cams and some other things have a big effect on how much vacuum you will pull at idle. Another thing is i have seen many mechanical vacuum/boost gauges go bad, so if yours is mechanical you might wanna verify you are getting correct readings either via a MAP sensor or a different gauge.

 

motor is all stock. And the boost gauge is a defi electronic one and it seems to fluctuate in time with the lumpy idle. Is there a chance it may be the o2 sensor as the problem arises after the car warms up. Aprox 2 minutes after start up. And if I unplug the o2 it seems to improve the idle

 

That's definitely a possibility.

 

Would it be unusual for the o2 to fail and not throw a code or effect driveability

 

Well if its only having trouble after it warms up, it could be that the problem happens when the ecu is in closed loop, which would be effected by the 02 sensor. The thing is, it should throw a code when you unplug the 02 sensor, but it doesn't sound like that happened? Have you tried pulling codes, because the CEL can go bad.

 

Sorry my bad yes it throws a code when I pull the sensor but no code for it being bad.

 

Ok gotcha, well when you pull the sensor it prevents the ECU from going into closed loop, so that is kind of a clue. There are other things that could be throwing it off other then a bad sensor though. Do you have access to a logging cable? Some data from when the issue is happening would be helpful in trying to diagnose the problem.

 

I do I have a cable and evoscan but I don't really know what I'm looking for. What would you think?

 

well the first things i would look at would be LTFT Low and Mid to see if they where both pretty close to 0 where they should be, second would be ISCV Steps to see if they where pretty stable durring idle. Then i would look to see what the ignition timing is doing, is it bouncing all over the place or is it also somewhat stable. So go ahead get it warmed up and take a log of it, you can go ahead and post up your log and ill take a look and tell you what i think could be going on based on the log.

 

I will surly do that. Thanks very much will post when I have It done.

 

OK so timing advance is pretty steady but goes between 4 and 9 sometimes.
.ltft low 10.9375
Mid ltft. 0
Ltft high.0
Ltft in use. 10.742
Oxygen feedback trim. -.3906
Isc steps pretty stable going between 50 and 60

This is taken from a warm idle
See what you think thanks again

 

that LTFT low is way too high something is definitely up there. Try warming it up, shut it off pull the battery to reset the trims and then let it idle again for 20 minutes and see what that LTFT low does. If it goes back to still being high like that then you probably have a fueling issue. Bad sensors will typically spike the ltft at + or - 12.5 which is the max, so im not too inclined to think its a bad sensor, but if you have a wideband to take readings to verify what the narrowband is reporting that would help eliminate the possibility of a bad 02 sensor.

P.S. fueling issue could be something as minor as bad gas or something worse like a clogged injector etc etc.

 

Yes I have tried pulling the battery and letting everything reset to no effect unfortunately. Any tips on testing injectors. Is it possible to be a fueling issue when there is no loss of power or driveability?

 

yah, thats kind of the point of the trims, the ecu is adjusting to the conditions and trying to do what its suppose to and since its pretty minor the ecu is coping with it. Your LTFT Mid looks good which means what ever is going on is minor enough that its not effecting your fuel map much and if there was something more wrong you would definitely be seeing something going on with the LTFT Mid as well. As far as testing for a clogged injector, can't really do that without pulling the injectors. You could try running a fuel system cleaner for a few tanks and see if that makes a difference. Also if your getting your gas from the same place maybe try a different place and see if anything changes.

 

OK thanks so much. Appreciate it. I will try some cleaner and run it through will update after. Thanks again