Idle adjustment on a 72 CSi

[axco]

The idle adjustment on the throttle body has almost no effect on the idle speed of the engine. To test this further I blocked off the auxiliary air supply from the warm-up circuit after the engine had warmed up. The car immediately died after the restart. I had to back out the idle adjustment screw almost all the way to keep the car running at idle. Backing out the idle adjustment screw all the way also produced a loud suction noise at the throttle body. Any idea on what is going on here?

 

[lloyd]

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The idle adjustment on the throttle body has almost no effect on the idle speed of the engine. To test this further I blocked off the auxiliary air supply from the warm-up circuit after the engine had warmed up. The car immediately died after the restart. I had to back out the idle adjustment screw almost all the way to keep the car running at idle. Backing out the idle adjustment screw all the way also produced a loud suction noise at the throttle body. Any idea on what is going on here?

This is not much of an answer, but you might consult the manual because there are lot of things at play given your very general description. Also, this forum contains several posts concerning Djet diagnostics. Describing how or when this condition first developed might also aid in any long distance diagnosis.


Assuming your ignition system is properly functioning, (e.g., ignition timing is not seriously retarded or advanced) have you tried adjusting the potentiometer on the ECU? In short, this can affect idle mixture, assuming all other systems are in working order. (See Slow running adjustments - below.)


Next, is the electrical connection to the intake manifold sensor (on the forward part of the "log") intact? If disconnected/broken, this will likely richen the mixture. All of the temp sensors, (near the auxiliary air valve) and their connections can affect engine operation, so it is always a good idea to check wiring condition and connections.


You mention "blocking off" the auxiliary air valve, but what about the cold start injector? Again, assuming that your ignition system is properly functioning, is it possible that your cold start valve/injector is not switching off and still supplying the engine with fuel after the engine is at normal operating temperature? This would richen the mixture to the point where additional air is necessary to maintain an air/fuel balance upon which the engine can function. Since the cold start injector is always pressurized by the fuel pump, leaking is not uncommon. Unplugging the electrical connection may not terminate any leak if the injector is stuck open or even slightly open.

Other (non-ignition-related) possibilities include a maladjusted fuel pressure regulator and a failing pressure sending unit.


HTH :wink:

 

[axco]

Thanks lloyed for the reply. I bought this car about 3 years ago. Once warmed up, the car drove fine however I suspected it ran a little rich. But I did not like the throttle response when accelerating. There was always a hesitation even when the engine was warmed up. Starting from cold the car was almost not drivable, stumbling and hesitating when I pushed down on the gas. Over the following month I checked all those things which one can check with the manual and an instrument. So past winter I had the injectors cleaned and checked and the control unit with the MPS checked at a Bosch facility. However the problems mentioned are still is there. That's why I decided to block of the auxiliary air hose and yes I also disconnected the cold start injector valve. By blocking of the auxiliary air hose I must somehow affect the air/fuel mixture. I had checke the auxiliary valve before and I know it closes when the engine is warmed up (or at least the way I tested it in a pot of hot water).

 

[Stevehose]

Have you checked all possible vacuum leak areas?

 

[lloyd]

Having established that you know your way around an engine bay, my off-the-cuff suggestions probably miss the mark.

Hesitation can be caused by many things including, a funky or maladjusted throttle position switch and even low fuel pressure. I would assume you checked both. Also I would recommend perusing through the many posts dealing with hesitation. http://www.e9coupe.com/forum/showthread.php?t=16054; http://www.e9coupe.com/forum/showthread.php?t=12996, etc.

It might be helpful to know more about the mechanical condition of your engine and any modifications, including ignition and cam changes. Aside from idle issues and hesitation, does your engine run smoothly?

Is your cam timing altered? Valve lash properly set? What type of spark plugs are you using and what are their gaps?

Retarded ignition timing can also provide underwhelming performance. With respect to many purists, the factory recommended settings were based on an unworn, well-maintained engine using pump 1970's pump gas. Following the recommendations to the letter with today's fuel can result in annoying "pinging." So, some retard the timing to avoid the noise, but at the expense of a little performance. Your specific engine may be in better -than-factory-new mechanical condition, but if your ignition timing is retarded, its going to have reduced performance. Have you tried advancing the ignition timing slightly?

Good luck.

 

[sfdon]

I would suggest a vacuum test on the manifold pressure sensor over by the brake booster.
I would also suggest with the key set to on not run set it to on and then manipulate the throttle while listening to the injectors.

 

[axco]

sfdon, the MPS was replaced with a factory rebuilt unit and tested with the control unit over the winter (I sent both to Germany), a $600 expense which as it turns out, I could have done without. I did do the test you recommended of the throttle switch. All injectors fire as I move the switch. I also removed the cover and inspected the switch. The only complaint I have there is how sloppy the switch actuation shaft fits thru the bushing on the throttle body cover. Other than this the switch looks fine.
At higher RPM, the motor runs fine, my issue is idling and the transition when asking for power. By disabling the cold start auxiliary air intake and disconnecting the cold start injector why does the well warmed up motor not retain an idle? Why can't I increase the idle RPM over 900? And why does the the motor almost die if I open the throttle and quickly let it go?

 

[sfdon]

Pull the valve cover and prove to yourself that the crank, cam and flywheel are all at TDC.
That means putting a spot of paint on the TDC mark on the flywheel and another spot on the timing mark 7 teeth away.
Adjust your valves while you are in there.
Make sure your oiler bar bolts are snug too.
Only roll the engine clockwise when you verify TDC.
Fire up the car and set timing now- about midway between the marks for idle and at the second mark at 2200 rpm.

Difficulty holding idle and difficulty running up the rpm range are usually mixture related.
Because timing can affect mixture its best to get it out of the way first.
I've seen a few cars come in set 22 degrees retarded.

 

[sfdon]

BTW- changing 2 variables at the same time is the road to hell
What happens when you apply a set of vise grips to the fuel line to the cold start injector only
And what happens when you disable the air valve only?