Does the CCV system contribute to engine vacuum? I have a high idle problem and a loose ccv fitting in the pass valve cover and wondering if that counts as a vacuum leak that could be causing the high idle. Thanks

 

Post #9 answered your question in another thread.

https://www.camaroz28.com/forums/sho...d.php?t=690330

 

Thanks for responding. It only happens while the car is moving, idle hangs at about 2000, fine at a stop. I've read about 20 posts on this subject, resistance at the IAC is fine. Dont have a scanner. Car is race only - cant take it to 'the zone' to be scanned but I'm going there tomorrow, I ask if I can borrow it. I'm going to take the TB all apart tomorrow, clean everything, try Shoebox's reset then I'll let you know what happens.

 

The PCM elevates the idle speed when the car is moving (VSS not equal to "0"). Does your PCM run a custom tune?

 

yes, by PCM for less. So far I replaced every vacuum line that looked suspect, I tested the resistance at the IAT, I cleaned the IAT which was absolutely covered with oily crap, cleaned all passages, oiled the butterfly rod, I replaced the TPS with a spare I had lying around and I did shoebox's IAT relearn procedure - no change. I plan on switching out the IAT for the spare I have lying around this weekend. I don't have a scanner to check what the IAT is doing, I tried to borrow one from autozone but they don't have one to lend, Im thinking of trying advance. Now that I think of it this did start with this last engine built and this is the first with a custom tune. Do you think the PCM is just programmed to elevate the idle too much at speed? Of the 20 or so posts on this subject (high idle) two of them match my description perfectly (idle hangs too high only when warm and while moving - one was fixed with the re-learn and one with a new TPS - neither worked for me - a programming issue could explain that I suppose.

Also, I remembered that I used to run a breather in the valve cover on this car years ago (lots of us did to try to prevent the LT1 oil leak FWIW it worked for me) with no problems with idle, so I guess the CCV system doesnt contribute to engine vacuum.

 

Its IAC (Idle Air Control). IAT is the inlet air temperature sensor in the inlet elbow.

Do you still have the EGR system and EVAP system? If they have been blocked off, is it possible that one of them is leaking? Are you sure its not a throttle linkage problem? Does the idle speed drop when you blip the throttle on coast down?

 

Yup - IAC.
EGR and EVAP intact.
Wont kick down with a throttle blip.

So I'm really frustrated with finding a diagnostic software. I know I need to know the "steps" or whatever from the IAC while the car is rolling to see if its the programming that is running the idle too high while coasting. So far as I can tell there are only about three software program/adapter scanners out there. All are just like auto tap and are $150-200. BUT for that you only get like DTC's, to look at the IAC function all three require you to purchase the optional "extended parameters" for like $200 more bucks! Thats $350-400 bucks just to diagnose my idle problem. (the zone and advance wont loan me one of their 'stand alone' scanners.)

So then Im thinkin I'll just go ahead and get LT1 edit. But from what Im reading there is no scanning ability with LT1 edit, only tuning. So to successfully scan to check my idle parameters, then tune as I need, thats close to $800.00!!! for both. Is that right????

 

Alright, I know Im just ranting to myself here but Im OK with that. I called and talked to actron - they say none of their actron scanners will read the steps from the IAC. They say there is an autoxray that will thats like $4-600 on the web. For that I can get autotap + the enhanced GM parameters for like $300. I just don't get how I read EVERYWHERE on the forums "just check it with a scanner and see what the steps are set at" but no scanner can do it w/o spending $$$. I find it hard to believe every joe blow teenager on the forums is buying $4-600 scanners. I guess I'll just get auto tap, but I wouldnt mind having a handheld I could take to the track and record runs (harder with a laptop).

 

Just FYI - I talked to PCM4less and he suggested backinbg off the idle screw. Made no sense to me since it was only high idling while rolling. Anyway I took off the throttle body anyway to change out the IAC for a spare I have so I went ahead and backed of the idle screw as well while I was there. Now it is still high idling but for a much shorter time and not quite as high. When I get off the throttle it will still idle at around 17-1800 (before 2k to 2100) and for only about 3 sec when before it was like 9-10 sec. Also it never kept the high idle all the way back to the pits like it used to, it always settled back down. SO I dont know why the idle screw would have helped this but the programmer guy says it does. It would make more sense to me that it was a bad IAC but I tested the resistance on the original and it was normal. Anyway - FYI.