'86 - 328 Surging at Idle

Although it could be various issues, a vacuum leak is the usual suspect. I'd start there, checking all relevant hoses/connections.

 

Can you post a video? It would really help to hear it. Usually the exhaust "blat" at idle will give some clues.

 

Easy to check: Have a look at your floor mat and make sure it isn't actually resting on the accelerator pedal. Yes, this has happened!

 

The O2 sensor is measuring the exhaust and feeding information back to the computer that then alters the fuel mixture. A very, very slight surging at idle is normal, as the the speed of adjustment in the system is not instant.

The vacuum leak can be a source of surging, as it creates too lean a mixture, and the computer is trying to accomodate but can not handle way out of range adjustments.

For vacuum leaks, tighten the clamps on the various air injection hoses, after the car is warm. They will liklely tighten more than you would expect, they are tough old hoses. Snug up the throttle body attachment nuts, and the big air intake hose clamps on the plennum to throttle body hose. Check that accordian hose for splits, might take it off to inspect it. There are a couple of small vacuum hoses, that go the an air injection electrovalve, and the ECU itself. All worth checking for integrity.

If there is no obvious vacuum leak, it would be useful to have your car emission tested, and make sure the mixture screw is set correctly in the first instance. You might be at a too lean setting.

 

That EXACT symptom can be corrected on a QV by simply disconnecting the O2 sensor.

 

None for a QV.

Mine was disconnected when I bought it in 1997. About five years later I put a new one in and it started this surging ****. I actually pulled over and disconnected it on the way to work. Again, that was around 2002.

So 25 years, 70,000 plus miles including a ton of hard track time - no problems without it.

Can't speak for a 328. I don't know if there is something different with the ignition programs and an O2 sensor, but a QV will continue long term without harm. I have proven that without question.

 

Based on my experience of owning a 328 since 2008, it doesn't surge at idle with the O2 sensor connected if everything is working properly. So IF disconnecting the sensor stops the surging, the problem wasn't fixed, just disguised.

FWIW, I always fall back on one question with many of these "problems" that are fixed in some odd way - "Did the car do [whatever the problem is] when it was new?" The answer is always, "No." People didn't take their new 3x8's into the dealer to get the O2 sensors disconnected because of surging, the cooling systems bled every few weeks, etc...

 

Cat deletion would have nothing to do with surging, if anything, your car will run better and cooler in the motor compartment.

Big G

 

I agree but I'm not going to spend 4 figures chasing down a subtle issue on a 40 year old car when I can unplug it for free and go like that for literally decades.

I tried finding it twenty years ago.

 

They apparently did surge ever so slightly when new, that was the nature of the Bosch technology at the time, mostly to get emissions low at idle as the goal. The surge will be barely perceptible if everything is in order, but it is there, especially once you understand what the system is actually doing.

I would need to hear the video of the idle to see if it is normal or not.

 

I could handle the idle "surge" but what drove me nuts was the adjustments it was making when I was driving. It felt like I was just barely tapping the brakes sometimes. Not often but enough that I couldn't deal with it.

 

The O2 sensor mounts in the cat. I presume there is a "test pipe" instead of the cat, but with an O2 sensor bung in it. You might want to bolt onb a Fabspeed cat to take down the noise (and restore the emissions). https://www.fabspeed.com/ferrari-328-sport-catalytic-converters-1986-1989/ Might still be noisy depending on the muffler you have, post a pic if you can.

As long as you actually have an O2 sensor, the cat and muffler changes should not have any effect on idle.

I am not a fan of the chrome elbow, the engine moves around quite a bit, and the OEM accordian pipe (part number 118310) is designed for that. That said, there are some others that have the elbow like yours and I don't recall anyone reporting a problem. Those are silicone hoses on the elbow and can be tough to keep snug, so definitely tighten those up.

 

I recall hearing of an issue someone had with one of the hard elbows, but don't remember if it was surging. Certainly if the elbow has a leak, that will draw unmetered air into the engine and definitely mess up the fuel/air mixture. Anything like that happening after the K-jet metering unit will cause a double-whammy, since it leans out the mixture and may create a feedback loop. So I can see how it could lead to surging.

The O2 sensor drives the frequency valve to provide fine adjustment of the fuel pressure on these K-jet Lambda systems. I am pretty sure one can override this feature in a couple different ways and turn the system into a more traditional K-jet (no "Lambda"). I've never looked into it, but it could be helpful in some scenarios. There is a rudimentary ECU in there too, and those can over-complicate things beyond just disconnecting a sensor.

 

"I am not a fan of the chrome elbow, the engine moves around quite a bit, and the OEM accordian pipe (part number 118310) is designed for that."

I agree! I bought one of those shortly after buying my 328 in '08 but removed it/reinstalled the OEM hose a couple of years later for exactly the reason you mentioned. The chrome pipe came with some flexible hose connectors to allow flexing but I decided that having the "flex" available in the entire length of hose rather than an inch or so at either end was a superior system.

That being said, I CANNOT say that I observed any problem with the chrome pipe!

 

My 86 328 did surge a bit, you could hear it and see it on the Tach just a 100 revs or so. my QV 308 did it more and it was much more noticeable while driving. Unplugging the O2 sensor is the way to go. essentially the combo of the modern gas, and the CO measurement means the car has to go up and down much more in its idle to correct the CO. there is likely nothing wrong.... but what has moved on is the fuels, and that is what would be causing the hunting. A 328 no longer has to meet emissions ( outside of Ca. I think ? ) so it will run better and give you slightly more performance - the normal/ static stoichiometric runs the car a bit rich. so you may notice less fuel mileage, but also less heat as the car runs less lean than before. the other thing to check is the protection relays and fuses in the bottom of the trunk on the right side. a loose connection can magnify the issue. Also an air leak under the Aux air valve ( under the catch tank ) can cause more hunting than normal until it warms up... if there is a cracked hose it will get worse as the car heats up..... I changes all the air hoses on my 328 - and wow, it was so smooth... they get brittle from the inside out - and start to let in air etc.. can drive you crazy.

 

FWIW, I have a hard intake tube as well (carbon, not metal.)

I did have an issue at some point with unmetered air due to a hose clamp I'd left loose, but after tightening it was resolved. I've had zero problems with the tube itself, instead of using the OEM.

 

I had the same problem mine was the TBS Switch (black box on the side of the trottle body) it was moving from 7-40 ohm in the idle position it should be always below 10 at idle it went from 1000-1800 up and down.very easy fix new switch $70.00 2 screws and slide the new one on and adjust the switch. You can find the adjustment in the search forums

 

I had not thought of the different gas now vs gas in 1984.

 

where did you get the new switch?

 

Isn’t it a TPS? Throttle position sensor?

https://mofler.com/uploads/attachments/monthly_2015_09/Ferrari_328_TPS_pdf.7a73439afcc9849e1f26c84844015637

 

You are misreading the title of that article -- it correctly calls it a "Throttle Position SWITCH" (which is also, unfortunately, abbreviated "TPS").