Hello guys,

I have recently had the issue of the engine shivering at idle/low rpm but goes away when i hit the gas.
Check engine is on and gives iac code though i changed it recently.
Mechanice checked for leaks from the manifold gasket found none and suggests it is the spider.
All fuel system parts along with spark plugs and wires are new.

Any suggestions on what can be the problem i do not want to spend unnecessary $.

Thanks

 

Is the mechanic willing to stand behind his diagnosis if he replaces the part and it doesn't fix the problem, or is he just guessing?

If not, better to find someone who can diagnose YOUR vehicle. On the Internet most of what you are going to get is a bunch of suggestions on what part to replace that supposedly "fixed" another person's vehicle.

If you are committed to go through the diagnostic process and willing to carefully follow instructions and do the work yourself, we can help. Otherwise you are best off to spend the money to get a proper diagnosis done.

What camp are you in?

 

Well if i wasn't committed to find the solution i wouldn't be here my friend. In all cases several mechanics suggested the same thing the spider itself or the spider valve. However no one will stand by his work in case it does not work.

That is why i decided to go through this myself as i usually do on minor fixes.
I would appreciate the help i can get to get the car driving smooth again.
​​​​​​Thanks

 

Easiest thing I can suggest is to try to force the computer to "relearn" the new electronics like the IAC valve and spider, if you haven't done so yet. Not just clearing the codes with a scanner, but actually unplugging the battery for 15-20 minutes.

I've never tried it on a 4.3, but I was working on a friend's Trailblazer with the inline 6 a while back. I had pulled the throttle body off to clean and reinstall it, and afterwards the Trailblazer refused to idle with the AC on. I pulled a battery cable for a little while while working on something else, reinstalled about 20 minutes later, and started the vehicle, and the issue went away immediately and never came back. The computer had gotten "use to" sensor readings with the dirty throttle body and half-clogged air passages and just wouldn't run properly once they were cleaned. Once reset, the computer then relearns the data it's getting from the sensors and teaches it'self the proper running parameters again.

Not saying that it will for sure work, but it's something worth trying that doesn't cost you anything but a little time.

 

Well i did that i while ago when i changed the o2 sensors and gotta say it did work back then as the car idled rough with the new ones but after unplugging the batter for around 15 min it went smooth. Not sure about this case though as what i am facing is definitely a combustion issue but i don't know from what!

 

Just want to mention that you should clean the passage for the iac valve. A new one can get stuck on the same carbon buildup that failed the other one.

 

Sorry, I have been off the forum around the holiday. You will need a decent scan tool that will read Enhanced GM Powertrain PIDs. What are you using for a scan tool? I can recommend an appropriate inexpensive scan tool for Android or i-phone (about $35), but I need to know what year Blazer we are working on and what phone you have. You will need to have your own scanner. Is the SES light on? What is the code number. Does it return after clearing?

If the scanner and IAC code takes us nowhere you will need to do compression testing and fuel pressure testing.

Both static and dynamic compression per this link. https://support.alldata.com/article/...pression-tests
Fuel pressure per this link. https://blazerforum.com/forum/2nd-ge...eakdown-88305/
You can get loaner compression tester and fuel pressure tester through local auto parts store as needed.

Let me know when you have an appropriate scan tool and are ready to begin.

 

To echo what LesMeyer said, I'd do some simple diagnostics before throwing parts at it. Pull the battery cable for 20 min or so (again) as Blazen_Red_4x4 mentioned and if that doesn't clear the code and fix it, think about doing a fuel pressure check to confirm or deny your mechanic's suspicions and go from there.

 

I cleaned the iac valve but the code is not from that. The code i keep getting is from the intake manifold temperature sensor which i changed new! I suspect that when i did the egr delete the technician cut a wire to forbid the code from popping back on the dashboard.

 

Well the code goes away for a while just until you take a long ride and the car heats up pretty well the code pops up again.
I changed o2 sensore filters spark plugs and wires all new.
And in addtion the car puts out black smoke when hitting gas and it only shivers while slowing or when idling at heat. It seems when going fast then trying to stop the car shivers for a while to adapt the speed
So i suspect the following:
Egr delete which i did long ago
Spider
Spider valve
Distributor cap

Please not that i checked for manifold air leaks and found none

Thanks