waddisme

Would like to try to diagnose myself as it is a 2 hr trip down and back to tuners. New motor has about 3k mi and has run smooth for past 7 mos. But last week, it started surging to around 2k rpms when I depressed clutch to stop at red light. In about 7 seconds, it will return to normal idle. If I am coasting up to a red light, it will stay around 2k rpms until I stop, then 5-7 seconds later, it will return to normal idle. It only does it when car is moving. I have sprayed every hose, TB connector, intake manifold etc with tb cleaner but nothing. It only kicks into high idle when car is moving - even if in gear. There are no codes. Search showed nothing except for coolant sensor but mine appears to read correctly.

I do have a GoPoint Bluetooth scanner I hooked up to car. Intake manifold pressure doesn't seem to fluctuate abnormally so I don't think it is a vacuum leak. O2 sensors are all within voltage range so I don't think it is that. Scanner measure fuel trims, IATs, manifold pressure, TB position etc. Tuner thinks maybe a vacuum leak, but hard to tell as it only does when car is moving


Here is a vid of what it does. It usually takes it about 5 seconds longer to go back to normal idle. You can see it go to 2400 rpms when I depress the clutch.



Thoughts?

tblu92

Is your engine STOCK ? It is rare to have a "hanging idle " on a basically stock bolt on engine--
Especially if it was working fine for a long time and suddenly started idling high when stepping on the clutch-----
Most common issue causing this is if you have an oiled air filter and you recently cleaned and re-oiled it----Initially excess oil will get sucked onto your MAF wires and foul your MAF making it read wrong--the oil burns onto the wires and it will stay fouled
You can clean your MAF with Brake clean or TB cleaner and it will remove the burnt oil
If you noticed recently almost all the aftermarket CAI systems now offer an"oil less" air filter made from synthetic fibers -- these are all cleaned with compressed air. Even K&N now offers oil less air filters ( oiled is now old technology)
If this is not your problem report back---
It is common for cammed or LT header engines to have idle hanging or dying issues --If you car falls into this category it is fixable with tuning However it is rare as I said for it to be OK then start having problems
You said you checked for vacuum leaks which is usually the culprit BUT other than a vacuum leak you can suddenly have "un mtered air" entering your engine somehow
This can come from :
A faulty PCV system or failing PCV valve or leaking hose
A leak in your airbridge ASSY from a broken hose or mis aligned clamp
The air injection hose has come off your intake air filer ASSY or the hose is damaged

waddisme

Thanks for the detail reply. All of those things I have tried. Vararam was oiled when motor was apart 7 mos ago and has not been done since. I have checked every hose in the pcv system and have found nothing. I doubled checked the vacuum hoses at the back of the manifold and they all seem secure. All my connections from the MAF to intake are tight - no flex at all. Unfortunately, it is hard to trace as it only occurs when car is in motion. Will take MAF off tonite and clean it and the TB and see if that helps.

Thanks.

CTD

Are you game to pulling your intake, it's a ported Fast correct? Prior to pulling it have you checked the mounting bolts are snugged nicely? Only snug & even.

The Fast manifold have had some issues's leaking in between the halves & of course under neath where you cannot spray.

Your description does sound more like rolling idle which is a tuning thing. It would help if tried rolling up to a stop clutch in/out & in gear/neutral, clutch in/out. Sounds goofy I know but if you speak with your tuner he will guide you.

waddisme

Will recheck torque on Fast bolts tomorrow. Going to take MAF and clean and clean TB also. Not sure where to go after that.

Thanks!

waddisme

UPDATE -

Re torqued FAST bolts. A little loose but not enough to make a difference. Coasted down a hill, clutch in, clutch out - doesn't matter. TC on/off doesn't matter. If car is moving, it stays at high idle. Once car is stopped, in 5-7 seconds is goes back to normal idle. I just lifted it onto jack stands, started it and put it in gear. Once rear wheels are moving, it stays at high idle once clutch is depressed and stays until brakes stop the wheels. It is too late at nite now, but at least I can look for a vacuum leak now with it in high idle! Checked again and there are no codes. Seems like someone should have run across this before.

waddisme

Got a chance to check for vacuum leak while it was in high idle mode - nothing. No apparent leaks. Looks like I am off to tuners.

CTD

Would your tuner consider helping you with email tune? Depending on the software they are using it would make dealing with minor glitches easier from your end.

danh52

Please report back with what you find out about this issue. Thanks

waddisme

Tuner can do an email scan if I had HP Tuners, but I do not nor can I find anyone local who does (small town). Have appointment for Sept 1 to have them look at it. In the meantime, I will keep checking all I can. Plugged up PCV outlet from intake to see if it was leaking, but nothing. Same with EGR hose - nothing. Borrowing a MAF from forum member and switching that out to eliminate that from equation. Will keep checking all that I can before Sept. Will post all that I do just for future searches.

waddisme

Unhooked MAF and took a short run - same problem, so probably not MAF.

Replaced Air Temp Sensor as search found a thread where someone was having the same issue caused by bad temp sensor. Nothing.

Went ahead and repl other O2 sensor, even though I know it wasn't that, but had it anyway.

Pulled brake vacuum hose to check for cracks as it runs across some metal etc, but it looks all good.

Pretty much done with self diagnosis. Will report back with what tuner finds next month.

Thanks for all the input.

waddisme

Just to clean this up for future searches, my FAST intake had a crack in the very back where it is underneath the cowl. Not wanting to wait for repair, I repl with new FAST and all is good. Could have saved myself some money by taking CTD's suggestion and pulling intake myself.