1970 911E MFI High Idle Problem

[CoreyJ]

I know much has been written on this topic but I wanted to ask what the forum comments are for our particular problem. Here's the situation: Cold start, engine starts up and idles fine at about 1,100 rpm. After being driven and warm, idle remains at 2,000 rpm, however, by just letting out the clutch a bit to put the engine under a load, it drops back down to 1,000 rpm. At the next stop light, same thing - idle only goes down to 2,000 rpm, load up the clutch and drops to 1,000 rpm. We've replaced items recently, new injectors, cap, rotor and plugs, fuel filter. Checked and set timing OK. Can't believe it's an air leak in the system because it's not a constant condition. Appreciate any help out there!

[Rot 911]

Have you checked the throttle linkage for binding? The lubricant in the ball and sockets can get old and hard. Also can bind in several other places.

[CoreyJ]

Thanks Kurt, I'll try that next. I can see someone has added two extra springs to help bring all the throttle linkages closed. We will clean and lube the ball and pivot points and check that the throttles are fully closed.

[boba]

Check the hand throttle, it may be down but in a bind. Also check the foot feed.

[dtw]

I had this exact problem and my linkage to the main rack on the MFI pump had worked itself half a turn longer. This held the throttles open at the idle stop, leaning the mixture (bad juju) and thus causing a high idle. Mine would also drop to 1krpm if I loaded the clutch.

Adjusted the rod to the correct length and all was well. Run CMA and you'll figure it out, but get on it in case your mixture is leaned out.

[BK911]

Could also be stuck advance plates in the dizzy.

[Grady Clay]

These are all good 1st steps.

What did the old sparkplugs look like?
How long since you have done a through CMA2?
What is the history of the engine? Rebuilds, modifications, recent tune-ups, storage and maintenance (oil & filters, fresh fuel)?
How has it been driven recently?

I would summarily replace the plug wires and plug connectors.


If someone has installed extra throttle springs, you should go through the entire throttle linkage in the chassis and leading up to the engine linkage cross-bar.
This would be a good time to replace the plastic bushings (with OEM plastic) at the pedal assembly, transmission bell crank and at cylinder #3 bell crank.
Replace the throttle cushion next to the transmission.
Inspect the accelerator pedal for damaged or rusty hinge.
Be sure all the ball socket links are rotationally ‘centered’ and not in a bind.

There are several good threads about servicing the hand throttle.
The white plastic link is subject to age disintegration.
The cork ‘friction-washers’ need to be inspected.

There are several plastic bushings supporting the throttle rod in the tunnel.
You can inspect these with a fiber-optic inspection camera.

Be sure to check that the throttle travel is limited by the stop on the floorboard – even when you push the accelerator pedal hard.
The floorboard must be in suitable (strong enough) condition.
Under full throttle at the pedal, the linkage at the engine should still be free to move a bit more.

Clean and lube the linkages at the MFI pump and throttle bodies ONE-AT-A-TIME, keeping them in their original positions – no not adjust these links.

Occasionally, over the years, an incorrect bell crank at the transmission could have been installed (the lengths and angle between the lever-arms vary).
Inspect that each lever ‘goes over center’ during the travel.


With the throttle link to the cross-shaft disconnected, inspect that all six butterflies are each on their individual stops and not held open by linkage.
Don’t adjust anything (yet).


A good service procedure is to set the engine at TDC compression on #1 cylinder and take the distributor out.
(Make sure there isn't some debris that can fall in the engine.)
Clean and replace whatever is necessary.
Carefully inspect your rev-limit rotor, measure the resistor (~5KΩ).
Run it in on a Sun distributor machine and confirm the advance operates correctly (doesn’t stick as noted above).
Confirm that the advance curve is correct for your engine.
Make sure your distributor clamp securly holds the distributor (can't rotate).
Install a new distributor O-ring seal.


I would not start adjusting the MFI mixture or linkage until you have recent highway miles and some ‘sporting’ driving on the engine.
Once the engine is ‘settled in’ with driving, measure the cylinder leak and cranking compression.
With acceptable measurements, check the valve clearance and cam timing.
Check the MFI pump timing. Test the injection nozzles.
Measure the exhaust mixture.
Complete the rest of CMA2.


It may turn out that the throttle bodies are worn or mal-adjusted.
There are several good threads for testing and (as a LAST procedure) adjusting.
Absolutely do not adjust the MFI until you have confirmed all the necessary pre-conditions.


I agree with the above; a likely culprit is the distributor advance sticking.
Use the opportunity to do a complete CMA2 and know everything is in good condition and properly set.
This will ‘pay off’ the next time there is an issue – you have a known ‘baseline’.

I hope this helps.

Best,
Grady

[CoreyJ]

Thanks for all your suggestions, we are going through those trials right now and I'll report back!

[Grady Clay]

Corey,

A common issue with our wonderful old geriatric MFI is to ‘get lost’ in adjustments.
This is where you find some adjustment (timing, MFI, other) improves the running.
You say “Ah Ha! We found the problem!” Not necessarily so.

A 2nd (or even 3r and 4th) mal-adjustment can seem as if a problem is improved.
The system is fooling you and you end up with several simultaneous problems.
Even experienced and skilled technical experts get fooled this way. I have.
One problem or mis-adjustment is difficult enough to solve.
Having multiple problems exponentially compounds the difficulty.

There have been situations where someone got ‘completely lost’ in adjustments and diagnosis (wrong order).
Some have had to ‘start from scratch’ rebuilding everything. A very expensive way to tune your MFI.

This is the reason for most to follow the Porsche Check, Measure, Adjust (CMA) procedure.
Critical is the Check & Measure before you Adjust.
If (when) you adjust, keep exact track of what you do.
The original CMA assumes an almost new MFI system and only one part or system needed adjustment or replacement.
With our geriatric MFI, there are more than in the original CMA, hence the “CMA2” moniker.

CMA2 isn’t written in one place.
It is scattered among the many Pelican threads.



Please answer my questions in my last post.
Those answers will direct our looking for the best solutions.

Best,
Grady

[CoreyJ]

Grady, I don't really have a lot of history on this engine, it's a 1970 911S with a 1971 911E engine. It had new plugs, wires, cap & rotor last fall, then not driven until two weeks ago from winter storage. Prior to that it had been in storage for nearly two years. It started well enough but had no power. We drained the old gas and put in fresh, changed the oil & filter, fuel filter. Found one cylinder not firing, found one plug lead had green corrosion even though new but sitting over winter. Checked all other plug leads now ok. Pulled all fuel injectors to test for spray pattern, thinking sitting for a couple years they may have gummed up, ultimately decided to replace all with new injector since no history of ever being replaced. Engine runs much stronger now.

Now the final issue is the high 2,000 rpm idle when warm. As we mentioned in earlier post, by loading up the clutch it would drop down to 1,000 rpm. Checked and lubed all ball pivots on MFI linkage and they seem OK. Someone earlier had installed extra return springs on both sides, so I think this high idle has been an issue for a while. If started and left running, starts out a 2,000 rpm and will drop on its own after 2-3 minutes. We haven't touched the length of the linkages, but with the linkages removed at idle nothing changed, will still idle high. The dizzy has been mentioned and we are thinking possibly the weights are sticking. It also looks like the rotor my have hit the inside of the cap, so we are changing out the rotor. That's the situation as of today!

[Grady Clay]

Corey,

OK … progress.

Sure sounds like the distributor advance is not returning with the lower rpm.
When you load the engine and drag the rpm down, the bit-extra spring pressure overcomes the sticking.
When idling for a while, the vibration lets the advance return.

These symptoms can also be due to the throttle butterflies ‘settling’ in worn throttle body bores.

Service the distributor correctly – take it out of the engine as I noted above.
Points gap spec is 0.3 mm (Dwell 38º±3º).
Set the timing at 29-30º BTDC @ 6000 rpm (spec is 30º). Use a good timing light.
What is your new distributor rotor rpm limited at? It is stamped on the rotor or by part number.
Redline is 6800 rpm (not the 7200 rpm on the 911S tach.)

What sparkplugs did you install? NGK BP7ES are suitable.

Do not adjust the MFI (yet).

I recommend you do the cylinder leak test and cranking compression test next.
If there is some mechanical issue, you want to know before you drive.

When you changed the oil and filter, did you inspect the sump screen and cut the oil filter apart?
It wouldn’t hurt to change the oil again. An oil change does not drain all the oil.
I trust you are using regular ‘dino’ oil. 10W30 is appropriate for this time of year.

Drain last fall’s fuel. (Put it in another car.)
Install fresh high octane (premium++ or 100 octane race) fuel and go out and drive.
The reason for high octane now is the rings are probably not sealing best yet.
This passes some oil into the combustion chamber.
This oil reduces the octane of the fuel mixture.
Without extra octane, there can be inaudible detonation.
After everything is ‘settled-in’, you should be able to use pump premium.

Run through a few tanks of gas on the highway and 'sporting' driving.
Carefully measure the fuel and oil consumption. 'Normal' would be about 12 mpg & 600 mi/qt.
Note the color of the exhaust pipe after extended driving (it should be light gray).

Hopefully you saved the old MFI injection nozzles.
Take all 12 nozzles to a diesel injection shop and have them tested.
It is not unusual for new nozzles to leak and have poor spray pattern.
You can have the nozzles cleaned in an ultrasonic tank.
Use the best six.

I suspect you will encounter a fuel flow problem from the fuel tank.
There is a fine screen filter in the tank outlet fitting.
This screen commonly gets restricted from rust and debris.
The symptom is the 911 ‘runs out of power’ and stops.
After a while (or after on a tow truck), it will restart and run for a bit.
It is prudent to drain the fuel now; remove the fitting and clean the screen. Rinse the gas tank also.
CMA has the procedure for measuring the running fuel pressure and open-circuit fuel flow volume rate.

I still think it useful (and for safety) to go through the entire throttle linkage starting at the pedal.
You don’t want it sticking at full throttle – ever.

While you are at the pedals, stick your finger under the brake master cylinder push rod.
Inspect for leaking brake fluid at the rubber bellows.
Check the brake fluid level.
911s that sit often have brake master cylinder failure.
This can be exacerbated by bleeding the brakes.
It leaks brake fluid into the pedal assembly.
A usual symptom is the brake and clutch pedals become stiff and sticky.
As soon as the reservoir runs out of fluid – suddenly NO BRAKES!

How old are the tires?


Does your 911 still have the 911S front oil cooler system?
What happened to the original 911S engine?

Best,
Grady

[boxster03]

if u have worn throttle bodies no matter how well u have the mfi/electronics /mechanicals dialed in u will idle high

[911skooter]

Just FYI

I just rebuilt my 1970 E and had a similar issue with throttle linkage..
Two problems:

1) throttle linkage rod not adjusted right (not long enough) where it goes down to the link at trans causing the linkage to hold the throttle at 2,000 ... after warmup-it would hold the left side linkage in a bind not returning to idle.

2) The plastic fork assy that connects the fast idle handle to the throttle rod (between the seats in the tunnel) cracked and bound up on the rod when it felt like it and didnt let the throttle return as well

both issues were at the same time and not real consistant..

[CoreyJ]

A few more tests....
We removed the distributor and both cleaned and re-lubed the advance plate, weights moving freely and not appearing to stick or lag. Otherwise distributor feels to be in good condition without excess play. Reinstalled, still idles at 2,000 rpms when hot, and will eventually drop down. No change when tapping the distributor, but remember it will when put under a slight load (like letting out the clutch).

To check folk's comments amount stiff or sticky linkage - without any linkages attached to the throttle bodies at all - still idles at 2,000 rpms.

Tried Unisync on intakes, right side bank drawing a little more than left, but consistent on each bank individually.

Is it possible we have some large air leak we've missed? There's no vacuum advance on this distributor, it's a mechanical advance. Timing at idle is right on, at 6,000 rpm. We had 30 degrees BTDC at 6,000 rpm. At 1,000 rpm 5 degrees and marks look right on.

Next step?

[911skooter]

ok so you have a 2k idle with ALL linkage disconnected and your unisyn shows no change between T bodies you should not have a vaccum leak. Did you disconnect the MFI linkage as well ? maybe recheck the throttle shafts to make sure you dont have excessive wear, mine has some but idles and runs ok..

[Jim727]

One more item for the mix: have you checked your throttle return springs? I've had two give up over the life of my 911. Most recently the spring just got tired and wasn't closing the intake consistently or completely.

[tobluforu]

Tighten every nut holding the stacks/butterflies, I could not beleive how loose mine were.
Did you adjust the idle screws out the proper amount of turns, then synch the stacks? Did you loosen/remove the screw which triggers the misco switch to see if this might be an issue?

[CoreyJ]

We've considered worn throttle shafts, but it does eventually drop down to 1,000 rpm if putting a load on like easing out the clutch or if it just idles long enough. It seems if it was sucking extra air in at the throttle shafts to cause higher idle - it would do so all the time (easing out the clutch wouldn't make a difference).

We keep coming back to the distributor advance weights sticking - we've cleaned and re-lubed the plates, and they appear to move quite freely, but that's all I can imagine is the advance sticking. A lot of money to send out the dizzy for rebuild just to try and see if it's the issue - shaft play is not bad at all. Again, with all throttle linkages disconnected no change. It's a puzzler!

[911skooter]

corey, took my 70E out for a quick spin yesterday and the idle was down at 950 when cold and no assist from the throttle lever..after warm up it was at 1500 and all over the board. I may not totally understand the adjustments between the throttle bodies and the MFI unit to get the correct idle speed either.. It runs like a scalded dog and doesnt miss a beat at idle or full boar but idle is up and down also..MFI engines are strange compared to carb engines for sure..what are we missing here a BIG return spring ?? engine only has 1/2 hr on it so I didnt expect perfect out of the box..

[CoreyJ]

I'll be driving the car this weekend to get some miles under its belt, fresh gas and some highway driving to clean things out a bit. As for the BIG return spring - someone has all ready installed an extra "helper" spring on each side of the engine pulling the linkages closed!