Help! Another hunting idle Carrera issue
 

Hi all
I am at my wit's end with this.
I have a 1985 3.2 Carrera engine transplanted into a 1979 body.
During the transplant process I tried to proactively deal with any maintenance issues by replacing the following:
1. Idle control valve
2. Speed sensor
3. Reference sensor
4. Cylinder head temp sensor
5. Spark plugs
6. Fuel pump
7. Fuel filter
8. Fuel tank
9. Fuel lines to and from the engine, including the lines on the engine
10. Ignition rotor
11. all vacuum hoses
12. DME relay
13. DME was checked and re-soldered by Ingo Schmidt
14. New headers and exhaust from RarlyL8

There are probably other things as well.

Other than the headers the engine is completely stock.

I've never had the engine running (properly) - I bought it used.

The engine fires up immediately, but idle starts hunting immediately. According to my Innovate LM-1 wide band sensor, air/fuel ratio is very lean - 18 or 19.

After about 2 minutes idle settles down, and air/fuel goes to normal - 14.2 or so.

After another 3-4 minutes the mixture leans out again to 18 or 19.

If I rev the engine to 2,000 or so, mixture returns to 14 or so.

I've done a fuel pressure check and according to my gauge both the system pressure and running pressure are about 10% high - I would have thought this would cause it to run rich if anything?.

I've checked all the sensors with a multi-meter and all are within spec, including the speed and reference sensors, the idle control valve and the cylinder head temperature sensor both cold and warm.

I opened up the AFM and tried adjusting the sensor tracks - no change. I tried adjusting the clock spring and although this helped the idle mixture, it made the mixture too rich at higher rpms.

I've run it with the O2 sensor connected and disconnected - no change.

I've done a smoke test and there are no leaks.

I re-torqued the intake manifold bolts.

I'm trying to understand what input would cause the lean idle mixture? I'm embarrassed to drive the car the way it is running now, not to mention that I can't see that is would be good for the engine to idle so lean.

I know this issue is similar to Wayne's thread, but it doesn't seem like he has his issue resolved either

Oh no - have I stumped the experts?

one more time Anyone?

Have you cleaned and flow tested the injectors? I don't see distributor cap on your list. Also, what kind of spark plugs did you use?

ok all this i do not see what is your mixture on the scale not the 18-19 i am an oldtimer mechanic so i`d like to see what is the C/O in % on the testing machine...
i`m saying this i have never used one of this testers(wide band or other) ,no needed to, to set up the engine to run properly...

Ivan

I went through this same symptom...checked everything possible, and it was ONLY fixed by going to a MAF system (from Sal Carceler who is on PELICAN) which removes the stock AFM box, so it makes sense - at least to me - that that was the culprit. Unlike the MAF, the AFM has lots of moving parts and with age and mileage things can go wrong. I have no experience is taking one of those apart and or whether a problem inside it would be obvious.

Did you replace the intake manifold gaskets while the engine was out? It is very common to see idle issues with these as the intake gaskets age and start to leak. the 3.2 has a stacked gasket set with a spacer in between.

Thanks for all the replies. Pedro - I had the injectors cleaned when I first started my project (that is about 5 years ago, but I only got the car running this summer). I also replaced the cap. The plugs are new and are the factory recommended heat range.
Proporsche - I don't have access to a testing machine that reads out in C/O, but it is most certainly running lean - 14.7 is the ideal mixture at idle.
73pcar - I am hoping to find someone local who has a Carrera so that I can swap out the AFM and DME just to eliminate those. I will post if I am successful at that.
76fj55 - I did replace the intake manifold gaskets. The spacers were in good shape and I have re-torqued the intake manifold bolts. Plus, I sprayed starting fluid around the manifold runners to see if it changed the idle - no difference.

Thanks again to everyone - any other theories?

Is the throttle-body clean?

Confirmed that there are no vacuum leaks?

Is the restrictor in the main vent hose?

Has the idle bypass been messed with?

RR

Hi Soyracer
Throttle body is clean - I dismantled it and cleaned everything inside. The restrictor is in the main vent hose. Idle control valve has not been messed with, but is new and I have confirmed that it opens and closes as it should.

i would just lean it....

Ivan

But it is too lean...

Age and condition of O2 sensor?
When it warms up the sensor will control AFR running and at idle. During warmup it is in closed loop no control, also when disconnected it wil be the closed loop map.

no need for oxy sensor at all disconnect it..
i drive my 911 for 24 years without only if i have to smog it. i will connect it. Also have checked the setting on you computer? And do you have the correct computer for 1985 set up?

Run the idle bypass screw in a half turn at a time till the surging stops (the one on the throttle-body with the yellow cap on it)

RR

this idle adjustment is basically the 1st you should be dealing with before you get any technical testing about it...
http://forums.pelicanparts.com/uploa...1602175432.jpg
http://forums.pelicanparts.com/uploa...1602175432.jpg
http://forums.pelicanparts.com/uploa...1602175432.jpg

Might sound a bit simple, but have you opend up the ECU and checked if it still has the original chip fitted ?
A...

the chip would not do anything like this...i do agree ,sounds like a simple solution;-)
Ivan

Any update on this one from OP? What was outcome?

there is also a bypass on the AFM to set the idle mixture. it is capped from the factory, but that can be easily removed. have you adjusted the idle mixture at the AFM?