Odd Idle Issue

[KEast]

Guys, I am hopeful someone may have some insight into a nagging issue I'm having with a 522" stroker motor.

The car has a fairly aggressive cam, stryker heads, and a DC Performance tune for the 522 motor. Since the motor was built and with two tunes/computers there is one issue that I can not work out.

The car idles at 800ish RPM perfectly (its got a slight lobe but idles well). If I just barely touch the gas (I mean like just rest my foot on it lightly) the card idles down like it wants to stall. I notice it mainly if I am decelerating/coasting coming to a light or just sitting at a light and resting my foot on the accelerator in anticipation of a green light.

If you tap the gas it instantly revs with no sign of hesitation. You really have to just barely touch the throttle to see the problem.

Other then this issue the car runs extremely well and pulls like crazy all the way to red line. Its very easy to drive with just slightly more bucking then stock if Im lugging the motor.


Any ideas?

Thanks,
Kevin East

 

[Kenneth Krieger]

Kevin,
Make sure that there is a freely moving throttle cable with no "lag" in it's motion. Had a similar problem and realized that the throttle cable was not "taught" at idle and seemed to get "pushed" when just lightly touching the throttle and had a similar response. Let me know it this is your fix.

 

[KEast]

Ill check that in the morning. I looked into this a bit more today getting under the hood and could re-create the problem at the linkage. What I noticed was that the issue is actually a little different the described.

If I just barely (I mean as lightly as possible) turn the linkage I can simulate the in car hesitation. If I stab the throttle off idle there is actually a second where the car seems to hesitate then snap to life. If the care is already off idle it responds instantly.

If I would describe it from under the hood its a very slight hesitation "bog" when you snap the accelerator. The engine will die if you hold the throttle just barely touched.

Could this be an issue with some off-idle setting on the computer or perhaps some type of vacuum related issue with the PCM not seeing the change and reacting?

 

[KEast]

Is there a setting in the PCM that would adjust the fuel/air map right off idle.. If this was a carbed car I would think they jets were just a touch small.

 

[Viper Specialty]

Sounds to me like one of the base fuel map cells is causing your issue.

And yes, there would be a cell for that exact manifold pressure and RPM. Cams skew the map range, and are quite difficult to "long-distance" tune as they almost have to be written from scratch.

Sounds to me like someone did a quick idle tune for the cam based on adaptives, and didnt bother with everything else.

Other than that, check the TPS with a scanner for proper function.

Can you give us any more info? Injector size? Fuel system changes? Any other controllers (VEC-2/3) in the system? etc...

 

[KEast]

Thanks for the response FinalGTS.

The engine was built by Port Pros in Austin and tuned by DC Performance. It was a long distance tune based on the Dyno sheet we provided. I will be calling Chris to talk with him about the issue. DC Performance has been outstanding to deal with so far and I expect more of the same. It is only running the base PCM re-tuned.

The motor is 522CI with Stryker heads. I will get the exact cam spec from the build sheet and post it later today. The injectors and fuel system are stock. I was told the base fuel system was good for 600-625RWHP and my last dyno was 547 (this was before this last tune which has made the car drive/feel much stronger).

I will also get a TPS reading (I think my scanner can get this from the obd-2 port).

I did consider getting slightly larger injectors and having the computer tuned for them. I thought it possibly would be better from the injector drivers to not have to work quite as hard.


Kevin