Still can't fix my cold idle hunting/surging!

[kamaro]

I'm fighting that nasty idle surge/hunt since I transplanted a RoW 3.2 carrera engine (no O2 sensor) into my '77, its ONLY occuring when dead cold, and sometimes its enough to blip the gas pedal a few times to get it cleared out. These are the things that I did so far :

- Completely eliminated any chance of a vacuum leak, re-sealed EVERYTHING, from the intake manifold gaskets and spacers to re-sealing the injectors, replacing all the rubbers, hoses .. etc.
- New set of spark plugs, new spark wires, rotor, and cap.
- Removed all the fuel injectors and sent them to be checked/cleaned.
- Gone through all the DME connections and made sure everything single wire is good by checking it with a multimeter.
- Checked the resistance of the CHT sensor, it was working as it should with all the correct values.
- Checked all the engine sensors and all of them came up with the correct value.
- Calibrated the AFM to get a AFR of about 14:1 at idle.
- Replaced the DME relay with a genuine new one.
- Checked the fuel pressure at the rail, right on the spot with and winout the regulators.
- Checked the ICV (idle control valve), working as it should, then cleaned it out real well, sprayed in some WD40 for smooth action.
- Tried to calibrate the ICV as per Bentley's manual, noticed that if I drop the idle down past 900 rpm the engine would hunt/surge so severly and die, so I kept it at about 950 rpm at idle.

As soon as the car gets into temp, it idles so smoothly (but at a higher idle speed as mentioned, at about 950 rpm), and drives great with no issues what so ever, pulling strong, no more idle surge, and cruises like a dream.

Its just seems like it has something wrong with the cold running phase, and as soon as it warms up everything goes smooth.

Any suggestion before I pull off the motronic stuff and put in a AEM or MS3 pcm!

[Archer911]

Wondering if you ever solved your surging idle issue.
I have the same problem on my 87 and 89 Carreras.

Thanks

[stlrj]

My 87 had the same problem for years until I discovered the previous owner installed the ICV upside down (arrow pointing up).

[Archer911]

@stlrj

I'll be checking the ICV as you point out but I believe both OK as they are original to both cars.

I did think it could be the fuel pump as both are 30+ years old so I replaced one and the fuel filter. No difference.

I'm going to do the tests that kamaro did vis-a-vis the Bentley manual to see if I can solve this issue. The 87 does it for much less time before evening out. My guess it's electronic and possibly a sensor.

[RedCoupe]

Archer, did you set the idle speed via the procedure that takes the ICV put of the circuit? That's the method where you use a jumper wire between two pins of the round socket in the fuse panel on the left side of the engine compartment. If you can't set the idle speed to the 880 rpm spec, there may be a vacuum leak or debris inside of the ICV preventing it from closing.

[Archer911]

@RedCoupe

I have not gotten that far yet. I need to time each car (just to see the difference in warm-up time) as the idle, after a few minutes of engine warming, becomes smooth.

I have been through the vacuum lines and also replaced the main engine breather hoses as well as the tubing before and after the ICV.

I am also bugged by the ancient fuel injectors and fuel distributor. I have an 84 Ferrari 308GTS which ran poorly, especially on startup, until I replaced the fuel injectors and had the fuel distributor and warm-up regulator rebuilt. The car only has 45k miles vs 100K+ on both Carreras.

I expect that the ICVs, being original to each car, are a bit grimy and a potential culprit. Heading down to the garage shortly.

[nene]

My 86 had the ICV arrow pointing the wrong way, which I corrected it and it made no difference.

[stlrj]

Originally Posted by stlrj

My 87 had the same problem for years until I discovered the previous owner installed the ICV upside down (arrow pointing up).

Forgot to mention that I had to make some critical adjustments to the idle air bypass to ultimately fix the hunting. ICV adjustment is critical to eliminate hunting idle.

[Archer911]

@stlrj

Didn't know you could adjust that valve as it is controlled by the ECM.

[Nick Triesch]

Tighten down the bolts of the intake runners to about 18 foot pounds. Worked for me a few years ago. I bet several are loose. Mine were. Went back to normal idle

[Nick Triesch]

Too much air getting in causing terrible warmup.

[Archer911]

@Nick Triesch

Thanks Nick. That makes a lot of sense. I'll get to that in the morning and report back.

[Archer911]

In the meantime while checking continuity and voltages on the various AMP connectors I found one of the contact pins pushed back into the plug that goes to the volume air flow sensor.
Contact was intermittent at best and I was able to get the connector forward by pushing the wire exiting the back of the connector.

[jlex]

I think you'll solve the problem once the idle is correctly adjusted.

[Nick Triesch]

Critical adjustments are not necessary on a 3.2. If in the ballpark or even not , ECU will correct and car will run fine.

[stlrj]

Originally Posted by Nick Triesch

Critical adjustments are not necessary on a 3.2. If in the ballpark or even not , ECU will correct and car will run fine.

IVC is a mechanical device that has its limits and can only operate within those limits. Factory specs are very specific on bypass air adjustments in order for proper operation of the IVC.

[Nick Triesch]

Okay, but the high end shop that did my top end said the few adjustments on the 3.2 do very little because Motronic takes care of everything. When my car was in the shop for the work and had a very rich mixture I asked about the adjustments on ICV and throttle body and they told me that was not the problem. And they were right. My car starts and idles fine now without messing with the adjustments.,

[stlrj]

Originally Posted by Nick Triesch

Okay, but the high end shop that did my top end said the few adjustments on the 3.2 do very little because Motronic takes care of everything. When my car was in the shop for the work and had a very rich mixture I asked about the adjustments on ICV and throttle body and they told me that was not the problem. And they were right. My car starts and idles fine now without messing with the adjustments.,

No reflection on you, but they apparently did not read the manual.

[Nick Triesch]

All I am saying is that if the settings are anywhere near, car will run fine. Other’s on this site will agree with me. If car is tuned up with no vacuum leaks, those adjustments do little . Motronic will get it in there.

[Nick Triesch]

Porsche says to use 10/60 synthetic motor oil in our 3.2’s. How many use that?