Noticing a rough idle with higher RPMs?

ANDREWMOOREFIELD

MEMBER
1990 FERRARI 348TS
3.4L
V8
2WD
MANUAL
64,000 MILES

Started noticing a rough idle with higher RPMs and sometimes the engine would act like it wanted to stall while parked in neutral. Went on a drive and when I would come to a stop and engage the clutch/shift into neutral while stopped, the RPMs would shoot up sometimes as high as 5,000 as if I was revving the engine but it was doing that on its own. Next, the Slow Down 5/8 light came on and went off twice indicating the cats were beginning to overheat on the driver's side of the engine bank but the light went off.

When I got the vehicle back home, I went to clean the MAF sensors and the throttle body’s. While doing so, I found an oily sludge in the air intake on the driver's side between the MAF sensor and the throttle body.

What could be causing this?

3 Replies

KEN L

MASTER CERTIFIED MECHANIC
47,643 POSTS

So, if the driver side catalytic converter is starting to plug it can cause all of these issues because it will cause excessive pressure inside the engine which will force oil into the intake system and make the engine idle rough. I would remove the cat for inspection. Also, remove the spark plug to make sure then all looks the same, which can indicate a problem with one or more cylinders which can help us figure out what's going on as well. The car has 64,000 on it, correct?

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Thursday, September 26th, 2024 AT 3:36 PM

ANDREWMOOREFIELD

MEMBER
3 POSTS

Thank you for the reply! Yes, the car has 64,000 miles. I was able to get the diagnostic codes pulled but I can’t find any about what they mean in my manual. Here is what I found:

Drivers side, engine cylinders 5-8
1211
4112
4122
4121
4114

Passenger side, engine cylinders 1-4
4121

Any idea what these codes mean?

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Thursday, September 26th, 2024 AT 4:17 PM

KEN L

MASTER CERTIFIED MECHANIC
47,643 POSTS

Well, you have some problems here, did all of these codes come up at once? If so, I would think the ECU is bad or you have a bad ground.

1211: This code indicates a fault in the Throttle Potentiometer.
4112: This code points to a problem with the Air Mass Meter (MAF).
4122: This code usually signals a problem with the Lambda (Oxygen) sensor 2.
4121: This code refers to a fault with Lambda (Oxygen) sensor 1.
4114: This code indicates an issue with the coolant temperature sensor.

Let's check these sensors out to see if they are connected and if so, I would clear the codes and start the engine to see which ones come back first. Please let me know.

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Friday, September 27th, 2024 AT 10:44 AM

Noticing a rough idle with higher RPMs?

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