95 F355 acting up but no codes again?

Went out to start the 355 and when I started it up it stumbled a little bit and then ran a little bit rough but cleared up. After letting it warm up a little bit I drove around the block and coming to stoplights when I put the clutch in the idle would hang around 1500 to 1700 And then drop back to 1000 after a few seconds. I didn't notice a loss of power but I did notice what could be a bit of a change in the tone of the exhaust. It also smells like it's running more rich but I do have a Capristo stage III and hi flo cats. Any thoughts on where to diagnose? Hasn't thrown a CEL or SDL in months and I just replaced the O2 sensors and one thermocouple a couple months ago. It definitely feels like it's running rich down in low rpm but clearing up in higher revs? Thanks for any direction!

 

Perhaps a plug / wire / coil. If you are not getting spark, you would have un burnt fuel and rough running.

 

sounds like not running on all cylinders...could be even whole bank dead.

 

It's definitely not a whole bank dead, that has happened to me before and it was far worse than this. It still revs smoothly just stumbles a little under 2k and fine over that. I'm dreading the hole in the header as the culprit but I would think tone change plus more exhaust smell and weird idle might be just that?

 

Don't think a hole in the header would cause a stumble. But, we aren't there to feel the "stumble"

 

It's only when the car is idling and if in neutral. If I blip the throttle, right on tip in it just stumbles for a second at 1100-1200 and then revs fine. Sometimes it's accompanied by a light squeal which goes away when the hiccup occurs down low.

 

I bet it's the throttle position sensor, you need to remove it and clean it or replace it,

 

Where is it on the car and what is best to clean it with?

 

This is the part #158170, on the 95 355 there are 2 of them. You will have to remove the air intake to gain access, take a look at the diagram https://www.ricambiamerica.com/car-diagrams/ferrari/v6-v8/355-group/f355-m2-7-1995/throttle-holders-and-controls/158170-potentiometer.html it's a very easy job, should not take more than 30 minutes.

I paid $27 for a new one, but cleaning it with this item CRC 05111 Mass Air Flow Sensor And Throttle Body Intake Cleaner, should do it.

 

You can only clean its 3 pins. If this does not help, connect an ohm-meter to 2 of the 3 pins (find out across which 2 pins the resistance varies with the opening of the throttle). The resistance should change smoothly as you move the throttle. If there are any breaks in the resistance variation (especially while you move off the idle), the sensor is bad and you need to replace it. An analogue ohm-meter is much better for this test.

 

Great! I will give this a try, thanks guys. I read an older thread where some similar symptoms ended up being cam timing off just a bit. If that were the case it wouldn't just pop up out of nowhere correct? I would think it would have had to have been off since the last major and this car has been fine for a few years since?

 

Just a thought, check your ignition wires. I experienced a similar condition and found that the bottom side of one of my wires must have come into contact with heat and was slightly melted.

 

Update!

Mechanic tested both O2 sensors and the passenger one was reading nil to dead. Driver side was good. He swapped both O2 sensors and it stayed bad on the passenger side!?!? What could cause this?

 

Wiring

 

This is why sometimes you need an SD 2, a breakout box, or some positaps. So you can actually see what signal is reaching the ECU.

What stayed on the passengers side? You said there were no codes of CELs. So how do you know it's the passengers side? Part of the story is missing here.

Also, hard to believe an O2 sensor was dead and no code or CEL. Could be the mechanic damaged the sensor when he removed/tested it. Once reinstalled the O2 code/Cle would take a while to come on unless it was the heater circuit that failed.

 

There was a code stored in the computer but the CEL never came on, that's how he knew to check the o2 sensor. Not sure why it didn't trip the light?

 

What year is the car? If 96 and up (OBDII) will have pending codes

 

1995 2.7

 

Apologies as I see the thread title has 95 in it.

 

Maybe cel bulb is taken out I know people have done that. If it lights with key on then its good.

 

What was the code?

 

that was my thought.

sjd

 

Spoke to my mechanic and he said the driver side kept a 1211 code and the passenger side a 1114. Lights didnt trip and bulbs do work as the CEL's come on when i start the car for a couple seconds and then go out. He ran a temporary wire to see if the wiring was an issue direct to the o2 sensor and that did not cure it either. Does the ECM need codes cleared before it will talk to the o2 sensor again?

 

1114 is bad O2 sensor. 1211 is Lambda control. Typically a bad O2 sensor. However,

"This code is stored when the DME detects excessive

deviations in the air-fuel mixture (too rich or too lean) for longer

than 10 seconds. Possible causes: Fuel tank ran empty,

Incorrect Fuel Pressure, Injector valve defective or coked,

Engine Temperature Sensor defective, Secondary air leak,

Fuel evaporation control system defective, Air Flow Meter

defective and/or the combustion is being disturbed by

mechanical failure (Spark plugs,, compression,

intake/exhaust valves, ...etc.)"

 

i had a 1121 1211 on both banks and surging issues. Cleaned maf with maf cleaner and all codes/ surging resolved!