My 86 328 starts up fairly well, drives nicely, but sometimes idles very roughly when warm. It has new plugs and drives very well overall. I'm a Ferrari novice and did some searches on FChat but most threads are about rough COLD idle issues. Where should I start?
Possiblities: A. Check for false air. Probst (a book to purchase) mentions using propane gas as a sensor...(gas only, not the lit torch). If idle goes up, then tighten the false air inlet to closed (usually a hose clamp(s)). Vacuum leak=false air. B. Try temporarily disconnecting/reconnecting things during the warm, bumpy idle...see which causes a change: 1. air injection (electrovalve and water temp sensor in expansion tank)...when disconnected warm...should do nothing; 2. frequency valve (if off, unloader from control pressure goes down, giving lean condition...warm idle should bump even more)...plug back in ASAP...should come back to normal, or do nothing since enrichment duty not present at idle; should sound like a "buzzer" when operating properly; 3. WUR (also has vacuum tap for US version...false air check would reveal leak here); unplug when warm...should do nothing different; 4. Cold start injector...unplug and nothing should happen...if something does, undesired richness at all times; 5. AAV disconnecting should do nothing when warmed up; All these should take about 10 min. Wear gloves so as not to get burned. Unexpected changes mean that something's likely out of order. If any of these causes a change (save the frequency valve, which might), inspect the safety relay and fuse on the emissions ECU (do a search on this), and learn more about this system. There's a lot of interconnections between all these components and the ECU; each affects the operation. C. I'm not ruling out exhaust leak(s), but usually, an engine warmed improves problems with exhaust leakage. D. Last check, timing/ignition. Plugs may have been incorrect, or connections need improving. I also don't rule out wire misplacement, but that means two or more plugs fire out of sequence; I don't think that would be sensed as proper engine performance at any RPM though. One plug could be disconnected, or poorly seated, which may be masked at higher RPM while being more of a noticible interference at idle. Also, please keep us up-to-date. We like to figure these things out.
Rob, this is exactly what I need - a list of items to verify for functionality. As an additional piece of information, if I let the car stumble for long enough, it SLOWLY smooths out. It almost seems like there is a valve that is sticking or slow to actuate. "Back in the Day", on my old Volvo it was an ISC valve. On my 68 Mustang, it was solved with a few shots of Chem Tool down the carb throat. I'm tempted to spray carb cleaner into every orifice, but I guess I'm not in Kansas anymore.
Maybe the metering flap is sticking and not returning to rest position properly? Easy to check by pressing down on it and releasing.
This could be correct (good call, Andy). The fast idle at cold may mask a small "stick" in the air sensor plate or the CIS plunger. Also, since the fuel control pressre is always trying to place the plunger in proper position, it could mitigate over time as you cailmed. Try observing with the air cleaner filter assembly off..watch the sensor plate while at idle (cold through warm up). If it jumps, it could be sticking. Also check the throttle cable and switch operation as well.
I had the same problem and after checking everything I installed a WBO2 sensor and it solved the problem. A normal O2 sensor would have worked but I was installing a WBO2 on the 928 and thought I would try it on the 328 just to see what it would do.
So I take off the air box and I imagine that I'll see a round plate of some kind - you can tell I have not gotten very deep into this car yet... If it is sticking, what should I do to clean it? Carb cleaner or ? I'll try it tonight.
The plate rests against an endstop and when pressed down and released it should return to the stop. But this does not necessarily mean the piston is returning fully. Without fuel pressure the piston returns relatively slowly. If you let the plate return back up, then press down on it slightly again immediately, you might find there is a small amount of play before it hits some resistance as it moves the piston as it has not fully returned yet. If there is still play after a time though, the piston is sticking. Another test you could do is with the engine running. If you get the engine to run normally, without the fault present, then press down on the plate very slightly, it will falter and almost stall as it will be very rich. Then let the plate back up, and it should return to normal running. If it does not, the piston could be sticking.
A quick fix is to check all the low voltage connectors in the engine compartment. Especially the connectors of the ignition modules and the main connector situated near the expansion tank, under the left fender. Pull them and lube them up with contact-spray.
