I have an intermittent problem... when I take my foot off the accelerator pedal the engine stops or idles very rough with puffs of black smoke.... A sensor problem ?

 

Could be. Find someone with a good scan tool and find out whats going on.

 

idles issues plague our cars, and there are lots of various culprits and scenarios. i personally always lean towards the air idle control valve (IAVC) which would probably need cleaning.

 

Don't you know that a 98 doesn't have a IACV.

I'd read the code first since there are puffs of black smoke other than the idle issue.

 

Any Codes? Try replacing your oil control valve

 

Do you even have a code (check engine light on)?
When is the last time you serviced/cleaned the throttle body?
If there is low idle leading to the engine dying then perhaps it's starved for air.
Black smoke indicates car is running rich and burning too much fuel.
Air filter clean and not plugged?
Cleaned the MAF sensor?

Or you could be getting too much fuel from faulty injector?
Possible broken/cracked vacuum line?

 

oops yes i knew that, thought the OP's car was older since the year was never mentioned. i now see the picture of a 98-up on his profile. my mistake!

i do suspect the car would not show any codes. what would be next to troubleshoot?

 

I think threads like this that have zero response and no resolution should be deleted.

 

No codes and have had the local auto elec plugged a code reader into UBD2 and nothing.
Where is the oil control valve ?..... What makes you think that ?

 

No CEL...
Never serviced or cleaned the throttle body
Its fueling up.. And its using more fuel.
Air cleaner is near new.
Never cleaned the MAF... its done 285,000km
Its also been suggested i should replace ALL 4 02 sensors

 

1. Clean the throttle body
2. Clean the MAF

Maybe you have a leaking/ stuck open fuel injector so then try a
3. a heavy dose of PEA containing fuel system cleaner such as Techron,Gumout Regane, Amsoil PI, etc

4. Temporarily try removing a couple of vacuum lines from the intake. This will allow more air in and may help your idle, if it does then you know the air flow is being choked off, probably by a dirty throttle body.

5. Get a scan tool or a Bluetooth dongle from eBay and use torque app will give you the reading from the O2 sensors will at least point you in the right direction.

6. Using the scan tool, check the reported engine temp from the ECU. Maybe your ECT, engine temp control sensor is bad causing the car to run in a cold start mode 100% of the time.

And how do you have a "UCF20R". Turbo? ROFL

 

A code reader is a nothing tool, other than just reading codes. If no code is there then that's it. A good scan tool can test many of the components and like brybo86 said its going to show what the O2 sensors are seeing and long and short term fuel trims which is a huge help in figuring out problems, temperatures etc. On the newer cars a scan tool can pretty much operate everything there is, just like the hacking stuff you see on tv. You can do tests like turn on and off the egr if there is one, turn certain spark plugs off and on (simple explanation), turn fans on and off etc. etc.

 

Looking thru my LS's service history a similar issue as yours required installing a new MAF. I'd try cleaning it and/or sourcing another from junk yard to test.

 

Faster and likely cheaper to do the scan tool thing, than guessing at what part you are going to change next.