it surged a lot. Okay it is normal for a 240duration cam, but I mean I must keep the gas pedal at ~2000rpm all the time while driving. I think something is wrong, because when I am driving down the road and put my car in neutral,the RPM drops, and suddenly engine stops. I MUST push the gas pedal and keep the RPM around 1500-2000rpm.
However while the car stops at idle, its just fine (~950rpm), while I'm driving, it stops if I don't push the gas pedal all the time.

Does anybody have any ideas of why this is the case? Bad idle speed sensor?

Any suggestion will be great!!

 

check your vacuum lines?

 

You need some real data from a datalogger to really help diagnose anything beyond guessing.

What throttlebody are you using?

 

Yes checked!

 

We connected GM Tech2 Scanner and no codes displayed.

BTW we tried to change (raise) the idle by using the scanner, but nothing changed. i.e. Car idles at 900rpm, we raised it to 1200rpm by Tech2, but it still idles around 900rpm.

58mm BBK with Granatelli MAF

 

How does the IAC reading look? Its probably maxed out... 160. I dont know what the limitation of a Tech2 is but Datamaster is EASY to read and use. Plus you can save files for other people to see.

 

Yes its 160.

My car is 97 and I got conversion OBD2 to OBD1 from Ion. I will definitaly get Scanmaster after I solved this problem.

 

See, the problem you are having and youre not the first or the last is that the IAC cant compensate enough to keep the motor alive. 160 is the max the IAC can open so you need to crack the TB blades a little to bring the number down around 50.

 

So thats the my problem?

I couldn't understand why car doesn't die while not running (not driving), but dies while running??? (Shift is neutral position in the same situation).

 

Just isnt getting enough air.

 

Okay I see that, but how can you explain my question. There is no any problem while car idles without running, but dies while driving. (in neutral shift)

 

It needs more air while moving because its under a bigger load, especially when you shut the throttle and a little extra fuel is in there, you need more air to keep from going dead rich and killing the motor

 

Oh okay thats a good explanation thanks. I can't drive around 10mph or less without pushing the clutch pedal, so this explains the reason right?
How can I fix this?

 

Gotta answer for this already


You can also drill a very tiny hole in the throttle blades, say 3/32nds and check the IAC counts then. If you change the idle set screw to open the throttle blades more at idle then your TPS voltage could get too high and throw a code that way. It's better to give the motor the extra air it needs with a small hole in the throttle blades and then let the IAC do it's job when you change throttle positions fast, like backing off the throttle while you are coming to a stop.

Start at 3/32nds with the hole and slowly go up till your IAC counts drop to 50, then the car should drive fine.

Do a search on IAC and you should find someone else recently who had this same issue and this is how it was resovled.

Bret

 

I drilled my IAC bypass hole bigger on my home ported 52 mm TB.

On aftermarket TBs you will have to drill the butterflies. Start with the smallest bit and go bigger until your IAC steps drop down into the 40s or until your drivability improves.