MFI Cold Idle Issue...can anyone help?

[Gary R]

I recently had my Throttle Bodies rebuilt (by Eurometrix). they came out beautiful. I put them back on the car. Followed the 10 steps in the Check Think Repair sequence. Everything is correct. I could not get the idle below 1200 after the car fully warmed up.

I did some reading on earlier threads and found a similar issue where the recommendation was that the MFI pump was too lean. After the car was fully warmed up, I found by clicking about 6 clicks clockwise that on the 6th click the idle dropped to 1000 RPM and by adjusting the air screws on the throttle bodies slightly the car would idle (fully warmed up) at 950. If I turn the lean/rich screw on the pump back lean one click (counter clockwise) the car would idle back up at 1200 and the air screws on the throttle bodies could not get the idle back down. I moved it back 1 click rich and idle was again at 950 and balanced the vacuum on each stack at idle.

The problem is that when the car is cold, it idles too low. If I lean up the pump back to where I started, the car will idle fine when cold, but as soon as it warms up, it will not idle under 1200 RPMs.

My cold start is disconnected because my cold start sprayers are not lined up correctly. I am under the impression that these only spray a shot to start the car. Is this correct?

Also I tried to use the hand throttle, but it will not keep the idle high enough.

Am I on the right track with the lean/rich screw on the pump? If so, what do I need to do to get the car to idle properly when the engine is cold?

Thanks for your input.

Sincerely,

Gary
1970 911E Targa #733

[edmayo]

Where is your ignition timing set? Did you adjust the pump control rod to 114mm, all other linkage must be disconnected from the cross bar, the 114 mm pump rod attached, THEN the main rods to each throttle body are adjusted to go on without any pretension, then attach the pull rod from the bell crank to snap on without any pretension. With the engine running pop off each rod that you just attached to ensure that it has NO effect on idle speed. ONLY then can you be sure that no linkage is effecting the throttle bodies. Which mixture screw did you adjust, idle or load? They each adjust in different directions.

[Scott Clarke]

You need to adjust your hand trottle. Attached to the hand throttle lever is a soft (like rubber) fork that bears against a stop attached to the throttle rod. This stop is attached with a set screw, and can therefore be adjusted. Also, the rubber fork is likely to be worn, deformed, or damgaged. Replacements are available new, and are reasonably priced. My hand throttle will hold the motor at redline if I choose. Note that the factory starting and cold running procedure requires the use of the hand throttle.

[Gary R]

Hi Ed & Scott,

Sorry it took so long to get back to the both of you. I thought I was signed up to get automatic e-mail notification, but I must have done something wrong.

Ed-

I remembered your advice about disconnecting the linkage (from an earlier thread), so that there is no pre-tension. I did as you suggested, but this had no effect on the idle issues described above. The pump control rod was set by a fixture at Eurometrex at 114MM. I checked it with my calipers and it appears to be right on. I set the timing to 2 degrees ATDC at idle. I will recheck it. The mixture screw I adjusted is the one that you adjust by going thru the fan and shroud with the hex head special tool. I believe that to be the idle speed adjustment screw. Is that correct?

Scott-

I will look at my hand throttle, and check to see the condition of the "stop" and try to adjust it. So what I am gathering from you is that if my idle is around 950 RPMs when the car comes up to temperature, I was on the correct track with the pump being set too lean. Or are you just helping me with my throttle level issue and not giving an opinion on what I was experiencing with the car idling too high when fully warmed up.

Scott do I get that rubber fork through Pelican or do I have to go through a Porsche dealership?

Thank you both for the input you have given. Any further support is greatly appreciated.

Sincererly,

Gary

[Scott Clarke]

Gary-
It seems possible that, if you have achieved a 950 rpm idle with a reasonable mixture, then your only remaining problem is the hand trottle. If everything in the injection system is perfect, the car will operate just as you describe with the hand throttle all the way down: idle too low when cold. The factory prescribed cold start and running procedure is to pull the hand throttle lever all the way up, crank until car starts, and then adjust the lever until the car is idling at 1500 rpm. Then, as the car warms, continue to adjust the lever to maintain a 1500 rpm idle. When sufficiently warm, push the lever all the way down to achieve the warm idle spec. If you are not able to radically change the idle speed with the hand throttle, then something isn't working. I can use mine like a dangerous version of cruise control. I can set it to maintain 75mph in 5th gear (not that I condone such practices!).

You might want to find someone with a CO meter to verify that your idle mixture is about right. It would be a shame to be controlling your idle speed by means of an excessively rich mixture, instead of addresssing some other problem. That said, your theory about the mixture being initially too lean seems plausible.

Pelican can get the part, I'm sure. I think I might have gotten mine from Stoddard's.

[Gary R]

Hi Scott,

Thanks for the input. I will get a CO meter and check it as well. I really appreciate your input. I will post later this week or early next week what I found out.

Gary

[edmayo]

Hi Gary, yes, the idle adjustment is what you're doing through the fan, and yes on the idle adjustment clockwise is rich. It is just the opposite on the load adjustment. You need to follow this procedure; Run engine until 180 temp is reached, timing must be correct, the thermostat housing must be HOT, the load adjustment MUST be done first. This will require some means of reading the mixture while driving (it's possible to get pretty close by feel, but that requires a lot of experience) Remember, the load adjustment affects the whole range, but the idle adjustment affects ONLY the idle, that's why it is done last. ONLY after the mixtures are correct do you adjust the idle speed with the air stack by-pass screws. If after all this you aren't able to get the idle down then you need to, with engine running, disconnect every linkage rod one at a time, to see if it changes anything, reconnect it, and go to the next one. And I mean each rod to each individual butterfly also. There should be no reason with new Eurometrix throttle bodies that you can't get the idle low enough. To make sure your hand throttle or other linkage isn't sticking or on, disconnect the pull rod from the bell crank (back by the #3 cylinder) from the cross bar. There must be NO outside influence on the throttle body system. I don't even use the hand throttle for starting. AFTER the engine is running I'll pull it up to keep the engine from dieing the first five minutes of driving. Most of the time I don't even use it. Do not expect a perfect 950 idle speed on a cold MFI engine, it doesn't happen! Let me know how this goes.

[Gary R]

Ed-

Thank you for being so considerate to take the time to help explain what I need to do to get my car to run the way it is suppose to. I am determined to learn how to completely tune my 911E and with the help from people like you and Scott, I believe I can get there.

My next step is to check out my hand throttle get it in perfect working order, then I will rent a CO meter and check the load richness. I will keep you posted, but it may be few weeks, because my wife has many spring 'honey do's' for me as well.

Talk with you soon and thanks again for your consideration and effort.

Cordially,

Gary