Fix for high idle on 400i?

I would just turn those big fat knobs on the sides of the intakes until I get the right idle speed. No tools required. Then I would fine tune the mixture screws. A 3 mm Allen key is needed for this. On my '83 400i I have tuned the mixture by giving the screw big turns, a half turn or more, back and forth, to zero in on the sweet spot. Then driveability will tell you if you've got it too lean. It will stumble on acceleration when too lean. Smelling the exhaust, and rough idle, will tell you if it's too rich. Others on this board might criticize my shade tree methods. The correct method is a five-gas analyzer. But they cost $3000 and up, while my nose is free.

 

I'm on the road & don't have my WSM handy, so all of this is from memory. For starters, you really should get the Work Shop Manual. Also, a good working knowledge of the fuel injection side of things is a must!!

WSM in pdf for about $36:
http://www.maranello-literature.com/maranello-literature/product_info.php?products_id=3600

WSM in print:
http://www.ebay.com/itm/like/111340312102?lpid=82

A good primer on Bosch K-Jet by Charles O. Probst:
Bosch Fuel Injection and Engine Management: How to Understand, Service and Modify: C Probst: 9780837603001: Amazon.com: Books

Verification that things are up to spec. with regard to fuel pressures/pumps, accumulators, filters, etc..
Ferrari 400 - K jetronic Fuel pressure meter or similar.

A couple of Vacuum gauges are also required:
Ferrari 400 - K jetronic Vacuum meter or similar.
Both are connected simultaneously to the vacuum line between the WUR (Warm-Up Regulator) and the Air Intake elbow on the exhaust valve cover on each bank.

A simple 1 gas analyzer (Carbon Monoxide):
Gunson Digital Gas Tester | eBay

& it's instructions:
http://gunson.co.uk/items/pdf/Products/G4125_booklet.pdf
CO is the only gas you can measure/adjust on these simple mechanical FI systems. Ideally, it would be best to have 2 of them so that both sides can be measured simultaneously as it can take a minute or two for these analyzers to render correct %'s after inserting the sensors up the tailpipe. But if you're patient, you can use just one (switch back & forth from side to side) but 'be sure' to let it settle down to give an accurate reading.


Again, all of this is by memory so verify all entries with the WSM:

Verify control pressures are up to snuff.
Connect vacuum gauges & set up the gas analyzer(s).
By default, those big fat screws on the Air Intake elbow are supposed to be fully screwed in. {Verify}
They're only to be adjusted to fine tune things in the end, if needed.
Check your gas analyzers for the CO content in the exhaust. The WSM states a range of 1.0%-2.0%. I feel that 2.0% is too high for these & I think carbon build-up on the heads & piston tops could result at this level. I like to keep closer to the 1% side of things but be careful not to go too lean as this could possibly result in burning holes through your pistons (rendering the need for a full engine rebuild ). The CO output can be adjusted with a 3mm T-handle allen wrench through the small vertical tube on the back side of the Fuel Metering Device (distributor). Clockwise will make the mixture richer, run cooler, & eat more fuel (& carbon-up those cylinders ). Counterclockwise will lean her out, run hotter, and yield better fuel economy. I always like to back the screws off (counterclockwise), then bring it up to the level I want. Currently, I'm running @ 1.5% with engine oil temps running a peg or 2 under 100c & H2O temps a peg or 2 below 90c (even @ speed) so I can definitely bring her down some more.

Then follow the factory procedure to adjust the idle & balance the banks, which I believe goes (for your situation):

Verify that the vacuum gauges are reading identical to each other. If not, adjust the small idle linkage screw near the base on the front side of the Air Intake elbow on one of the banks to bring it to the same level as the other bank. Then back the small idle screw on both sides to obtain your desired idle RPM while maintaining identical readings on the gauges (I like mine at 800, the WSM states 800-1000RPM). Fine tune the fat screws, if necessary, to bring things home.

Anyone see that I made any wrongful entries, please speak up

 

In the Bahamas, they call themselves bush mechanics

 

Brian
There are idle sop screws on each bank. That is the primary adjustment.

The two large screws Bill mentioned should generally be full closed. They are to balance banks if all else fails.

You really need two matched vacuum gauges to get the two banks equal. Check banks at idle and at say 2500 RPM, no load to get vacuum equal on both banks. Since it runs smooth I do not expect the main central linkage will need adjustment. Only work on it if the high RPM vacuums do not match.

Its easy and I love doing it!
Ken

 

No problem Brian, anytime!

Lol, too funny

 

So….
How's the idle doing??

 

Good deal! How close was the vacuum balance of each side??