Idle hangs

[Jim Blackwood]

Here's the tune and a datalog attached. Modified 2 bar P01 '02 Camaro base file running a Buick 300 V8 N/A. (the charger is currently off the engine) Speed Density tune. Runs very well at present with minor detail tuning needs, the next one on the list being the idle drop on closed throttle.

When coming to a stop or when letting off the throttle generally the idle will hang up for awhile before dropping to 800rpm. This can be seconds to minutes and I have taken to blipping the throttle to get it to drop, which seems always to work.

However sometimes it will drop of it's own accord which leads me to think that the problem is NOT an inadequate throttle return spring, especially since I fitted a stiffer spring and it made no difference, but I'm not sure I'm seeing that on the datalog.

Other than that, I've got a little hesitation off idle transitions still and my startup and warmup settings could be improved a bit.My AFR% is <1 over most of the map, <3 everywhere. (only logged after warmup, guess that means there's nothing for you to look at there...)

So what do you guys think?

Jim

[Lakegoat]

Your base running airflow looks low in the 111 degree and up cells. Try adding 2.00 to all those cells---I don't know what mods you have and cant't see your afr chart or wideband input. Also, your idle spark is from 1-3 degrees. maybe the the 1 degree part should be about 16 degrees depending on mods and increase the other areas above that---just a start. Look at a stock tune and that would be a good starting point. Your idle is set to 700, not 800.

[Jim Blackwood]

Thanks, I'll check those things out. Not much in the way of mods with this engine. Except for bolt-ons it is a bone stock 2bbl 9:1 compression iron head Buick 300 engine. Kind of a test mule while I'm building it's replacement. It does have free flowing equal length headers, a 4bbl intake, and an Enderlie style combo throttle body/air cleaner so I expect that raises the HP to maybe around 200 or so and seems to have raised the hp peak a little, maybe closer to 5k. But all in all a very mild engine. Running Delphi 26lb injectors and Silverado COP. Otherwise all Delphi Camaro sensors.

I suspect the reason for the low advance at idle is the controller's attempt to hit that 700rpm idle target, which it is not doing. But the throttle body has the butterflies fully closed with the IAC at zero so really what else is there to do but to raise the idle target to 800? Put a shutoff valve on the PCV maybe? That's about all I can think of. You probably can't see the WB trace because it comes in on the EGR position pin, I think maybe it's p55? Anyway at the same spot on the trace as above the AFR was 14:1. Not sure I follow this "Your base running airflow looks low in the 111 degree and up cells" Is this Engine/Idle/RPM/Base Setpoint/Base? If so, then we're on the same page I think. I have set the minimum numbers to 800 as that seems to be where the engine is happy idling. I'll test in a couple days. I agree it would come off idle more smoothly with a little advance. Stock is in the 8-12 range with vacuum advance disconnected so with it probably 20-25 degrees. It'd definitely be happier that way but my idle would probably be a fair bit over 1000rpm. Hmm... Yeah I think that might account for it. Maybe I can get the advance to pull off faster.

I'm on the road today so limited in what I can do. Had the car out yesterday for several hours and it did very well. Starting has gotten noticeably quicker and easier, maybe there's some program learning going on there IDK. Or maybe conditions were just favorable but it did fine.

The idle hang never improved. Usually if left to it's own devices, when coming to a stop it will idle down after about 5-10 seconds of running about 1200-1500rpm. Sometimes much more infrequently it will hang for up to a minute or maybe a bit more. I suspect it is also hanging when I let up on the gas pedal from cruise as the car does not slow down anywhere as quickly as I think it should. Often it simply maintains speed for some indeterminate time. This is the part I'm most anxious to improve. Looking back over the log the rpm does seem to track the spark advance. Looks like that could be the key here, along with getting the IAC to drop out.

Jim

[Jim Blackwood]

I think I found the main problem.
I noticed while on a drive that if I lightly rested my foot on the gas pedal the idle would come down. Weird right? Checking with the scanner and a VOM showed that sure enough, the TPS was acting a little strange in that at fully closed it showed a slight voltage of around 1 or better and when slightly opened that then dropped off to 0% or half a volt. This is the second GM original tps I've had on the car and I've not been impressed with them at all.

So I dug a known good Ford TPS out of the bin and installed that and connected it up. Now it works the way it is supposed to and just on testing start up, idle, and throttle blip it's way closer to normal. Maybe a test drive tomorrow if it doesn't rain.

I'm going to blame this on the linkage rather than saying the GM TPS is a poor design even though that's what I think. I like the fact that the Ford TPS is spring loaded and doesn't depend on the shaft driving it for internal alignment whereas the GM one is a light press fit or a tight sliding fit on the shaft. I think any wobble in the shaft throws the TPS off and this accounted for the error. I installed a larger shaft with a larger bushing and less play while I was at it but the way the Ford TPS is coupled that really wouldn't matter.

I still have an issue with the IAC opening during cruise or decel and I'm not convinced this is going to help there but I will know more after a drive. Anyway I figured it would be good to close this thread out with the actual solution in case anyone else runs across this problem. It is of course a custom TB with a remote linkage mounted TPS.

Jim

BTW, the Ford TPS is set at .75v closed and gives a reading on the scanner of 0% then at WOT is slightly above 85%.

[blindsquirrel]

I agree, GM should absolutely redesign their defective throttle position sensors so that they will work properly on homemade throttle bodies. Who cares if they work right when used as intended...

p.s. Have you ever owned a Fiero?

[Jim Blackwood]

Exactly. What do they think us hot rodders are supposed to do if their stuff doesn't work as god intended?
No Fiero. Heard they were kinda combustible.

Jim