in a slightly larger setting waiting for idle again and time to control.

Another function of the idle switch is to tell the KE controller that one has released the throttle. If the rpms are high enough the the fuel control shuts down the mixture for something called decel cut-off.

I would monitor these controls and see which are varying during the event.

I would also watch current through the idle controller as the OVP relay can cause the current to go low and leave a very low idle.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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