Idle is rock solid but high ~1k rpm.

Idle switch electricaly tested good, ISV electricaly tested good, new air filter, new fuel pump, new LH, intake r&r a few seasons ago, MAF is a JDS rebuild, vacuum lines and connectors replaced with intake project.

Fuel is fresh this spring but the tank did have stabilizer added for the winter.

appreciate thoughts

 

Same issue. Idles normal when cold then around 1,000 to 1,100 rpms when warm. I just started and intake refresh and already found possible vacuum leaks. I'll be keeping an eye on this thread to see if anyone has any advice.

 

If the O2 loop is good then it has to be an air leak.

 

Malcolm,

+1 for John's advice.

No idle speed adjustment was installed from MY1987, as the idle positioner takes care of the idle speed adjustments.

This idle positioner has a hose from infront of the IP and is connected behind the throttle valve, as you know. The IP receives timed ground pulses of 100 Hz via an electric wire to the control unit. Engine speed, engine temperature and equipment such as air conditioner or automatic transmission are transferred to a speed cure and compared wiht the actual speed curve in the control unit.

In view of the work that you have carried out in this area I would check all your connections for an air leak. You may need to undertake the "olde" blow smoke into the inlet and check for leaks or you can pressurise the inlet system by making a closing off connection to fit over the MAF inlet, fitted with a tubeless tyre valve and a pressure gauge and pressurise the system and then check for leaks.

Porsche uses a flat circular plate, rubber backed fitted with the tyre valve and pressure gauge. This is connected to the MAF by 2 long screws and nuts.

There is a post on RL where a rubber reducer has been used and the largest diameter secured to the MAF inlet by a jublee clip and the smaller diameter is fitted closing cap, again secured by a jublee clip and fitted with the tubeless tyre valve and pressure gauge.

When you have found the leak carry out at 'adaptive' procedure via a diagnostic tool or drive the car until it self-adapts to the current conditions of your car when it is up to operating temperature and it should set the idle speed correctly.

Tails 1990 928 S4 Auto

 

O2 sensor was replaced with the x exhaust but will double check.

I saw Dwaynes intake project thread that included pressurizing the intake for leak checks...........I could go that route

 

Look at the 2 plastic junctions that plug into the MAF boot they are thin and frequently snap, crackle

 

thx Stan.........hate problems in the spring of our very short season.

 

Today I swapped out the spark plugs...........I had the Bosch quads in there for the past 7 yrs but when Colin provided the rebuilt LH and PEMs for both brains he suggested that I had an ignition miss on restart. New plugs are the OEM copper type.

The new plugs provided SITP more smooth power but didnt affect the high idle despite the fact that 6 of the 8 old plugs were not what I would consider tight..............I generaly torque the spark plugs.

Back to square 1.

 

How were the plugs?

 

Nice brown/grey colour............all consistent............no damage.

The miss that you heard with the old plugs was when the engine was cold............it smoothed out when the engine warmed.

Engine was cool but not overnight cold after the plug swap. Can't look for a while..............220 gets the lump on the warm side.

I don't want to take the intake off.............again

 

It might be worth a (second) look at the throttle body to quadrant cable adjustment .... a bit snug could play tricks with the IPS.

To chase down an air leak, use a propane torch .... unlit, BTW .

 

Backed the cable off and no change.

Thought of the torch solution many times ...........too much time and $$$ now.......good to hear from you Garth.

 

Malcolm, didn't you just finish an intake job? Did you paint or powder-coat the water bridge?

 

Dave.........yes, intake r&r 2 yrs ago............all hoses, gaskets replaced.............FIs cleaned. ISV and TPS checked good then and now.

What happened over the winter to cause this is unknown but I did have a break down (seperate thread) and since have replaced the OEM fuel pump and LH with PEMs in both brains. PEMs are basic maps and need tuned.

Hi idle issue existed before the above changes this year............not before winter shutdown.

If there's a RAT somewhere it'll get the 12 guage solution............followed by 22 target practice and 284 blown to hell...........I love living in the country till it screws with the 928.

 

Hmmm... how did you test the ISV electrically?