Xtreme57

iTrader: (6)

A little backstory -- my car broke a valve spring a few weeks ago, but before I found it I thought it might have been something to do with the MAF/airflow based on the way the car was acting. I cleaned the MAF, checked for leaks, and replaced the plugs/wires before finally pulling the valve cover to find the broken spring.

Now it has started throwing a P0507 code, and idles extremely high when the car gets put into neutral (1500 rpm or so), and will only drop back down once the car comes to a complete stop.

So from searching around here, it seem a lot of you guys have dealt with a P0507 Code (High Idle) on an LS1 but every thread ends the same way -- people make several suggestions and the thread just ends without any resolution as to how the damn problem got fixed. I checked for vacuum leaks, replaced the IAC sensor, and made sure all the connections were secure.

I did find a stripped valve cover bolt, but I don't think that would allow air into the combustion chamber. It seems strange that only after I found the valve spring that this all started ... but I cannot figure out wtf is causing this and its driving me insane. So can any of you that actually SOLVED this damn problem please give me the heads up on how you did it?

Thanks.

RPM WS6

iTrader: (3)

I had this problem once, but the idle didn't hang quite as high as yours. Here is a link to a thread I wrote about the condition:

https://ls1tech.com/forums/general-m...rt-needed.html

It's a long read, so here are the cliffnotes:

EVAP purge solenoid was apparently allowing more flow than commanded, though it did not trip any EVAP codes. I know I state in the thread linked abobe that I was not getting a P0507 at that time, but this condition had in fact caused that code to trip on previous occasions. I dealt with that issue on and off for many years before narrowing it down to the EVAP system.

Again, my idle was never has high as 1500rpm, but it seems that you've already looked at all the more common fixes so this might be something to consider even in your case. My testing results, detailed info and a part number for the solenoid are all located in the above link.

Good luck.

Xtreme57

iTrader: (6)

Hey thanks. So you just changed the EVAP solenoid and that did the trick huh? Well, I think I'm gonna order one and see what happens. How difficult was the change?

RPM WS6

iTrader: (3)

Yes, it seems that the purge solenoid was the problem in my case, although my idle was never as high as yours. It was a very simple part to change, took all of 5 minutes or so. It's mounted to a tab on the driver's side of the intake and attaches to the vapor line via quick disconnect on both ends.

Chaos07

Hey im having a similar problem, My cars use to idle around 500-600 and would surge a bit but it its normal range, well i swapped intakes to a FAST 92 and im idling high like around 800 so i adjusted the screw on the throttle body and it still idles like it has a leak somewhere. It wasnt throwing codes but when i hooked up my scanner it had shown a high idle code P0507 on it. could the EVAP system be the problem.

RPM WS6

iTrader: (3)

If the problem started immediately after the intake swap, then my guess is that something related to the swap is a more likely possibility than something related to the EVAP solenoid - unless the solenoid became damaged during the swap.

AmDWs6

wouldn't a tune fix that idle issue?

Xtreme57

iTrader: (6)

I had this issue a few months ago. I just got a brand new crate LS1 put into my car (for reasons other than the surging), and even after a brand new engine it is still surging.

Here is my experience and thoughts with this so far: As mentioned in the original post, I had my mechanic go over my car for a misfire code. He disconnected the battery, cleaned the MAF, TB, and obviously popped the valve cover. As also mentioned I replaced the engine, so a vacuum leak seams unlikely. I replaced the MAF with a new model, as well as the TB sensor. Both of these things actually seemed to make the surging WORSE than before.

I will tell you that one thing I found that does solve the problem is putting a piece of duct tape over the little hole in the blade of the TB. Obviously this is not a permanent fix, BUT it does keep you from going crazy. The tape seems to choke the car however (most obviously noticed upon startup).

I know some people think the EVAP system is to blame, but from all of the research I've done, it seems that this happens most often to people who do things to the TB/intake so it doesn't seem that the EVAP system has too much to do with that.

The tape over the throttle body seems to be the most telling piece of evidence I've found thus far. I am EXTREMELY curious to find someone that has had this problem and changed their throttle body to one that has a smaller diameter hole in it, or no hole at all such as a BBK model. I'm inclined to think that there is some hiccup with the ECU and the change in airflow, but unfortunately I'm not well versed enough in exactly how everything works in these cars to come to a better conclusion. Obviously the common answers seems to be vacuum leak, evap, etc, but I honestly think it something else.

If anyone has had this issue and changed their TB to something other than another stock LS1 unit, I would love to hear their experiences.

RPM WS6

iTrader: (3)

Did your new engine include a new intake as well? If not, then the problem may still be related to an intake vacuum leak.

The TB hole was present on every factory throttle body, and these cars didn't have surging issues in original, unmodified form, so I don't think the hole is to blame.

As for EVAP, I think it's a rare event that this is the problem. In my case though, it seems that this definitely was the problem, because replacing the purge solenoid fixed the issue. But my problem never behaved like a hard leak because I could correct the condition with a simple key cycle, so it made sense that it would be related to some sort of electronic vavle or sensor.

One thing I have noticed is that the PCM is sensitive to unexpected load changes, and will sometimes surge as a result of this. With an A4 car, in-gear idle surging can happen as a result of a higher stall speed converter "unloading" the engine to an unexpected degree with a stock tune. Surging is also a common problem with stock tuning and cam installs, or anything else that changes the expected idle dynamics.

It only stands to reason that if your issues began immediately after an intake or intake/TB swap, that the changes you just made are likely somehow the cause of the issue. For people that have changed nothing but were suddenly hit with this problem, then other areas such as sensors or EVAP should be the first areas looked at.

Xtreme57

iTrader: (6)

Agreed. Obviously in your case that makes total sense. In other's case, like you mentioned if someone changes an intake it seems hard to believe that the EVAP would then become problematic.

Another update, going back to the duct tape over the hole in the TB blade, with the advice of a friend I took it a step further. So with no tape, the car idled way too high. With tape, it seemed to choke the engine a bit. So, I put a tiny hole in the tape (thereby reducing the size of the hole in the blade) and THE CAR ACTS PERFECTLY. I drove it 30 miles and sure enough, idles perfectly in gear, when put in neutral even at speed where only two days ago it was surging to 1600 rpm.

So all I can figure is that the mechanic MAY have brushed or sanded or "cleaned" the hole in the blade perhaps and enlarged it ever so slightly, which would allow a bit more air through the hole and might have been enough to eff up my idle. The next step I'm going to do is buy an aftermarket TB or maybe even just a stock TB and see if I can confirm this once and for all.

dtmason ss

I had the P0507 code and my car would idle high wen in neutral until i came to a stop and found that the problem was a hole in the botton of the 2-3in hose that connects to the pcv valve now it runs great no more high idle.