Idle routines not kicking in everytime, HELP!!!

[LosLS2]

HELP!!!!!!

I am tuning an 8 sec street car here. Yes, my favorite. Anyway, I also have this problem with my car so I gathered some data so that you guys can see what I am talking about.

This log is of the car just sitting at idle in gear. You will see that the idle routines are working fine in the begining of the log. The car is in gear with my foot on the brake pedal. At the one minute mark, I engage the transbrake and give it a little gas (you can see the TPS% increase). Once I let out of the gas, TPS% goes back to zero. Idle routines kick back in (you can see the timing bounce around and the IAC counts go to zero or so). Rinse and repeat. The next time that I do it, the timing and IAC hang (main spark table and IAC steps vs effective area table values are displaying on the scanner).

I see that the TPS% is stuck at 1% but I have the Min TPS (under Main Spark Advance) set at 2% and have tried going up to 5% without any results. PLEASE PLEASE PLEASE help me resolve this issue!!!!! When the idle routines are working this thing idles absolutely perfect at 1000 RPM's.

[Frost]

Your TPS voltage is likely too high; ie, you have the blade open too far. It MUST return 0% TPS. I have seen them on the edge 'flicker' from 0-1%. Has to be just 0% at idle. Further evidence is your IAC at zero... it is trying to limit airflow, but it can't go lower than 0! Also, your idle airflow falls off a cliff at 140degF going from 19g to just 8.5-9.5 at normal operating temp, just pointing that out. Between that and the zero'd IAC, assuming there are no issues, you need to do idle airflow tuning.

[LosLS2]

Your TPS voltage is likely too high; ie, you have the blade open too far. It MUST return 0% TPS. I have seen them on the edge 'flicker' from 0-1%. Has to be just 0% at idle. Further evidence is your IAC at zero... it is trying to limit airflow, but it can't go lower than 0! Also, your idle airflow falls off a cliff at 140degF going from 19g to just 8.5-9.5 at normal operating temp, just pointing that out. Between that and the zero'd IAC, assuming there are no issues, you need to do idle airflow tuning.

There is no set screw in the blade so I can't get it anymore closed. I also have a return spring on it and manually pushing it closed does not cure the problem. I will log the TPS voltage to see what that says. Until I can resolve this issue, I can't address the idle airflow as the LTIT and STIT are disabled once the problem starts. If my idle routines were working and the IAC closed completely everytime, I'd be in good shape. My problem is getting the damn thing to close and getting the over and underspeed spark tables to kick in. Thanks for the help and I will check the voltage on the TPS once the problem begins.

[LosLS2]

Here's another log with TPS voltage (just add it to the supplied config file). I find that after I flash the PCM, even with the same exact tune, the idle routines always work until I crack the throttle. Sometimes they work again and sometimes they dont. Anyways, the TPS voltage shows .27v @ 0% TPS in the begining of the log and everything appears to be working correctly. I give it gas, voltage starts jumping between .25-.27 and 0-1% TPS and then it doesn't work anymore. It's like I am crossing a threashold but then I can't get back everytime.

[Frost]

Slamming the IAC shut is not desirable or the intent of it's useage. When it is at 0, the PCM is getting more air than it wants, it just can't can't cut it back anymore. The goal is to get it to the middle of it's operational range so that it can properly regulate airflow both up and down, not just up... If you get the IAC to 0, the underspeed table will never be used, since the only thing holding the RPMs down will be the OVERSPEED function.

You may be able to open up the mounting holes in the TPS a bit to be able to turn it slightly to reduce closed-throttle voltage.

[Frost]

I have seen that flicker before following the same startup at 0% behavior and then it won't return and stay at 0. It just needs to be lowered a tad. It would NICE if the upper and lower voltage thresholds were available to edit in the calibration

[LosLS2]

I understand what you are saying about the IAC going to zero but it works that way. It takes the IAC out of the equation and gives it a "floor" RPM. This cam has .700 lift and the duration is in the 270's. The IAC just isn't fast enough to respond when it is underspeed. You will note that once I get back to 0-1% TPS, the main spark table is being referenced (not the idle spark table) and the IAC counts go up to the setting vs Effective area.

I will try to get the voltage down. Seems odd that .27 is reporting 0% and .25 is reporting 1%.

[12secSS]

As Steve mentioned, your IAC needs to be active. What is this setup? What throttle body are you using? You need to close off air getting passed the throttle body, is ti drilled? Is there a vacuum leak? Also TPS voltage should be around .45V and .57V for idle conditions, it could be tripping a setting for too low of a TPS voltage.

[LosLS2]

It's a Nick Williams 90mm Throttle Body. It is drilled. Again, the IAC going to zero is a good thing for me and not the problem. The problem is when it doesn't go to zero and the idle spark routines do not kick in.

Regarding the TPS voltage, Frost is saying .25v is too much and you are saying that it is not enough.

So which is it?

[Frost]

No that is a low value, and I must have completely skipped it in reading. I have seen the exact behavior you describe though at the point where the TBs are open almost too far. In those cases the actual voltage was high, so I wonder if it is as George mentioned... There are more TPS-related values here that would be useful to have access to in many situations *cough*

[LosLS2]

We ordered a new tps sensor. I'll keep you guys posted.

[LosLS2]

OK, I put a new TPS sensor on the car. Start the car and idle routines are good and all is well. 0% TPS is being reported at .47v. Give it gas once or twice (in park) and then let off and the TPS voltage goes down to .41-.43 and the TPS% jumps between 0-1% and no idle routines. For shits and giggles, I pulled the plug from the TPS sensor and it settled right down. Idle routines kicked right in. That drops voltage to 0.00v as well as a solid 0% throttle position. Unfortunately, when you plug it back in, voltage goes back to .47 but throttle position goes up to 11-13% and the idle rpm really runs away. Guys, I can't be the only one that has had this problem. Any tricks that you guys might suggest. At this point, if I have to wire in a relay and a momentary micro switch on the pedal, the owner is willing to do whatever. Damn street driven race cars!

[LosLS2]

So nobody over here has ever had this problem???? I find that hard to believe. This is the second car that I have doing it. The first one being mine. Not sure if this has to do with the speedo being disconnected or not. Maybe it has to do with the car not knowing what gear it is in as both were formerly M6 and now have full manual autos?

This is really frustrating me and seems to be something that should be easy to correct. Perhaps it's a change that the programming gurus can make to the tune. I just want it fixed!!!

[Bluecat]

I've seen this problem dozens of times. Mostly on 98 cars. Some kind of ground plane issue. It has nothing to do with the tps voltage being to high, its just that it won't stay in the same place during different conditions and electrical loads.

Probally not relavent to you, but a few years ago I had a rash of people not getting both grounds on the back of the head hooked back up when doign engine work. When I'd get a call that the car wouldn't start after a engine install, the first thing I would have them try was grounding the pcm case and see if it would start. It would, but instead of actually hooking up the factory ground, they would just run a wire from the pcm to the body. (In these situations the HPT cable being hooked up will also make them start because it ties the two ground planes together at the obd port, funny story...)

Anyway, turns out that being lazy and doing it that way always creates the problem you speak of. But I've also seen it when the grounds are all correct. A few times running a extra ground from the pcm case to the engine block helped (not body).

When you can't physically get the tps volatge to be consistant, I've always been able to crutch it in the tune. Its not labled as the idle routine threshold, but aparently this value has more then one role. Rasing the "engine>spark advance>min tps" up to 3%, Always worked for me. Keeps the idle control active if its bounces up to 1 or 2%. I've also always changed the idle throttle follower airflow table so that it's zero up to 3%, but I don't know if you really have to.

[12secSS]

As Bluecat mentioned, it could be a ground plane issue. Now that you mentioned unplkugging it and it settles right in, it clicked a bulb in my head. I experienced this on a car. I checked the voltages on the TPS, and for shits and giggles I check the ground. Nothing! So I temporarily ran a ground to the TPS sensor and all was fine.

It's amazing what a little information can do to help troubleshoot an issue.

[LosLS2]

Good stuff. Now we are getting somewhere. We are going to "t" another wire on the ground, get it to where it is not running the idle routines and touch it to the body to see if the idle routines kick back in. Should know in the next 10 min if this works.

[LosLS2]

We cut the ground wire completely off the plug and grounded it to the chassis. Now we are getting 11-14% throttle position all the time.

Before that we tried T'ing in a ground and everytime that I would touch it to the chassis, the idle would go up 1 to 2 percent. Why is an additional ground making a higher TP %?

[LosLS2]

I'm going to send an email to Chris @ Hptuners and see if maybe someone with an intimate knowledge of what the software is actually doing here can help out. Makes no sense that a lower voltage would result in a higher throttle position value.

[LosLS2]

In theory, if we could get 5V power and a solid ground from another source and we just hooked up the signal wire to the PCM, should it work? We aren't there yet. We are adding another ground to the motor to see if that helps.

[Chris@HPTuners]

ok for apative idle airflow (ie. closed loop IAC control) to kick in there needs to be no throttle follower or throttle cracker airflow. You'll see that you have throttle follower airflow starting for TPS > 0.5% which is likely your problem since the TPS is not going to 0% reliably.

Make this table 0 up to 2% or something and this might be the fix.

Also as others have said, IAC going to zero is not desirable because the PCM will pull a lot of timing out to try to keep the idle RPM down, even down to -10deg etc. Usually you'll get a code becuase of this or your idle will repeatedly jump up again as the PCM resets itself to try and recover from the fault.