Help: Running too lean and idle speed

[jkyook]

Hi everyone,

Since I am going stay in Korea sometime, I brought my 1989 930 to S. Korea and went for required ‘New Car Evaluation’. Unfortunately, my car failed in two items.

1. Idle speed is varying with the engine temperature. For cold start, idle is around 800 but it goes up to 1100 with hot engine. The Korean law requires that the idle speed stays between 600 and 1000.
2. Lamda is between 1.26 and 1.41. The law requires that it should be between 0.9 and 1.1.

My car passed the Smoke Check in California. Thus, I didn’t worry much for the required test. Now, I cannot register my car due to above two issues. Without it, I cannot drive my car.

What would be easy (or hard) solution (if exist) or what should I do?

Thank you for your time.

PS: I have to buy parts from the USA and fix it at here, S. Korea. Thus, I should buy extra items although it may not be the fault item due to long delivery time.

John

[dos531]

If those readings are just at idle its very easy to adjust. There's an allen key on the fuel distributor for idle mixture, and a flathead screw on the throttle body for idle speed if I recall correctly.

[jkyook]

Originally Posted by dos531

If those readings are just at idle its very easy to adjust. There's an allen key on the fuel distributor for idle mixture, and a flathead screw on the throttle body for idle speed if I recall correctly.

Thank you for your input. Is it too lean to adjust using the screw on the fuel distributor? I never done it before so I am not sure how much we can adjust using the screw.

[Bucketlist]

Have you had this car long? Is the car stock or modified? Do you have an adjustable WUR? Do you have any way to check your control pressures or monitor A/F ratio (lambda)? Is there anyone there that can work on this car for you that might have the required knowledge and tools?

If this were in my garage in the USA I would start by lowering the control pressure by adjusting the warm up regulator, this would help to bring the lambda in line while monitoring the air fuel mixture. If the idle was still high I would adjust the idle adjustment screw on the throttle body.
Good Luck!

[jkyook]

Originally Posted by Bucketlist

Have you had this car long? Is the car stock or modified? Do you have an adjustable WUR? Do you have any way to check your control pressures or monitor A/F ratio (lambda)? Is there anyone there that can work on this car for you that might have the required knowledge and tools?

If this were in my garage in the USA I would start by lowering the control pressure by adjusting the warm up regulator, this would help to bring the lambda in line while monitoring the air fuel mixture. If the idle was still high I would adjust the idle adjustment screw on the throttle body.
Good Luck!

Thank you for your advice. I had the car since 2010 and didn’t have any issues with the smog check. The car is almost stock car except for Andial fuel enrichment installed. Thus, my WUR is not adjustable. I can go to a local shop to monitor lamda. Unfortunately, I could not find any mechanic familiar with my car yet.

When you say ‘control pressure’, would you explain more about it? Which control pressure you are talking about? Since I don’t have an adjustable WUR, ‘control pressure’ is not relevant to my car?

When I search the forum, it seems that I should check the oxygen sensor and frequency valve. Also related relays. If the oxygen sensor is not working properly, disconnecting it would better?

John

[Bucketlist]

I was thinking of what I would do if I had this problem with my old hot rod so my comments may not apply. Control pressure is what controls CIS. Higher CP results in a leaner condition, lower is richer also affecting lamda or air fuel ratio. These conditions are controlled by the WUR and on yours a frequency valve connected to an 02 sensor which is suppose to keep this in line. I don't know what effect the Andial fuel enrichment would have. Maybe one of these guys more familiar with a system like yours will chime in and try to help you out.
Good Luck!

[mark houghton]

Your Andial is old school to enrich the mixture when on boost, thus has no bearing on idle mix. I ran with one years ago in the absence of an adjustable WUR....it worked fine for what it was made to do.

I don't understand what those lambda numbers relate to. Is it voltage as generated by the 02 sensor, or something to do with the duty cycle of the frequency valve? Just a foreign number to me. Perhaps a new 02 sensor is in order...perhaps not.

Adjusting idle mixture is easy, as is the idle speed - as already described. As to high idle as the engine warms, just turning the idle set screw counterclockwise will drop your idle but....you may have an issue with your AAV auxillary air valve (or is it a regulator as in AAR, doesn't matter). If it's not closing sufficiently when the engine is warm it will cause high idle by allowing too much air to enter post-throttle body.

As for fuel pressures, you need the proper gauge setup to check both system and control pressures. The WUR's job is to set up and maintain proper cp's. If your system pressure is fine but cp is not, then you have no recourse to adjust with a stock WUR. Rebuild or replace.

[jkyook]

Originally Posted by Bucketlist

I was thinking of what I would do if I had this problem with my old hot rod so my comments may not apply. Control pressure is what controls CIS. Higher CP results in a leaner condition, lower is richer also affecting lamda or air fuel ratio. These conditions are controlled by the WUR and on yours a frequency valve connected to an 02 sensor which is suppose to keep this in line. I don't know what effect the Andial fuel enrichment would have. Maybe one of these guys more familiar with a system like yours will chime in and try to help you out.
Good Luck!

Thank you for your inputs. I was hoping an easy solution, which seems, doesn’t exist. Understanding and fixing my car was the one of enjoyment for me. Since I have a time for a while, I wanted to work on my car. However, the Korean Car Registration requires a environmentally properly running car that will take time. Thank you for your time.

[jkyook]

Hi Mark,

Thank you for your advice. I have really enjoyed your posting for many topics.

I was planning to understand and fix my car slowly whenever I have an extra time. Thus, I bought several books and CDs for reading before I got here including ‘Bosch fuel injection and engine management’. Unfortunately, it is not easy task to register an old foreign car at here.

I found a mechanic who is familiar with air cooled Porsches, and will talk to him to find a best route for the process. After the registration, I want to spend time to understand the car. Thanks again.

John

[T77911S]

could be the mixture is wrong at idle making it idle up once warmed and mixture is correct.
check AAV as said.
the O2 sensor does not come into operation until warm. perhaps a new one.

check for air leaks.
could be too lean at idle.
one thing you can do is push down or pull up on the sensor plate to see if changing the mixture helps at idle. i would try it cold and hot.

you should get your hot idle correct, the CIS takes care of cold idle with the AAV and richer mixture.
again, air leaks.
knowing your fuel pressures would be a great help.
if no gauges check the input screen to the WUR. make sure it is clean.

[totle]

You are probably reffering to AFR as CO.

Here is a table between CO and AFR
https://porscheentusiasten.no/technical/CO_AFR_conversion.jpg

SO you are a bit rich.

You can adjust on the fuel head to lean out just to pass the smog test.

https://rennlist.com/forums/attachments/911-turbo-930-forum/214181d1187995703-having-trouble-adjusting-the-fuel-mixture-911-turbo-air-fuel-mixture-diagram-222.jpg

[flightlead404]

Hang on a second, you say its 800 rpm COLD and when warm goes UP to 1,100 rpm?

If so, that's backwards. It s/b higher when cold maybe 1,200 rpm, then dropping to if I recall correctly 950+/- 50 rpm when warm.

There are a couple mechanisms to do this, including the aux air regulator which provides an alternate air feed bypassing the throttle plate. It uses a bimetallic strip to open/close and 12v to heat that strip. That thing is notorious for clogging. Do some searches on here for how to clean and test it. Its the squarish aluminium thing with two 1" hoses on the RHS of the intercooler. Standard Bosch electrical connector on it.

The failure mode for that thing is basically it gets stuck, possibly fully open, possibly fully closed, possibly somewhere in between, who knows you'll have to pull it and test it.

Rather than paying $ and playing "swap the parts" I think I'd start by doing the following:

1. Remove the AAR, test, clean etc. If it is not working then you should replace it but it might not be necessary for you to pass. It just means hard starting when its cold. Search this forum for details.
2. Double check all your vacuum hoses. Assuming you have all the stock emissions control stuff on there, there's a dozen hoses. Make sure all the hoses route correctly and hoses are not cracked or hardened or split in any way.
3. When the engine is all warmed up nicely, use the bleed air screw on the LHS of the throttle body to set RPM to 950 or so.
4. Use a gas tester if you can get your hands on one to set the % CO. This is the 3mm socket head screw on top of the fuel distributor. You'll have to 3 and 4 a few times as each affects the other.
5. At this point your engine is more or less adjusted for when its warm. When warm it should start easily, idle smoothly, and be more or less in line with the test requirements

But, my guess from your description is that you'll have hard cold starts unless cleaning the AAR fixes it. It sounds like someone has adjusted the way the engine idles warm to compensate for hard cold starts (maybe?)

There are some Pierburg switches (electrically switched air valves) in the mix of those vacuum hoses (gold metal boxes with wires and two hoses). At least one of those is controlled by a temperature sensor (a switch) that (again from memory) is in the RHS chain housing. Make sure those are working correctly and the temp switch operates properly. A few jumper wires, multi meter and blowing through the switch is all you need to do there. Those switches are on a million cars from the 70s and 80s so s/b easy to find cheap if one is bad.

Finally there's WUR. That's going to be the most difficult to test and the most expensive to replace, I'd check it last. Again you can find details on how to test on here, but I'd do the standard CIS pressure tests and just check that cold and warm control pressures are where they should be and that the pressure changes as per the book.

Don't go changing any pressures until you've done all the easy stuff first.

[gsxrken]

Worth snugging up each of the 13mm nuts that hold down the 6 plastic fuel injection blocks under the intake manifold, too. They loosen up over time and can cause leaks. And it’s free.