I have a Chev Corvair Dual TBI-700 setup and the car runs great, but I have a problem. The problem is complicated, the car idles 1600 rpms in Neu when the temp is below 160. The car will continue to idle at 1600 Neu/1000 in Drive (pulling hard) even when the car is at normal running temp unless I turn the car off and restart or re-upload (Romulator) the same bin file, if I do that the car will idle down to about 750 like is it suppose to and runs at the right idle. I already replaced the dual iac valves and the tps sensor, I have also changed the computer, and adjusted the bin file over 100 times and I am stuck!!!!. Its been a year and I'm having no luck a read and reread tuning papers about the same amount of times. I did take into account the dual IAC and 1/2'd the settings, but the same result. If I can't fix this, I'm going to another ECM (427), but it would be shame as this ECM is great except for the idle.

Sorry for the long post and highly adjusted bin attached for your review.

Ted Brown
68 Chev Corvair

 

Consider removing IAC control at idle? Set steps to zero for all temps above 150F. Then set idle with throttle stop screw.

Consider idleing OL? Now idle OL may not be available in 7747(i forget) but an experiment may be to disallow CL completely by setting the CL coolant to a high number on coolant temp. Just an experiment to see what happens. I ran OL 100% for a season. car ran fine(better) but gas mileage sufferred. I now run CL but OL idle and OL <20 mph.

 

If the system voltage jitters that can cause the ECM to hold the idle high. Zero the value at $5DC and set the value at $5DD to 255. That will eliminate idle correction based on the system voltage dropping.

Note that the kick down steps at $5D8 should be one higher then the lowest steps in the position table. IIRC having it the same does work, but GM always set it to one higher. In your case this would be 7 steps.

RBob.

 

corvair_nut did you ever get this fixed?

 

I think it helped a little, but No. I have about given up on the 7747 for the Corvair and going for the 16196395/427 as I have read it does a good job on idle. I love the 7747 as it performs well and does about everything I need except from cold to normal idle. It acts a little different each time, but usually ends up revving real high after almost konking out or the IAC counts stay at 35 until I restart (reboot) the ECM.

I little frustrated as I have a lot of time and money in this project to have to dump it and go to something else. I have a romulator that Im going to unload as I have the Rom-I and only supports upto 256 chip. Ordered the Rom-II today.

Thanks
ted

 

Update: I think I have found it, but it was a combination. I set the voltage jitter to 0 per RBob, but that did'nt do it so I pretty much had given up.

My VSS has stopped working and I decided to get it working (using a crank sensor with a switching transistor going high) since my speedo cable broke. After getting the pulses going to the ECM (even though not correct) as soon as the VSS started sending signal, the IAC counts started changing.

I used the timing table to stop the high rev idle that I get sometimes, but that hasnt been a problem lately neither.

This 1227747 is behaving nicely now and now Im going to continue with it a little while longer.

Thanks guys.

Ted
Anderson, SC
68 Corvair