Hello everyone. First off I would like to say I have done tons of research/reading on the board before I decided to ask my questions.

About a month ago I bought 96 Z28 M6 102k on it. The car has had a high idle and smells like it is running rich.

So I went to work to start trying to figure out what was going on. Pulled the codes got a P0420,P0430, and the IAC code(forgot the #). I removed the throttle body cleaned it and the IAC. During that I found the rubber elbow was torn so I ordered the Jegs elbow. Once I installed that and clean Throttle body and IAC the IAC code went away. Still have the P0420 and P0430. Im not to worried about those bc I know the Cats need to be removed.

But now I have P0171 and P0174 Intermittent. Still have a high idle 1200-1300rpms.

I have change PCV valve checked everything for vacuum leaks (sprayed starter fluid in multiple locations) inspected the MAF looks super clean.

Car runs great. The high idle and P0171/P0174 are bothering the crap out of me. Anyone have any ideas. Or is my only choice hooking it up to a scanner...

thanks for the help
Matt

 

Those codes indicate lean conditions on both banks. That and the high idle makes me think intake leak. I know you looked for leaks but did you check the hose to the power brake booster. That could be a pretty big leak, enough to raise the intake and have the engine run lean. Also look the the throttle body...they can leak at the point where the throttle shaft rotates in the body.

Do you hear any unusual hissing noises? I'd think you would with a leak big enough to do this...

 

The idle related codes are P0506 (low idle) and P0507 (high idle). Those codes indicate a low or high idle speed, outside the programmed value. They aren't really "IAC" codes, they are idle speed codes. The cause of the high idle is most likely a leak in the system, not a problem with the IAC, unless the IAC is stuck fully open.

This will tell you if the IAC motors are burned out:

Courtesy of Shoebox

http://shbox.com/1/iac2.jpg

The lean codes set when the PCM has to add an average of 22% more fuel than it would normally add. That's a huge error in the incoming air flow measurement. Have you cleaned the MAF sensor? The tear in the rubber elbow would also allow unmeasured air to enter the system, inflating the long term fuel corrections, but would not cause a high idle.

 

The brake booted hose appears to be fine. Also the throttle body seems to be fine. No hissing... even when I apply the brakes.

 

p0507 was the code it was giving me. That code went away after cleaning throttle body iac and replacing the intake elbow.

The MAF has not been cleaned but it looks spotless. I actually bought cleaner but looked at it decided not to clean it bc it appears to be clean.

 

I have a scanner that will do freeze frame and record data but I have no idea what I'm looking at. Any place I can find info On what values I should see

 

I forgot to mention this but "sometimes" in the morning the car will idle fine when I first start it up. Not all the time but sometimes.

 

Post the data and we can tell you what it means. A single frame of data is not always useful. A longer term data log (5 minutes) is best.

 

Ok I will try and figure out how to do that And I will post it.

 

Quick question...did you clear the codes after cleaning the MAF and replacing the elbow? Some don't go away even after fixing the fault.

If you don't have a scanner handy just disconnect the battery for 30sec or pull the PCM BAT fuse.

You may want to capture data before and after clearing the computer....

 

Yes I did clear the codes. And I just cleared the codes again and went for a 25 mile drive and nothing came back up. Thing about that is normally would get the light within 5-10 miles after resetting the codes. But I hooked up a scanner and took a few pictures of at idle and cruising at 65-70 mph. Im working on trying to upload logged data but cant find the cord.

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Car still has a high idle even with out the check engine light

 

IAC fixed high idle. No new codes yet. Probably going to need a few more drive cycles to see how everything else goes. Good step in the right direction at least

 

Appears its maxed out the long term fuel trims, adding 25% extra fuel beyond what it calculates is normally needed. Either the fuel pressure is way low, or there is air entering the engine that is bypassing the MAF. Could also be faulty O2 sensors, exhaust leaks before the O2 sensors, or injectors that are smaller than what the PCM is programmed for.

When checking for vacuum leaks, did you check the bottom of the injectors where they mount in the intake manifold?