Surging idle when cold

[Don GTP]

I have a 99 Grand Prix GTP with IS3 Cam/Heads, Northstar TB, 60/65 lb injectors, SLP headers, & other supporting mods, no IC yet though, also I removed the EGR completely.

Ever since I installed the Northstar TB & 60/65 lb injectors (along with editing the PCM for such changes) my car has had a surging idle, let me elaborate...

When I start the car up on a cold day (colder than roughly 30 degrees) the idle with surge up and down for a few minuites.

The colder it is ouside the worse the surging is, i.e. when the temp is like 10 degrees or colder the car will surge from about 600 rpm to possibly 1800 rpm for about 5 minutes, After a few minutes the engine finally smooths out and gets to stable rpm, the warmer it is the less severe the surging, at around roughtly 30 degree or warmer the surging is barely noticeable.

I set the idle via my HPTuners to about 900 or so.

I have dealt with the issue for a few years now but I would like to know if anybody has had a similar issue of a surging idle & has found the answer & fixed it.

[bilemke]

Have you tuned the VE table in you bin yet?

[BlackGS]

I have the same problem. Started sometime after the IC install, maybe around the time I put the fuel logs in with 65# injectors. Seems to be worse in Park/Neutral, and not as bad as soon as I put in gear. Some possibilities I've been investigating are

1. Dirty sensors (MAF, IAT, etc)
2. Timing too high at idle
3. Fuel pressure issue because of rails

Lowering timing seemed to help a small amount. I had previously increased timing in the lower rpm range, so maybe it was too high.

I currently am running a stock TB/MAF, but I have the Northstar waiting to go in, so I was hoping that might help also.

[Bandit gs]

Mine does it also, i've tuned the VE a little and it helps. I also think there might be a small vac leak that is causing it.

[z34phoenix]

from my reading on other forums and a friend who just installed a Northstar i modified for his car.... it is the PCV system that is causing the issues... im assuming like most N* installs the stock PCV system is blocked (air source is thru the TB on the stock l67 setup. and further more runing a breather in the valve cover allows unmetered air thru....

to solve this issue for my friend i used QuickSteel (similar to JB weld but a puddy) to add material to the N* so i could drill an air passage so i could allow the PCV system to operate like it normally would on the stock TB. he has had no idle issues with that setup.

*** Yeah! my first post!***

[JerryH]

On a poorly designed adapter, yes the PVC passageway between the TB and inlet could indeed not exist. There are a few various ways to handle this, one good example right above my post, but the best way is to integrate this passageway into the design of the N* and S/C inlet.

For people that purchase these kits, this should be one of the first questions to ask before purchasing. VE tuning is a bandaid for the condition, it doesn't solve it. A good train of thought is... never try to tune out a mechanical problem, it could turn around and end up biting you back.

[Trannyman95]

I have had adapters made for using N* throttle bodies for roughly 4 years. I have had them with with and without the pcv passage and it has made no difference in the idle qualities. Some cars work fine and some are very sensitive to the change. Idle airflow tables need to be adjusted as the IAC is different as is the pintle valve on the end and these tables NEED to be adjusted to make it run properly which is why I have been asking for a very long time for these tables to be added to the tuner. It helps a little bit if you drill a hole in the throttle blade as this lets more air in the engine. One major problem especially with a larger camshaft is that you need more air entering the engine, so even with a stock throttle body this needs to be adjusted to get the car to start right and idle better. The car acts like it is too rich and pushing on the throttle pedal a slight bit will let the car start right up and idle ok. Its not that the car is too rich, there just isnt enough air getting in.

[midgetracr]

Trannyman, what size hole did you drill?

[Trannyman95]

I think an 1/8" hole is what I have used in the past. The LS1 throttle body on my cutlass with L67 already had an 1/8" hole and when I plugged it the car didnt want to start without opening the throttle a bit so I opened it back up.

[damojo2003]

My idle would surge like an sob on cold starts. What I did, other than a ve tune, was to lower the idle spark 2*-3* and I adjusted the maf below the idle range. SO if I idle about 2800 hz and I have a change from the stock maf of 3% @ 2800hz, then 1500z to 2800hz had the same 3% correction. O...I also increased the time for closed loop.