idle timing correction/TPS issues

[hymey]

Hey guys,

I got a phone call today from a workshop I do some work for from time to time. I never really know what they have in store as its always something different. Car in question VT SS, 346 forged internals, 238-244-110 cam. I built a base tune for it and got the maiden start on it once I got it to 80 deg C I started logging IAC counts there at 140 timing around 20-25 degrees, Idling initially at 1000rpm, It idled decent very choppy from lots of overlap. It has a FAST cable 92 mm TB fitted.

What was happening was at times the idle timing controls would cease working i would press the pedal a few times and they started working again, It was not going into the idle tables. The aftermarket TB hadn't been setup. The IAC counts are fairly high I need to adjust the screw and redo the airflow tables.

I figured as the TPS was reading 0% that it should be in idle mode. Due to it being intermittent I am thinking possibly the voltage was to high on the tps at idle and after i adjust the screw and get the iac steps around 50 I can reset the tps and check the voltage again.

Another thing I noticed was the startup was effected sometimes it fired straight up and others it didnt Im thinking it is due to the pcm not using the idle tables at startup after it did start it was idling on the high timing table, i would shut it down play with the pedal and get it to fire first kick and coincidently it would be using the idle timing map with timing correction making changes.

I am confident this is the problem, I really would like to be down there now tinkering but will have to wait till the morning. This is the first time I have encountered this with the FAST even without calibrating the TPS.

Has anyone had similiar experiences?

Cheers

Joel

[hymey]

I went down to the workshop this afternoon to work out the issue, The tps was flickering between 0 and 1%. It was set at .8v throttle closed. The IAC position was 140 at idle. I needed to open the blade more and set the tps correctly. I used a small round file and slotted the tps and adjusted the idle screw up. I got the blade up to achieve a nice idle with a 40 IAC count. I am not using any STIT corrections, not required.Although i need to iac count right so i could get enough additional airflow cold start. The tps is set back to 0.5V and i had 0% I then reset it in its new position also had to pull 20% fuel out of cranking ve the big cam didnt like it. Now with TPS in the 0.4-.6V range and TPS at 0 and IAC in a good spot.

Its idling happy and very suprisingly in CL at 900rpm and 20 deg lead, which is all it required with the 240s 110LSA cam. Got the low speed fuel and timing done, Now the easy bit of wot tuning tomorrow.

Hopefully this info will be useful to others..

[joecar]

Hi Joel,

Do you have any pics of the TPS modified...?

Thanks for posting...

[swingtan]

I've had the "no idle spark correction" thing a few times, but it was nearly always just after a re-flash. I think some PCM's may want a little extra time to reset completely before starting the car.

Simon.

[Steve Bryant]

Joel,
This is helpful. Thanks for posting!

Steve