Not long ago my 1997 Jimmy 4.3 Vortec started idling fast 1500-2000 rpm. After searching for the problem I finally found it. A small aluminum half moon shaped piece under the throttle intake air valve had caught on the EGR inlet in the intake and had bent downward not allowing my throttle valve to close fully. When I tried to bend it back into place it broke off, I looked it over and couldn't really find any actual use to the damn thing so I tossed it. Ever since then my idle is still around 1000-1500 rpm and my computor is tossing out P0300 (multiple cylinder misfire) after warm up. Does that half moon shaped piece really make that much difference in how the air/fuel mixes. Sometimes bank 1 cylinders are running lean, then the bank 2 cylinders will run rich. So far I've put in a new fuelpump since it was getting loud and fuel pressure was fluxuating. I put on a new catalytic converter and two new O2 sensors. and I also put in a new cam sensor. After all this it is still putting out the P0300 code. Any ideas.

 

haha the coveted throttle restriction plate...its held on by 2 pop rivets...if one of those falls out after youve taken it off and gets into one of hte cylinders you could have some major issues...i took mine off and put two new rivets in their place and had to drill a new idle hole for one reason or another...(been about 4-5 years so i cant remember why) but check to see if you lost a rivet.

 

Rivets are still in place. Should I go ahead and buy a replacement restriction plate?

 

Nah, I've taken it out of my 350 vortec and my friends 4.3 All it was there for was to "smooth out" throttle response for people that wanted their truck to drive like a cadi. Any lean and high idle problems are probably unrelated. However, when you put rivits in did you put the throttle plate back in correctly? When I did mine I put it in backwords at first and didn't even realise it, it won't close all the way when its in backwords.

 

I haven't replaced it yet, the old rivets are still in place. I have an O2 sensor taking a dump on me on Bank 1 Sensor 1. I'm gonna replace that one, hopefully things will smooth out.

 

If you feel bad about it, buy a replacement blade (without restrictor) here:
http://www.cfm-tech.com/
I have had a 98 and a 2002 S-10 and done this mod twice. The first time I yanked the restrictor plate off, without pulling the rivets out. If you look at the restrictor plate (depending on the year I think), sometimes it is over top of the idle hole in the throttle plate. The hole goes through both, but the hole in the blade is actually larger, so now you are getting more air. On my 2002 (if memory serves me correctly) they actually moved the idle air hole on the opposite side of the blade. Rather than mess with it (the car only had a few thousand miles on it, and was under warranty), I bought the cfm-tech replacement blade. It worked perfectly. The 4.3 is an excellent engine to work on, and is very responsive to modifications. Unfortunately the camshaft and intake manifold cause the most restriction...

 

I remember taking off the intake bonnet when doing my blower and seeing it hanging on for dear life so i took off the TB pulled it off, drilled out the rivets & put 2 new ones in...then drilling the idle hole bigger...takes the same time & with the same results...they respond real well to nitrous...ok to forced induction, your right though the intake/injection setup blows.

 

Well I managed to get the idle down to 850 rpms when in park and replaced the bank 1 sensor 1 O2 sensor. Now here is what is strange my intake is caked with black soot, and whenever I'm driving it if I put the tranny in neutral while I'm coasting my rpm's are at anywhere between 1300 to 1500 rpms. But as soon as I park the rpms drop back to normal. Any ideas? Is the computor misreading something, I'm not getting any codes now.

 

UHH. glad to see that someone had the same problem. I had the stuck throttle issue, looked at my throttle plate and that "half moon" piece that was there is now GONE!!!!!

-vehicle has been run, Its my daily driver. I'm VERY VERY concerned.

I'm thinking I'll have to remove the plenum. Will I find it there or will I have to go deeper? Will I have to remove the ENTIRE intake? If I remove the entire intake, will I find it there? I'm not familiar with the port sizes, location, bends and direction to know where this part could be.

I have not experienced any mechanical failure -yet-
vehicle has loss of power and is having cat replaced tomorrow.

I know that if it slips in too far, its potentially terminal to my motor.

-any advice anyone could give here would be HIGHLY appreciated. I am making plans to remove the plenum, but If I find a leaky fuel regulator, I might as well be prepared to replace that stuff while I'm in there.

1999 GMC Jimmy 4x4 -4.3L V6 with central sequential electronic fuel injection (CSEFI)

I found an upper and lower intake disassembly video online, I have a haynes manual. -I'm looking for encouragement/discouragement.


here is the video if anyone is interested:
http://www.youtube.com/watch?v=cpWjF...BAF99E22D1BC95

 

I removed mine completely and it dramatically improved throttle response. It's great. YES you need to dig for it, definitely. Do whatever it takes to find it. If it's blocking an intake port, that port will run super rich and have potentially killed your cat.

 

intakes come off really easy and vortec motors are notorious for vacuum leaks so make sure you replace the gaskets. you prob wont find that piece air inside the intake it rather turbulent, so chances are if its gone your motor ate it. if its still running fine then you got lucky and it flew past the intake valve and right out the exhaust valve without bending one.