Been helping my brother with his 02 trans am while he's away at work, and we just put a cam in it (don't know the specs, but it was a mild one) and got it tuned. After the tune, it now idles high until stopping. Start it up and it's around 850-9, start driving and then it hangs up between 12-1400 rpm and won't drop back to under 1000 until the car comes to a complete stop. I can have it in 5th gear not touching any pedals and it pretty much will hold speed at 40 mph. Going through a parking lot, 2nd gear idling everywhere. Not until after the car has been stopped for more than a second will the idle drop back to where it should be. Sometimes though it doesn't and will stay at 1200. It acts the same with the AC on or off. Also, since the tune it will get a dead spot right off idle every now and then where it will almost die. If it does it while trying to pull out into traffic you have to put the clutch in to get some rpm's and then dump it, otherwise there is no power until it's over 2k.

There is no check engine light on, and it didn't do any of this until after tuning which is why I'm wondering if it could be something with the tune or something with the car. We also put a new clutch in and had to break that in before getting it tuned, so I drove it 200 miles before the tune and it never did any of this. I took it back to the tuner once already because on top of the problems I mentioned, it was also randomly stalling when putting the clutch in if you were coasting to a stop. They claimed it was a dirty mass air flow sensor and that they cleaned it and adjusted the throttle cable. Didn't really seem to care about making it run right. The aggravating part is that since my brother moved down here with me, the tuner he used is 2.5 hrs away, and really not trying to spend money all over again to get another vin license from a local tuner to re do it when the shop we went to was supposed to be great.

it's an 02 trans am with a t56, long tube headers, ported throttle body, and not sure of the cam. After the tune it put down 399.8 on the dyno.

So my basic question is, does this sound like an issue with the tune or is there something I can look to that will fix it?

 

https://ls1tech.com/forums/pcm-diagn...high-idle.html

I've been fighting the same issue for a while, and I'm not a tuner but I do have HPTuners and have put in quite a bit of effort. My car did the same, drove fine after a professional tune, then everything got wonky, and that prompted me to buy HPT since I love doing things myself and had a desire to learn.

And for the record, I never did manage to fix the issue.

 

I'm in the middle of tuning my lq9-228R cam, LT headers and I had these symptoms. To me, the issue sounds like the Throttle Cracker table in the tune was raised in an attempt to prevent the stalling as you came to a stop.

TC has an activate and deactivate mph. Sounds like deactivate is set to zero? There's also a decay rate(how fast the effect of TC goes away). The cruise control effect you have at 40 mph may also be contributed to this table...it's asking for extra airflow when you don't really need it.

I think it's tune related, but only because the symptoms you are having are what I had (but I did them to myself by tinkering with the tune). Ask the tuner to email you your tune, if you post it there's tons of people here that are awesome at spotting irregularities.

Good luck.

 

Just checking back with this post, as I am chasing the same issues and never seem to see a fix for it. Did any of you figure out what the issue is?

My LS2 6.0L swap will fire up and idle at ~900 Rpm for 4 seconds, then cut down to ~725 RPM and idle (with a small amount of surging until warmed up). When driving, when I press in the clutch and come to a stop, it will idle at about ~2000 RPM until I come to a complete stop, and then drop back down to about ~900 RPM for ~4 seconds, and then finally drop back to ~725 RPM.

This is really inhibiting my ability to drive it, as at a stop light or stop sign, it sounds like I a am a crazy person...or a drag racer.

 

Are all the vacuum ports plugged on the front of the manifold?

Sounds like vac/unmetered air leak.

 

Couple of things can cause this:

1) Too much base running airflow
2) Too much timing in the idle cells or the cells near idle (either in the idle spark table or the main spark table - especially if there are different)
3) Too much follower airflow - typically zero out cracker and follower under 1600 RPM columns

It won't return to idle until the idle routines are allowed to kick in. That means it's a transition to idle issue with either too much airflow or timing or combination.

 

I have the exact same problem and havnt figured it out yet. I've checked for vacuum leaks, replaced tps and replaced all the intake gaskets. I've read through this site and havnt found a solution either

 

did you look at any of the stuff Jake just posted?

I have seen this issue in other people's swaps and thus far it is nearly always the case that someone got a cam and the tuner bumped the idle and fudged the main VE to make it run ok, but left the spark tables stock.

 

I was playing with my new cam last night and it reminded me of another thing I had forgotten about and took me a while to tune with my bigger cam... if you end up running rich in the 400-800-1200 cells but lean right next to it, the car will start to surge. You need to make sure you have a smooth gradient at 14.7-15.2:1 A/F. The safer option is to make sure you're slightly lean everywhere in those cells so the car enters a lean condition as it approaches idle. Of course, if you take too much fuel out, you loose some off idle tip-in. So it'll take a little time to get it right.

MAF shouldn't really have that problem as long as you've tuned the transfer table. And if you're closed loop, the O2s try to keep it around the same area. But still tune the VE and MAF to keep you lean in open loop so when CL is enabled, you still run.

But it's definitely related to swinging A/F issues. With the new cam. I can run rich everywhere... like 13.5:1 at idle and it does fine. But if I start to lean out some cells to 15.1:1 and then drive it, it's a no go. The oscillation is too great and sets the car off. Also, make sure you tune your 400 column. Idle your car down with bi-directional to 600 if you can to touch them. Then adjust the whole column up or down 2% at a time to see how it does. Rev. Rinse. Repeat. The slop of the curve (falling off hard down toward 5kPa and sloping up at 100kPa should mirror the 800 column and not the stock tune).

 

yes[QUOTE=truckdoug;19423334]did you look at any of the stuff Jake just posted?

I have seen this issue in other people's swaps and thus far it is nearly always the case that someone got a cam and the tuner bumped the idle and fudged the main VE to make it run ok, but left the spark tables stock.[/QUOT

Yes I did read. But mine just started having this problem abou 3 months ago. 2 years after the last tune. It was running fine until then.

 

Something else may be going on.

I randomly chase ghosts because my wiring harness has a short in it for the TPS. Makes it fun when it goes apeshit.

 

Yes, first chase down any physiical problems before thinking about plsyong with the tune.

 

I havnt had the chance to check this but i have the same issue and i think its because i combined and relocated the grounds on the back of the heads because i thought it would be easier than putting them back correct. I read this has caused idle problems for some because one of those grounds is for the tps and when not grounded correct causes irratic idle.

 

I also had the same exact issue going on after motor work. What fixed my issue was a new, different, throttle body. Night & day difference.

 

​​​​​​​very interesting. I did combine the grounds on the back of the head on pass side about a month before the prob happened. Don't remember how they where now though

 

I am fighting the same issue with my car right now. Tuned twice and still a problem... idled fine but once rolling, my RPMs would shoot up to about 1700 (experiencing the same "cruise control effect") until a second after i stop. They swapped out my Nick Williams TB with a FAST 102 (with new IAC) since they said my original was bad. Well then the SES light came on about a mile down the road after i picked the car up from them. Tried resetting and nothing helped. For time being, I waited until the car was nice and warm and idled down where it should be and i disconnected the IAC. Drives like a dream and no more annoying high idle! Cold start up sucks but now it drives so good and there is no SES light on which i find weird but hey..whatever works!

 

The cruise control is usually the Running air flow table being off. That takes a few cold starts to get right and usually when you get your car tuned by someone else they rough in what they think the numbers will be but may no go back to it unless you leave it with them for a few days

 

Did your problem start after the TB swap or was it doing the same thing?

I'm not trying to say what the OPs problem is. Just my experience with my car. My problem was happening with the FAST 92 TB. I did the relearn, I swapped the IAC valve, no change. From info I found here the FAST TB may be the culprit. I ordered a new NW 92 TB. Problem solved.

FAST TB: same racing idle, around 1600, until complete stop. Normal idle.
NW TB: idle hangs around 900, until complete stop, then drops about 100rpm.

 

Friend of mine had an issue with air leaking past the FAST blade. He ended up epoxying to close the air gaps. Fully closed blade you could still see light around the edges like a solar eclipse

 

You should log STITs whether you do RAFIG or when you're driving around. With RAFIG you can just let the table populate. But if you're logging STITs and LTITs, you can watch your car when you come to a stop and see what it says. If it's over 1g/sec off, adjust your base airflow.

If you do have an aftermarket TB, make sure it's set up properly. Take your IAC Steps table and move it 5 cells to the right. And then adjust your stopper until you're at 60 counts hot at idle (in drive with an auto). And that you're still within 1g/sec STITs.

If it's still hanging, you need to reduce your cracker tables under 28mph to 0 in the 400, 1000, and 1600 columns. You don't want any airflow adders coming to a stop (only if you find you're overshooting do you need to add a little airflow to soften).

Next, make sure your timing from High/Low spark to idle is all the same. You don't want spark jumping around or jumping up.

Next, put your rolling idle about 150rpm above your actual idle. That way on coastdown the PCM will try to hit it until the cracker is disabled and adaptive idle comes into play.

And finally, make sure your VE/MAF tables are at stoich or slightly lean. And make sure your approach down to idle cells is also stoich or slightly lean. Any hiccups there can cause an interesting landing to idle.