7_Zero

Car has had a hard time passing emissions the past couple of years and this year is no exception. 02 sensor and cat were replaced a couple years ago, put a new K&N filter in last month and have been running Sea Foam in the tank every couple of tanks for the past couple of months. Mechanic says that it passes high ok, but has a problem when idling. He says that it is misfiring and running lean at idle. He thinks that the injectors are not spraying right and that a pressurized cleaning will possibly do the trick, but there are no guarantees. I know that my EVP wasn't reading right, but the mechanic said that this wouldn't effect it since the problem is at idle.

Before replacing the air filter, codes read that system was running rich, and now that the filter has been changed, the mechanic is saying it is running lean. Not sure what is going on, I tried to pull codes, but now my code reader will not communicate with the computer.

Before spending $90 bucks to have my injectors cleaned, I was hoping you guys might have some ideas on how to fix the misfire and get this to pass? Also any thoughts on why my code reader will no longer communicate? Thanks for your help.

mudvayne1

Have you changed your plugs and wires?

trashline

I think those "cleanings" are a joke and cause more harm then good. You need to Check your TPS voltage. this a N/A mustang or turbo? Check fuel pressure at idle and while driving.

As stated a fuel tuneup would be a good idea too.

I am also assuming the EGR is hooked up right? You might try to remove the valve and clean that with some carb cleaner. while your at it clean the IAC too.

7_Zero

No, I haven't changed my plugs and wires yet. I have changed them every year right before inspection and figured it hadn't done the trick before so I wouldn't spend the money on it this time.

This is an n/a engine, pretty much all stock. The EGR is hooked up right as I just got it back in working order, wasn't getting any vacuum, but it is working now. I cleaned the valve with carb cleaner, and I am thinking that some of the cleaner might have made its way to the EVP, not sure though but I am thinking that is the reason it isn't reading correctly. The IAC hasn't been cleaned for a while so I will clean that out, check the TPS and get back to you, thanks for the tip.

dreamer1uk

Hi,

What year is that Stang again? Id try to pull those codes and go from there.

Any signs of vacuum leaks?

What everyone suggested is a great starting point, particulary the EGR and for the fuel pressure.

Id also recomend running a 92 Octane too as thats more of a controlled burn and will help with some 'misses'. One of my instructors at college went into great detail over the differences in Octanes. Pretty interesting stuff too.

I forgot to ask, when was the last time you changed the PCV valve? as there known to cause issues at idle is there gunked up.

7_Zero

Long story short, it passed today hurray!!!....but barely.

I checked the TPS and seem to get different results depending on the day. Tested it with the engine warm and got 1.33 volts. I was kind of excited because I thought that would fix the problem. Checked it again today with a cold engine and got .97 volts. Took it for a drive and got the engine up to operating temp and got .93 volts. Reset the idle screw and readjusted the TPS back to .97 volts and took it for another drive, now I get .99 to 1 volt. I think the sensor is good, but I cannot get the screws tight enough to hold it in place, they didn't give much room to get tools in there. Grrr.... Anyway, cleaned out the IAC, it wasn't too bad but did need a cleaning. Also dropped the timing a bit. All of this seemed to help smooth out the idle, which it usually does but it is just part of a cycle as it is only a matter of time before it starts acting up again. I guess most importantly it passed, but it would still be nice to figure out what is going on.

In answer to dreamer,
It is an '88, and I wish I could pull codes but after getting it back from the mechanic, my code reader will no longer communicate with the computer. Tech support for the reader said there must be a bad ground connection for the computer.

I am not hearing or seeing any signs of vacuum leaks, but that doesn't mean they are not there. PCV valve was changed a couple of years ago, and seems to be working fine. Right now I am running 88 octane, there is controversy over the whole octane rating and what not so I figured that any higher would be a waste, maybe next time I will consider it, or if it fixes the misses and bad idle I may use it regularly. Guess it wouldn't hurt to try it for a while.

trashline

Ive always kept my tps at .95 volts. I went to sears bought a cheaper phillips screw driver. I cut the handle off so I have the long metal driver parts and like 1" of plastic handle works GREAT for setting tps. I loosen one screw and then loosen the other. The second screw I tighten back up so that it is snug and will hold the sensor in place. Then I tap it with my screw driver to move it once set I go back and slowly and carefully tighten both screws.

If your running maximum stock boost or higher you need higher octane fuel when you have normal timing set with spout out.

trashline

damn ignore the fuel boost thingy lol this turbo 2.3L and N/A 2.3L mix confuses me.

dreamer1uk

Hi,

Did you ever test the TPS with a Volt Meter or Ohm Meter to see what the voltage or resistance is when you turn the plenum?

Most TPS's work off a 5 volt reference. You should see a steady increase in voltage or resistance as you turn that plenum.

I can get more testing specs for you off Alldata if you need it.

sah22588

my 88 gt straight up wont idle!!. i swear ive tried almost everything. cleaned the idle air control, bought a new throttle position sensor, new spark plugs, cleaned the tb, new fuel filter, ive got like ten month old gas in there so i added 4 gallons and put in fuel cleaner (heet). now i guess im just gonna have to check timing and check fuel pressure.