328 warm-up idle

There's a dozen components involved with a cold engine such as the cold start injector, thermo-time switch and some relays in the ECU, a WUR (warm up regulator) which alters fuel pressure when cold. But the primary device controlling rpm increase is the vacuum solenoid oft called an electrovalve.

Action starts at the switch at the bottom of the coolant overflow tank which shorts to ground, energizing some ECU relays and applying voltage to that electrovalve.

The switch shorts to ground when the engine is hot. So start the engine, unplug the connector to that switch. If rpm's are still unchanged, replace the connector and turn your attention to the aforementioned electrovalve, which controls vacuum flow.

Engine speed should increase when additional vacuum is 'spilled' into the plenum atop the engine. On my car I've 'rewired' the vacuum hoses to prevent the high idle rpm. Your PO may have done the same or even just unplugged the connector.

Next question you ask is "where are things"

Picture below stolen from an AWulf post has faint red arrows showing electrovalve and plumbing ( http://www.ferrarichat.com/forum/showthread.php?t=141229&highlight=electrovalve+rpm )

...Also check this thread for another electrolvalve discussion (ain't search wonderful) http://www.ferrarichat.com/forum/showthread.php?t=214546
Image Unavailable, Please Login

 

60 minute edit timer got me just when I was about to add -

The large black elbow shaped hose lets air into the beautiful red plenum above the engine, thus increasing rpm.

 

Depends on what you mean by "cold" and "higher". On your model (328), the only thing adding extra air into the intake path after cold start-up is the AAV (the device that Paul mentioned is only used on US '80-'82 308i-2V and US 1983 308QV), and, unless really cold, the RPM increase isn't a bunch. If it's below 1000 RPM, and obviously struggling to run, it might be worth removing the AAV and putting it in the refrigerator to confirm that it is opening when cold, but, otherwise, what "problem" are you trying to fix?

 

There's two things to check with the AAV , firstly, as above, put it in the fridge/freezer to see it open & then in also a low heat oven to make sure its also closing fully. Secondly make sure that the electric circuit is OK - stick a continuity tester across the two pins on the end of it, if there is no circuit then it isn't going to work properly.

Before replacing parts or going any further start checking your hoses. There are numerous air hoses in the bypass/idle system not to mention several vacuum lines including the long one that goes from the left side of the plenum back to the Ignition box hidden under the boot floor (left side). I have also been told that it is common to get air leaks around the fuel injector seals. If you have any air leaks anywhere then you are likely to have idling problems to some degree or other.

Its also worth adding that not all cars will behave the same. The two principle components in the warm up system are the AAV and the warm up regulator. Both of these use mechanical bi-metallic strips to react to heat & adjust air/fuel supply to the engine. While they are more than accurate enough, there will inevitably be a variation between how such devices work.

 

This is true for US '80-'82 308i-2V and US 1983 308QV (non-Lambda) because they have the cold start air valve system that Paul described earlier (and it is excessive ). On the later (with Lambda) cars, the cold light-off RPM isn't so high. If it's 40 deg F (and the engine has sat long enough so the whole thing is at that temperature), it might got to something like 1400~1800 RPM for a short while after light-off, but, at 75 deg F, it might only be something like 1100~1200 RPM for a short while after light-off.

Hard to say if you really have a problem here, or not, since your tach isn't working! Often people mention their idle as being set at something like 750~800 RPM when warm, which is a little lowish to me, and won't help cold-running, so I hope that you are working on getting your tach working. I don't blast off right away after cold start-up, and might manually exercise the engine up to 1500~1800 RPM a time or two before moving off, but, if you can't drive away (gently) 1/2~1 min after cold start-up you've got some other problem IMO (i.e., gentle inital driving should be your warm-up, not sitting in the garage).

 

328 documents all indicate warm idle of 1000 +- 10% rpm plus clearly refer to fast idle circuitry activating when engine is cold (commonly 1200-1500rpm). And the 328 wiring diagram clearly shows coolant switch activating the fast idle electrovalve activates the AAV through vacuum hoses which causes the fast idle rpm.

If you do want the fast idle to work, pursue troubleshooting the fast idle electrical/vacuum circuits NOT the fuel pressure circuits. You're complicating a simple problem.
Image Unavailable, Please Login

 

Can you please show or explain this? -- i.e., AFAIK, there's no electrovalve (nor cold start air valve) associated with the AAV's operation on a 328.

 

Or that something temporarily sealed itself....

See how you get on with it -if it works sometimes & other times not then I would start looking at electrical connections & air/vacuum hoses

 

I have a similar problem and looking at the schematics or any pictures I have seen leave me wondering if all the vacuum connections are hooked up correctly. Any pictures of the valve connections that anyone has would be helpful as I am replacing all the lines on the engine. Easy maintenance while I have the time. Car is an '80 308 GTBi. Seeing the earlier post about the incorrect routing makes me look at the open-ended valve and wondering if they are correct.
TIA (God, I'm using acronyms now)

 

Found this snippet in the 1988 OM (below).

I can't find any coolant tank thermo switch specs anywhere. Perhaps your mornings have been warm enough the fast idle wasn't activated. Removing the connector and artificially opening and closing the circuit may be the only way to know for sure.
Image Unavailable, Please Login