Idle Surge And Stalling IAC jumping around.

[Chuck Leeper]

The TPS is on the pass side of the throttle body.

 

[Dylan4570]

Just to keep things consistent.

This issue somewhat reared its head again this spring. My solution was to add a burden resistor within the ECM. no issues since.

I modified my ECM because of an intermittent AC request input signal

 

[priobe]

I know this is an old thread but direct message is not working.

Hello
I came across this post using Tuner Pro RT to diag the turbo Buick.
I just purchased my GN (had one 25 yrs ago) and noticed the idle is bad and running extremely rich. I suspect it’s the MAF and since it is a stock MAF I figured it would be good to purchase a translator with LT1.

My question is it seems as if you can use Tuner PRo to diag something things. I have to make a usb to ALDL connector and install the software.

I wanted to get some feedback before taking on this project to see if it is worth it.

Thanks

 

[Dylan4570]

I know this is an old thread but direct message is not working.

Hello
I came across this post using Tuner Pro RT to diag the turbo Buick.
I just purchased my GN (had one 25 yrs ago) and noticed the idle is bad and running extremely rich. I suspect it’s the MAF and since it is a stock MAF I figured it would be good to purchase a translator with LT1.

My question is it seems as if you can use Tuner PRo to diag something things. I have to make a usb to ALDL connector and install the software.

I wanted to get some feedback before taking on this project to see if it is worth it.

Thanks

Hi,

It's worth it. One concern I had was the implications of an aftermarket chip. With the Turbotweak chip, I was able to monitor the data stream without issue.

I think we used a standard XDF file?

"The datastream is the same as stock, so you should be able to use any scantool that works with the stock chip." - email from Eric @ turbotweak.

I think we used an FTDI232 with a pull-down resistor and a diode?

If you have any trouble, reply to the thread or message me, and we can actually document the setup. Maybe someone will jump in and post a link to a well-documented ALDL cable creation document and explain the process better.

EDIT: gearhead EFI has all the bin and XDF files and good info if i recall.

 

[CaptainTurbo]

As the vehicle warms up the idle surge will get worse and worse, eventually the car will stall. I have adjusted the min air screw to range all the way from 15 to 40 and regardless on setting the idle will not stabilize. TPS is 0.42 or 0.44 volts.

IAC will decrease to ~20 and then suddenly surge to ~70-90 and then the process will repeat, eventually worsening until the car stalls. I can see the vacuum drop and AFR lean out from 14 to 17 as it surges. With a 3 inch LT1 MAF and translator what should my MAF reading be at idle? could the MAF be failing? fuel pressure is ~43 line off ~35 line on.
I have tried a new ECM and it had no affect. Also did a IAC reset and that did not seem to affect it. It finally decided to stall while i was driving it.

I could parts cannon an IAC valve at it but am looking for something a little more certain. sometimes the car will throw a code - 41 when the idle gets really low and surges.

Pull your crankshaft sensor and see if it has started to rub. They have been known to produce some crazy symptoms.

 

[Dylan4570]

Pull your crankshaft sensor and see if it has started to rub. They have been known to produce some crazy symptoms.

issue was solved in post #22 with a link to the fix.